What does nitrogen smell like?


The 8 Home Smells That Could Be Signs of Danger

You think you smell fish—even though you haven’t cooked anything resembling salmon or swordfish in days. Or maybe it’s the smell of your fireplace—even though you haven’t set fire to a log in weeks. Or the odor resembles ammonia, rotten eggs or something else entirely.

Such household odors can serve as clues that there are hidden dangers in the home—problems that could be pricier to repair and potentially hazardous to your health if not found and fixed fast.

Here’s what home owners need to know about eight home odors…

Fishy smell that’s not fish. Some people refer to this as a urine or burning rubber smell. This could be something electrical in the home overheating and melting its insulating plastic or ­rubber—which could lead to a fire.

The most likely culprit is an appliance, such as a dishwasher, washing machine or an air conditioner. Sniff near each of these while they are running to try to identify the source. When you think you have found the source, either call in a repair professional to investigate…or replace the appliance if it is approaching the end of its useful life.

Warning: If the odor seems to be emanating from a wall switch, outlet or some other part of your home’s electrical wiring, not an appliance, switch off the circuit breaker and call an ­electrician.

Ammonia smell that’s not ammonia. Some people describe this as the smell of death, and they’re right—a mouse or some other small animal likely has died inside your home. One solution is to find and remove the corpse, and that’s often easier said than done—there’s a good chance that it is in a hard-to-reach spot inside your walls, ceiling or floor.

Use your nose to find where the smell is strongest, and search everywhere you can in that area. Consider buying and using a small snaking digital inspection camera to peek into walls, behind cabinets and appliances and into other tight spots. Ridgid Hand-Held inspection cameras are a good choice, starting at less than $150.

Unfortunately, even with a snaking camera, you won’t be able to see everywhere without drilling holes in walls, and that usually causes more problems than it solves. Of course, you could just wait for the smell to go away, which typically takes a few weeks.

Meanwhile, inspect the perimeter of your home for gaps where rodents can enter, and seal these to prevent further invasions. Also, deploy rodent traps—not rodent poison—in the home. If you use poison, additional rodents might die in their hard-to-reach nests inside your home, creating more bad smell.

Damp, musty smell. This usually signals mold or mildew, which could become a big problem for both your home and your health if not quickly remedied. Use a digital ­hygrometer to check the relative humidity of each room in the house—you can find these for less than $10 online or at home-improvement stores. If you get readings above 50%, run a dehumidifier. Apply an antimicrobial spray to carpets, curtains and fabric-covered furniture in any room that has high humidity and/or a musty odor.

Meanwhile, search these rooms for water leaks. Look behind refrigerators and under sinks for wet spots. Visit the room during the next hard rain to look for visible leaks. Go down to the basement, crawl space or room directly beneath this musty room to look for evidence of water leaks there, too—those could point to leaks that are hard to spot in the room above.

Musty/smoky odor from a fireplace that’s not in use. First, make sure that the chimney dampers are closed. Chimney smells can be drawn into the house when these are left open.

If that’s not the problem, vacuum and then scrub the “firebox”—the area that contains the fire at the base of the chimney. If the smell persists after the firebox has dried following this cleaning, call in a chimney sweep to clean and inspect your chimney. Mention that you suspect water might be getting in. The problem might be as simple as a dislodged chimney cap, or there might be cracks in the masonry.

Make sure the chimney sweep checks whether the damper is sealing ­sufficiently. You can purchase and use an inflatable damper, sometimes called a fireplace draft stopper. These are available for less than $100.

Dusty burning smell when you turn on your heat for the first time in months. Burning smells understandably trigger home owner anxieties, but this one usually is not a problem—the dust that settled on the unit over the summer is simply burning away. This smell should disappear on its own within a few hours of turning on the heat. Do replace your HVAC system’s filter if you haven’t done so recently because it might be allowing excessive dust to collect on heating components.

Warning: Turn off your heating system, and call in an HVAC repair pro if you see smoke coming from vents and/or the burning smell occurs at any time other than the heating system’s first few uses of the season.

Chemical smell from new furniture, carpet or paint. A fresh coat of paint, a new piece of pressed-board furniture or a new carpet can off-gas volatile organic compounds (VOCs) that are not just unpleasant to smell but also unhealthy to breathe. When possible, remove new pressed-wood furniture and carpeting from its packaging and let it air out in your garage for at least an hour, and preferably overnight, before bringing it into your home. If that isn’t feasible, open all the windows in the room and run fans to circulate the air for at least an hour and as long as a full day. That method also works when you are painting interior walls.

Sewage smell. This sometimes is confused with the rotten-egg smell described in the box on page four, but it’s less “eggy” and more like the smell of an outhouse or a portable toilet. It probably is coming from a drain. Use your nose to determine which one—it could be the drain of a toilet, sink, tub or shower.

One possibility is that there isn’t enough water in this drain’s “P trap.” The P trap is a curved piece of pipe below the drain that should be full of water—the water blocks offensive odors from your sewer line or septic tank from wafting back into the house. If this is the case, running the water for a few seconds (or flushing the toilet) should solve the problem. You also will have to air out the house to get rid of the odor that’s already there. This is especially likely if the toilet, sink, tub or shower has gone unused for months—the water in the P trap might have evaporated.

If that does not solve the problem—or if you see that the water is not draining properly—the odor probably is coming from material clogged in the drain line. Put on rubber gloves, and use a flexible 16-to-18-inch drain-cleaning brush to clear out any gunk from the drain. Next, let the hot water run for a few minutes (or flush the toilet) to confirm that it is now draining properly. Then shut off the water and pour one cup of bleach into the drain. Let the bleach sit for 30 to 60 minutes, then run the hot water (or flush the toilet) again. If the odor persists, you may need to rent or purchase a plumber’s auger or snake to dislodge the clog.

Rotten-Egg Smell Could Be Two Things

A rotten-egg smell might be a potentially dangerous natural gas leak. Get everyone out of the house—leaving the door and windows open so that some gas can escape—and call your gas company immediately to report the problem and request further instructions. Natural gas itself is odorless, but a sulfurlike rotten-egg smell is added so that leaks will be detected.

If a faint rotten-egg smell occurs only when your hot water is running, however, it’s probably not a gas leak at all but rather a small amount of odorous sulfur in the water. Sometimes you or a plumber can solve this problem by shutting off the water line leading to the water heater, using a hose to drain the tank, then refilling the tank.

Avoid a compost that smells of sulphur, ammonia and rotten meat

Five rules to avoid a stinky compost heap

Healthy compost heaps shouldn’t smell bad, and they most certainly shouldn’t provoke a full hazmat reaction as happened at two Wairarapa schools on Friday.

There, more than 100 students and teachers were put through a decontamination process , and 10 children were taken to hospital with dizziness, nausea and headaches.

PIERS FULLER/STUFF Carterton homeowner Illya McLellan and his load of compost which sparked the emergency response at a school next door.

While all have since been discharged with no lasting effects, the incident has been blamed on fresh mushroom compost in a heap on a nearby property, which the children reported as smelling like rotting pig flesh and rotten eggs.

Now that the sulphurous fumes have cleared, it seems timely to revisit some basic composting principles to help you make use of organic waste in your garden without triggering an emergency decontamination response team.

SUPPLIED Good compost should smell rich and earthy.

* Twenty-four weird things you can compost
* How to start a compost heap
* Kids’ guide to what to compost

First off, let’s define our terms. Compost is the end product you want to have left after a mix of organic material breaks down. And organic material breaks down because of biological activity – specifically soil bacterial and fungi that eat and then excrete that organic matter, turning it into beautiful crumbly soil-enriching compost.

That compost, if it’s well made, should smell earthy but not unpleasant. But sometimes organic waste can give off a foul stench as it breaks down and there are a variety of reasons for that.

RACHEL OLDHAM/STUFF A compost heap should contain a mix of suitable carbon-rich (brown) and nitrogen-rich (green) material.

If your compost smells like sulphur or rotten eggs
This happens when your compost heap is decomposing anaerobically, which literally means without oxygen.

All those millions of good soil-dwelling bacteria and fungi that you want there, breaking down your vege peels and green waste into a useful soil enrichment, need oxygen to function. If your compost heap doesn’t provide the oxygen they need, you’ll find anaerobic soil microorganisms there instead. They can work in the no-oxygen environment … but as they do so they produce hydrogen sulfide as a by-product (fun fact: hydrogen sulphur emissions are also what gives Rotorua its distinctively pungent bouquet).

If you notice any such pong around your compost heap, check to see it is not too wet or too tightly packed. Water will fill the spaces between the soil particles, so there’s no room for air there, while compaction means there’s no spaces in between the particles for air in the first place.

Eva Bradley Bokashi composting bins used to ferment organic waste.garden.

Compost heaps will also start decomposing anaerobically when they contain too much “green” or nitrogen-rich material – that’s vege scraps, grass clippings and plant waste; and not enough “brown” or carbon-rich organic matter – such as dried leaves, torn up newspaper or cardboard, or straw.

Luckily whether your heap is wet, compacted or your carbon to nitrogen ratio is off, the solution is the same. Add some “brown” material and turn your heap using a pitch fork to get some air in for those helpful soil microorganisms.

If your compost smells like ammonia
Again this happens when your compost heap contains too much “green” or nitrogen-rich material, and so starts giving off the excess nitrogen (N) in the form of ammonia (NH3).

And so the solution is once again to add more carbon-containing organic matter and turn it into your heap to mix it in thoroughly.

MARTIN DE RUYTER Meat, dairy and fats give off putrid odours as they break down so keep them out of your home compost.

If your compost smells like rotten meat
The obvious reason your compost will start to reek of decaying meat is you’ve added, well, meat to it and it’s starting to decay.

Meats, fat and dairy all give off putrid odours as they break down, as well as attracting the likes of rats and blowflies, so it’s not a good idea to add any of them to your home compost (although if you do want to compost meat or dairy, try using a bokashi system).

Three simple rules to avoid stinky compost
– A properly made compost heap shouldn’t smell bad and if it does you need to add carbon-rich material or turn the heap, probably both. You should aim to turn compost every week or so, maybe more often in hot weather.

– By properly made, I mean a compost heap should contain a mix of suitable carbon-rich (brown) and nitrogen-rich (green) material. Aim for about three parts brown to one part green.

– And remember, small pieces are better. Chopping or shredding leaves, plant matter and vege scraps will increase their surface air, and therefore the amount of air available to the composting microorganisms.


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Ammonia Smell

by Robert Spies
(Tempe Az)

i just started composting using a aerobin 400

added a layer of dried leaves, then a layer of active compost from home depot.
have been adding chopped up veggies and fruits, an activator, shredded paper.
it has only been a week and it smell like ammonia
live in az, weather about 90 degrees
also added a little water
is this a normal smell? does not smell like rotting garbage
r j spies md

Handling the Ammonia Smell
Hi Robert.
The ammonia smell often occurs in composting. Ammonia is a type of fixed nitrogen and is used to make various nitrogen fertilizers.
I checked out the aerobin 400 just in case it was part of the problem. I don’t think it is. It looks like a bin that would work well and maintain adequate airflow.
If you have a lot of nitrogen in your compost there is a chance that the excess will off gas as ammonia. The high nitrogen items in your compost are the chopped up veggies and fruits and the activator.
I would omit the activator now. Activators are useful when you don’t have enough nitrogen rich materials for your compost. You have enough nitrogen without the activator so just stop using it. Things should settle quickly.
If the problem continues add more high carbon materials – like your shredded paper. Mix it up as well as possible with the greens you are adding.
Finally, in Arizona, as you know it is very dry. I live in a very dry area too. The one thing to keep an eye on is the moisture in the compost. If it gets too dry the whole composting process stops. Instead of compost you’ll get mummified garbage. The bin you are using may help but if things do get dry do add water and mix it up.
Good luck with this.
Leslie – The Compost Gardener

Treating Common Ammonia Odors In The Garden

Ammonia smell in gardens is a common problem for the home composter. The odor is the result of inefficient breakdown of organic compounds. Ammonia detection in soil is as simple as using your nose, but the cause is a scientific matter. Treatments are easy with a few trick and tips found here.

Composting is a time honored garden tradition and results in rich soil and nutrient density for plants. Ammonia smell in gardens and compost heaps is an indicator of inadequate oxygen for microbial activity. Organic compounds cannot compost without adequate oxygen, but the fix is a simple one by introducing more oxygen to the soil.

Compost Ammonia Odor

Compost ammonia odor is frequently observed in piles of organic matter which have not been turned. Turning of compost introduces more oxygen to the matter, which in turn enhances the work of the microbes and bacteria that break down the matter. Additionally, compost that is too rich in nitrogen requires air circulation and the introduction of a balancing carbon, such as dry leaves.

Mulch piles that are too moist and do not get air exposure are also prone to such odors. When mulch smells like ammonia, simply turn it frequently and mix in straw, leaf litter or even shredded newspaper. Avoid adding more nitrogen-rich plant matter such as grass clippings until the smell is gone and the pile is balanced.

Compost ammonia odor should dissipate over time with the addition of carbon and frequently moving the pile to add oxygen.

Garden Bed Odors

Purchased mulch and compost may not have been processed fully, leading to anaerobic odors such as ammonia or sulfur. You can use a soil test for ammonia detection in soil, but extreme conditions will be obvious just from the smell. The soil test can indicate if pH is too low, around 2.2 to 3.5, which is harmful to most plants.

This mulch is called sour mulch, and if you spread it around your plants, they will quickly become adversely affected and may die. Rake or dig out any areas where sour mulch has been applied and pile up the bad soil. Add carbon to the mixture weekly and turn the pile frequently to correct the problem.

Treating Common Ammonia Odors

Industrial treatment plants use chemicals to balance bio-solids and composting organic materials. They can introduce oxygen through a forced aeration system. Chemicals such as hydrogen peroxide and chlorine are part of professional systems but the average homeowner shouldn’t resort to such measures. Treating common ammonia odors in the home landscape may be done by the addition of carbon or simply applying liberal amounts of water to leach the soil and a lime treatment to increase the soil pH.

Tilling in leaf litter, straw, hay, wood chips and even shredded cardboard will gradually fix the problem when mulch smells like ammonia. Sterilizing the soil also works, by killing off the bacteria, which are releasing the odor as they consume the excess nitrogen in the soil. This is simple to do by covering the affected area with black plastic mulch in the summer. The concentrated solar heat, cooks the soil, killing the bacteria. You will still need to balance the soil with carbon and turn it after the soil cooks for a week or more.

DEAR JOAN: I share with you and your readers the appearance of a beautiful but locally rare fungus in the Bay Area.

It was originally described in the scientific literature in 1729. Creative comparisons of its appearance are “like a wiffleball,” and, from a German mycologist, as “like an alien from a science fiction horror film.”

I am a biologist and just had to identify this fungus.

Last fall an orange unknown thing appeared among the leaves in our garden. I thought it was a discarded piece of packing foam but on closer inspection I realized it was a delicate and intricate cage-like fungus — a hollow ball with interlaced branches.

I researched and identified the fungus as Clathrus ruber, Red Cage Stinkhorn fungus. It dramatically erupts from a whitish “egg” with a delicate leathery outer membrane to form a large red cage filled with a brown slime containing spores. It relies on flies for distribution.

The slime has a rotten meat smell that attracts flies, which get coated in the spore containing slime and carry it away to germinate into a new crop of fungi. The fungus is saprobic, feeding off decaying woody plant material.

This year, another Clathrus rubergrouping appeared nestled among wood chip garden mulch. This fungus is relatively rare but a beautiful sight to behold. Its foul smell would dissuade most people from eating it.

Elaine Anderson, Stanford

DEAR ELAINE: What an amazing find, and thanks for letting us know about it. If I found that in my yard, I probably would have jumped to a lot of wrong conclusions.

DEAR JOAN: I just installed a drip irrigation system with plastic pipes. It seems the squirrels like my pipes more than they like acorns. They chew through them to get water. What can I do?

Jim Colton, Palo Alto

DEAR JIM: Congrats on the new irrigation system and squirrel watering station.

Convincing squirrels to leave your things alone can be a full-time job. The easiest solution is in the category of “if you can’t beat them, join them.” Although squirrels have an actual need to chew on things — their teeth continue to grow so they must gnaw to keep them under control — in the case of irrigation lines, they’re probably just looking for water.

Try giving them their own source of water, or place a dish beneath an emitter so they can get water without having to destroy your lines.

You also can try wrapping the larger pipes and flexible tubing in landscape cloth or wire mesh. That involves a lot of work and it won’t be attractive, but it might solve your problem.

As we’re nearing our cold season, you should drain your lines, which will make them less attractive to the squirrels until you hook them up again in the spring.

If the squirrels are attacking one section of the irrigation system, try coating the pipes in hot pepper sauce, sprinkling dried chilies around them or setting out small bowls of hot sauce near the lines.

Readers, do you have experience with squirrels and irrigation lines? If so, I’d love to hear your success stories and failures, which I’m guessing probably outweigh the wins.

UConn Home & Garden Education Center

Mulch Basics

Printable PDF
What Is Mulch?
A mulch is any material, organic or inorganic, that is placed on top of the soil in a garden or landscape. Mulches are one of a gardener’s most valuable tools and an essential component of low-maintenance landscapes.
Benefits of Mulches
Aside from their decorative value, mulches offer many benefits to your soil and plants. Mulch reduces the amount of water lost through evaporation by shielding the soil from the sun’s drying rays. It keeps the soil cooler during the summer and acts as an insulator through the cold winter months lessening the effects of fluctuating temperatures on plant roots which in turn decreases their susceptibility to frost heaving. Organic matter is added to the soil as the mulch breaks down. Increasing the soil organic matter will improve a soil’s moisture and nutrient holding capacity, structure, and drainage. Mulch also encourages the activity of beneficial soil organisms. Weed growth is suppressed by the use of a mulch as is the spread of some plant diseases. Mulched plots are also less prone to erosion.
Organic Versus Inorganic
Organic mulches are derived from natural materials that decompose over time. As organic mulches decompose, they add nutrients and organic matter to the soil and beneficial microorganisms like nitrifying bacteria and mycorrhizal fungi are enhanced while undesirable pathogens – those that cause plant diseases are inhibited. Increased amounts of organic matter will improve soil tilth and drainage, increase soil moisture retention, reduce soil compaction, and attract earthworms. Because organic mulches decompose, they need to be replaced. Depending on the type of mulch used, replacement intervals vary from one to four years.
Inorganic mulches include stones, geotextile mats and landscape fabrics, and plastic mulches. Landscape fabrics and plastic mulches deteriorate with time and eventually require replacement. Inorganic mulches usually are more tedious to install and may require irrigation because water penetration may be limited. Some inorganic mulches are designed to reflect the sky to confuse and keep insects from landing on plants. Many do not have a natural appearance and are often covered by an organic mulch for decorative purposes.
General Tips for Applying Mulches

  • Do not place mulch directly against plant crowns or tree bases. Mulch placed directly in contact with stems or tree trunks may retain excess moisture around the base of the plant that can favor the development of diseases like crown rot. Mulch piled around plants may also serve as lodging for bark and stem eating rodents. Avoid ‘volcano’ mulching where mulch is piled into a large cone shape against tree trunks.Pull mulch away from the base of the trunk.

  • Mulch applied too thickly can cause problems. A wood-derived mulch may undergo high temperature decomposition causing it to dry out. The mulch may then be colonized by fungi that create water repellent conditions throughout the mulch. Water is unable to penetrate the mulch and reach the soil and plants fail to receive adequate moisture. Mulching too deeply can also cause the soil to remain continuously wet contributing to root and stem rot problems in addition to depriving plants of needed oxygen. Apply a mulch layer no more than 1 to 3 inches thick.

  • Thoroughly water newly installed wood or bark mulches. Many good quality mulches are stored in large piles that reach high temperatures. When the mulch is spread or bagged, the high-temperature tolerant microorganisms that inhabit the mulch die as the mulch cools. If the mulch is allowed to dry out or remain dry, nuisance fungi can colonize the mulch and create a water-repellent surface.

  • Add a source of nitrogen to garden soils before applying wood-derived mulches. Soil microorganisms that decompose organic materials such as wood-based mulches are effective competitors for limited soil nitrogen. This may cause temporary nitrogen deficiencies especially in annual and perennial plants. Yellowing of leaves often indicates a nitrogen deficiency. Lightly incorporate a source of nitrogen such as bloodmeal, urea or a high nitrogen lawn fertilizer before applying mulch.

Types of Organic Mulches




Shredded Bark

Keeps soil cool and moist. Readily available. Good weed control. Appropriate for ornamentals.

During especially wet years, sour mulch may be a problem.

Hardwood bark will need to be replaced more frequently than softwood bark.

Wood Chips

Decorative, controls weeds.

High carbon wood chips may cause a temporary nitrogen deficiency. Most appropriate for paths or under large shrubs or trees.Susceptible to Artillery fungus.

Wood waste products may be added to this type of mulch product. Sometimes they are colored. Check with your source.


Inexpensive. Slow to decompose.

Ties up nitrogen in the soil. Slow water penetration.

Let weather a few months before using.

Buckwheat Hulls

Good for small plants, flowers, and vegetable gardens. Very attractive.

Will blow away if placed in windy, exposed areas. Expensive.

Stays in place if kept wet and as it ages.

Cocoa Shells

Good for small plants, flowers, and vegetable gardens. Smells like chocolate.

Toxic to dogs. Will blow away if placed in windy, exposed areas. Expensive. May mold.

Wash away any mold that appears. Stays in place if kept wet and as it ages.


Great winter insulator for bulbs, vegetables and perennials. Useful in garden paths and around larger vegetables.

May contain weed seeds. Sometimes blows around when dry. Flammable.

Apply a 4 to 6-inch layer. Hay from late season cuttings is often harvested before it goes to seed.

Salt Marsh Hay

Good winter insulator for bulbs, vegetables, and perennials. Useful as a summer mulch.

Will blow around when dry. Flammable. Not always available.

Weed-free as seeds require salt water for germination. Sold locally at some garden centers.

Grass Clippings

Great use for unwanted lawn clippings. Free and contains nutrients.

Decomposes quickly. Mixing with peat moss will slow decomposition rate. Weed seeds.

Do not use clippings from herbicide and/or insecticide treated lawns. Apply a 3 to 4-inch layer. Fluff up if clippings begin to smell.

Pine Needles

Good for acid-loving plants. Winter mulch for strawberries.

Only available to those that have access to pine trees.

Slow decomposition rate so add organic matter to the soil before mulching if level is low.


Good winter insulator. Contains a fair amount of plant nutrients.

Will blow around when dry. Maple and poplar leaves tend to pack together.

Chopped leaves do not blow around as easily and look attractive. Apply a 2 to 4-inch layer.


Excellent weed suppresser. No longer contains lead in the newsprint.

Does contain carcinogens in small amounts. Flammable when dry.

Put in vegetable garden paths and top with hay or wood chips. Use at least 2 layers.


Source of nutrients. Good for disease control.
Improves soil and attracts earthworms.

Immature compost may cause a nutrient imbalance and/or contain high soluble salts.

Compost is ready when raw materials are decomposed and not readily recognizable.

Types of Inorganic Mulches





Low maintenance mulch. Decorative. Great for pathways.

Weeds can germinate between stones. Stones will filter into the soil over time. Difficult to incorporate amendments into soil under stones.

A layer of black plastic mulch or landscape fabric may keep stones from sinking into the soil. Keep stones from touching plants. Site may be too hot for some plants.


Most useful in the vegetable garden. Warms soil. Excellent weed control.

Need irrigation system or holes punched in the plastic to allow water to reach plants and soil.

Black plastic mulch is used to warm the soil for heat-loving vegetables. White or silver plastic mulch is said to confused insects. Red colored mulch may increase tomato yields.

Landscape Fabrics

Excellent weed control in vegetable garden. Useful for soil stabilization. Specially designed mats
for use around trees.

Does nothing to improve the soil. Weeds may grow through upper layer. Will degrade with time.

Layer sheets over one another to prevent weeds from germinating between sheets. Can be covered with a more attractive organic mulch.

Common Mulch Problems
Artillery Fungus
Artillery fungus (Sphaerobolus spp.) colonize organic matter such as wood mulch (as opposed to bark mulch). The tiny, cream or orange-brown fruiting structures are shaped like cups that contain a small black spore mass. The fungus “shoots” the spore mass into the air and it sticks to any surface it hits. The small black spots will be visible on plant leaves and/or home siding, and they are very difficult to remove. Pine or Atlantic white cedar bark nuggets are the most artillery fungus resistant. Cypress also exhibits some anti-fungal properties but it is a non-sustainable product. If wood chips/mulch are used a fresh inch applied each year may help to contain the fungal spores.
Incorporating mushroom compost at a rate of 20-40% into existing or new landscape mulch beds may suppress artillery fungus. Mushroom compost is available commercially.
Slime Molds
Slime molds are bright yellow or orange slimy masses reaching a foot or more in diameter. They produce tiny spores, which eventually will dry and blow away. These molds are not a serious problem and can be considered a decorative addition to the landscape. Remove them if you find their appearance undesirable.
Sour Mulch
If a mulch smells like alcohol, vinegar, ammonia, or sulfur it is probably “sour.” The smell is created when a wood-derived mulch is piled high and the inside portion of the pile is deprived of oxygen. This causes anaerobic activity, which creates a build-up of acetic acid in the mulch. The acid build-up is toxic to plants, and if the mulch is spread on the landscape without treatment, the volatile acid will quickly cause plants to wilt and subsequently die. Sour mulch can be treated by spreading it out thinly, soaking it with water, and allowing it to dry. After a few days of airing out, the smell should be gone and the mulch is safe to spread around plants.
Recycled Wood Product Mulches
Some companies recycle discarded wood and wood-based products by shredding them and adding a coloring agent to make them appear suitable for use in the landscape. These commercially produced mulches may decompose faster than natural bark mulches and may contain undesirable substances for use in vegetable gardens and children’s play areas.

Revised by UConn Home and Garden Education Center 2016.
Issued in furtherance of Cooperative Extension work, Acts of May 8 and June 30, 1914, in cooperation with the U.S. Department of Agriculture, the Dean of the College, Cooperative Extension System, University of Connecticut, Storrs. The Connecticut Cooperative Extension System is an equal opportunity employer and program provider. To file a complaint of discrimination, write USDA, Director, Office of Civil Rights, Room 326-W, Whitten Building, Stop Code 9410, 1400 Independence Avenue, SW, Washington, DC 20250-9410 or call (202) 720-5964.

Sulphate of Ammonia

Sulphate of Ammonia is a nitrogen rich fertiliser that promotes rapid greening in plants and lawn. It is especially effective in leafy plants and vegetables etc.

Sulphate of Ammonia is also used as an effective treatment for killing lawn clover.


Sulphate of Ammonia can be applied every 6 weeks from early spring to early autumn.
For a dry application, evenly spread 15g per square metre over the soil or existing lawn, and water in well.

For a liquid application, dissolve 30g of Sulphate of Ammonia per 5 litres of water in a watering can. This will cover 2 square metres of lawn or garden soil. It is still important to continue watering after application to avoid burning.

To kill clovers, heavily cover the clovers with a dry application of Sulphate of Ammonia. Allow the Sulphate of Ammonia to sit for between 12 to 24 hours, (preferably in hot weather) before watering heavily into the soil. This will begin to burn the clover.

Continue watering the soil daily as the clover burns off. Please note that the surrounding lawn in contact with Sulphate of Ammonia will also burn. However with continued watering, the lawn will quickly return even stronger than before the clover took over.

North Dakota State University

In addition, erosion carries fine particles of soil that are enriched with nutrients. Eroded soil particles with attached nutrients will accumulate as sediment in water resources and serve as a source of available nutrients during long periods of time.

Oxygen Depletion

When manure or commercial fertilizers enter surface water, the nutrients they release stimulate microorganism growth. The growth and reproduction of microorganisms reduce the dissolved oxygen content of the water body.

Without sufficient dissolved oxygen in surface water, fish and other aquatic species suffocate. The resulting dead fish and other aquatic species degrade the water quality and cause unpleasant odors.

Eutrophication (algal blooms) in Big Mallard Marsh. (Photo courtesy of North Dakota Department of Health)

Weed Growth and Algae Blooms

The number of plants and algae in a lake, pond or other water body increase with an increased supply of nutrients, particularly N and P. N and P are present in manure in sufficient quantity to be used as fertilizer for crop growth and will have a similar effect on algae and aquatic plants. As with crops, nutrient availability is the critical factor in the growth of aquatic plants and algae.

The nutrient present in the least amount for growth will limit the production in the aquatic system. Introduction of even small amounts of the limiting nutrient to crops or aquatic systems can increase production substantially. In the case of agricultural crops, this is a good thing.

However, increased production of aquatic plants and algae is not healthy for water resources. Eutrophication is the term used to describe the natural or human-accelerated process whereby a water body becomes abundant in aquatic plants and low in oxygen content.

As these aquatic plants die, microorganisms use the organic matter as a food source. Once again, the microorganisms grow and reproduce and use up the oxygen in the water. Any increase in the amount of aquatic plant growth ultimately will result in a reduced dissolved oxygen content of the water body, eventually suffocating fish and other aquatic species.

A fish kill in North Dakota. (Photo courtesy of North Dakota Game and Fish Department)

In addition to oxygen depletion, the potential exists for the algae to be toxic. Blue-green algae (cyanobacteria) can cause rashes, nausea and respiratory problems in humans and has been documented that it kills livestock that drink from affected water storages. See the NDSU Extension publication “Cyanobacteria Poisoning (Blue-green Algae” for more information.

Ammonia Toxicity

Ammonia-contaminated runoff from fresh manure application sites is toxic to aquatic life. At high levels, ammonia in surface water will kill fish. Fish are relatively sensitive to ammonia in water. Concentrations as low as 0.02 parts per million (ppm) may be lethal. Surface water that manure impairs also may experience changes in species diversity because of ammonia toxicity.

Fecal Organisms

The fresh manure from warm-blooded animals has countless microorganisms, including bacteria, viruses, parasites and fungi. Some of the organisms are pathogenic (disease causing), and some of the diseases that animals carry are transmittable to humans, and vice versa.

Many states use fecal coliform bacteria as an indicator of pollution from warm-blooded animals, including humans. The test for fecal coliforms is relatively simple and inexpensive, compared with testing for specific pathogens.

Some fecal coliforms can be found in natural water sources, even without the influence of humans or their domestic animals. Birds, beaver, deer and other wild animals contribute fecal coliforms to surface water directly or in runoff.

Contamination from runoff and natural deposition are not the only ways for water to become impaired. If manure applications are mismanaged near wells, the risk of bacterial contamination of the groundwater via the well is greatly increased. Therefore, avoid surface application of manure where it can come into direct contact with a well or other drinking water supply. In addition, when grazing near surface water sources, take measures to restrict livestock use.


High levels of nitrates can be toxic to livestock and humans. Nitrates are not adsorbed to soil materials, so they may leach to groundwater. In some instances, stored or land-applied manures or nitrogen fertilizers have caused high concentrations of nitrates in water. Because nitrates freely leach down through the soil profile, nitrogen that is not used for crop or plant growth can reach the groundwater easily.

Nitrate in itself is not toxic to animals, but at elevated levels, it causes a disease called nitrate poisoning. See the NDSU Extension publication “Nitrate Poisoning of Livestock” for more information.

High levels of nitrates in drinking water are known to cause methemoglobinemia (blue-baby syndrome) in human infants and other warm-blooded animals. In humans and livestock, nitrates interfere with oxygen uptake in the circulatory system.

Odors and Gases

Manure odors can be a nuisance for nearby neighbors and communities. Constant nuisance odors can degrade the quality of life for anyone subjected to them. In addition, people have a wide range of susceptibility to health effects from odors.

Gases are emitted from facilities throughout the year but are released at the highest rates during agitation, pumping and application of liquid manure systems or during cleanout and application of solid manure systems. Volatilization of ammonia to the atmosphere may become a water quality problem near animal production facilities when it is returned to the earth dissolved in rainfall.


If managed properly, fertilizers and animal manures benefit crop production without causing environmental problems. In any management scenario, the manager must be aware of the possible negative consequences of mismanagement.

For additional information on water quality, see these other NDSU Extension Service publications:

  • “Phosphorus Behavior in the Environment”
  • “Nitrogen Behavior in the Environment”

Natural Resources Conservation Service

The Smell of Living Soil

By Sheila Keeling, NRCS Natural Resource Planner in the Hopkinsville, KY Work Unit

Have you ever thought about the feeling when you take off your shoes and dip your feet into a clear rippling stream?…….when you walk through a pile of fallen dried leaves or listen to the wind rustling through the tree leaves?…… when you watch the waves come into the shore over and over again?…. or when you smell the sweet fresh fragrance of earth? We feel something deep in the smell of that fresh-soil, and it is one of those mysteries that takes us back to a place in time. The smell of soil invokes something so deep that it never really can be described. Can you describe the smell of soil in a forest, freshly tilled field, or in a swamp? Have you ever wondered if fresh tilled soil has always had the same sweet aroma?

Actually it’s not the soil we smell but the bacteria that enters the soil through the geosmin. It’s the bacteria that is producing the chemical that we smell. The smell will be different depending on where the soil is found. Healthy, productive soils should smell fresh, clean and pleasant or have little odor at all. If the soil smells like ammonia or has a rotten odor that is a good indication there is poor drainage or lack of oxygen in the soil.

The unique smell is because soil is not just dirt. Healthy soil is living and is a complex ecosystem with an abundance of bio-diversity. “Land, then, is not merely soil; it is a fountain of energy flowing through a circuit of soils, plants, and animals”. Aldo Leopold, A Sand County Almanac, 1949. Soil…..”the Latin name for man, homo, derived from humus, the stuff of life in the soil.” Dr. Daniel Hillel

So when we smell that sweet fragrance of soil and feel something deep remember the soil is alive and ultimately it’s the soil that gives us life. Smell the soil we create.

(Photo credit: Marty Lewis, Soil Conservationist, Hopkinsville Work Unit)

The smell of the soil

‘You speak like the very spirit of earth, imbued with a scent of freshly turned soil’
The Hall of Fantasy by Nathaniel Hawthorne

‘And scent of earth, sweet with the evening rain…’
All Round the Year by Edith and Saretta Nesbit

Just what is the scent that inspires such celebratory descriptions? The chemical responsible has been given the name ‘geosmin’. In the last few decades we have learnt not only its molecular structure, but also its microbial and biochemical origins. It has turned out that geosmin must have perfumed the soil that first began to cover the land half a billion years ago, thanks to the activity of the earliest Streptomyces bacteria.

Animals as diverse as flies and humans are incredibly sensitive to geosmin, so its perception probably evolved very early in the emergence of primitive animals.

The evocative smell of freshly disturbed or wetted soil was first studied scientifically towards the end of the 19th century, when French biochemists Berthelot and André succeeded in extracting ‘l’odeur propre de la terre’; but it was not until 1965 that the Americans Gerber and Lechevalier tracked down the main odour component to a single compound, which they called geosmin . Gerber finally published the structure of geosmin in 1968. It is a member of the extensive family of terpenoid oils that are natural odours, flavours and signalling molecules (more than 70,000 naturally occurring terpenoids have been discovered). The sensitivity of diverse animals to geosmin is astonishing: it is reported that humans – not famous for their olfactory virtuosity – can smell it at levels as low as 100 parts per trillion.

The ability to make geosmin is an ancient bacterial trait

By the time that geosmin was chemically characterised it was well established that its major source in soil was bacteria of the genus Streptomyces. These abundant and complex bacteria grow like fungal moulds as a mycelium of branching thread-like hyphae, playing a very important part in the recycling of vegetable matter. Echoing fungal moulds, they reproduce by sending up aerial hyphal branches that bear spores. Geosmin is associated with Streptomyces spores, which are present in huge numbers in many soils. We can safely assume that the time-traveller visiting the planet as it was about 440,000,000 years ago would recognise the familiar smell of soil, as the earliest land plants collaborated with the first streptomycetes to generate protocompost.


Some other bacteria that are very unlike streptomycetes produce geosmin too. They include some myxobacteria, which roam the soil in swarms consuming other bacteria, before building elaborate multicellular fruiting bodies big enough to be visible to the naked eye. Geosmin is also produced by many cyanobacteria: photosynthetic bacteria well known as the agents of toxic blue-green scums, inaccurately called ‘algal blooms’, on recreational waters. Clearly, the production of geosmin and other earthy odours preceded the origin of streptomycetes, since the last common ancestor of these diverse geosmin-producing bacteria probably existed more than two billion years ago. Geosmin is also made by some soil-dwelling eukaryotic organisms, including some fungal moulds (notably Penicillium species), and beetroots, which owe their characteristic earthy taste to geosmin.

Geosmin and countless other terpenoids are made by variations on the same biosynthetic route

Although geosmin is not needed for basic cellular physiology, some other terpenoids are involved in such essential functions as electron transport, bacterial cell wall biosynthesis, sterol biosynthesis and photosynthesis. All terpenoids are made from the universal acyclic precursors geranyl diphosphate, farnesyl diphosphate, or geranylgeranyl diphosphate. These are themselves made by the condensation of the 5-carbon precursors dimethylallyl diphosphate (DMAPP) and isopentenyl diphosphate (IPP) in the ratios 1:1, 1:2 and 1:3, respectively. Usually only one appropriate synthase enzyme is needed to convert geranyl diphosphate into a particular monoterpenoid, farnesyl diphosphate into a certain sesquiterpenoid (meaning “one-and-a-half monoterpenoids”), or geranylgeranyl diphosphate into a specific diterpenoid. These enzymes catalyse what may be the most complex transformations mediated by any class of enzymes in all biology, typically changing the linkage and hybridisation states of more than half of the carbon atoms in their substrate.

The first sesquiterpene synthase to be studied was that involved in making pentalenolactone, an unusual antibiotic made by a few streptomycetes. Studies led by David Cane at Brown University, USA, established many of the key features of the enzyme’s action. When UK and Japanese scientists determined the first genome sequences of streptomycetes, several genes related to the pentalenene synthase gene were found. In the hope of finding the determinant(s) of geosmin production, mutations were introduced into these genes in the model organism Streptomyces coelicolor, and indeed one of the mutants could no longer make geosmin. The relevant gene encodes a geosmin synthase with two distinct pentalenene synthase-like domains, one of which converts farnesyl diphosphate into the sesquiterpene germacradienol. The other domain then converts germacradienol into geosmin. The genes responsible for geosmin synthesis in myxobacteria and cyanobacteria are homologous with the Streptomyces genes, consistent with the idea that they have a common origin in an ancient progenitor of these diverse bacteria that lived nearly three billion years ago.

S. coelicolor additionally produces a monoterpene, methylisoborneol, that also contributes to earthy odours. Two adjacent genes determine methylisoborneol synthesis, in which geranyl diphosphate is first methylated, and then cyclised. A third odorous sesquiterpenoid, albaflavenone, which has antibiotic activity, results from the activity of another gene pair in S. coelicolor. One of the genes encodes a terpene cyclase that acts on farnesyl diphosphate to make the tricyclic epi-isozizaene, and the other encodes a cytochrome P450 that oxidises epi-isozizaene to generate albaflavenone. This gene pair, like the methylisoborneol genes, occurs in about half of streptomycetes (most often, streptomycetes have one or the other pathway). It is curious that genes for Streptomyces antibiotics are usually of much rarer occurrence than the albaflavenone genes, suggesting that albaflavenone may benefit the producing organisms in a different way from most antibiotics, but perhaps similar to that of methylisoborneol.

The dramatic increase in understanding of terpenoid synthases has been exploited in the case of epi-isozizaene synthase, the hydrophobic active site contour of which has been remoulded to change the profile of products, giving rise to hopes that the knowledge-based manipulation of such enzymes may be exploited in the production of biofuels.

How ancient and pervasive is the ability of animals to sense geosmin?

Sensing of geosmin has recently been studied in detail in the fruit fly Drosophila melanogaster. The ability of fruit flies to detect geosmin is exquisite, and they hate the smell – so much so that it overrides the attraction of the flies to all known food sources. This extreme chemorepulsion is mediated by a dedicated neural connection to the brain from specific geosmin sensors, and allows flies to avoid food sources contaminated by micro-organisms toxic to them and their larvae. Since humans are also so good at detecting geosmin, it seems very likely that this ability (and hence the possession of geosmin receptors) is very widespread among all animals, perhaps sometimes serving to attract and sometimes to repel. In his 2007 book Streptomyces in Nature and Medicine, past Microbiology Society President, Sir David Hopwood, entertainingly rehearsed speculations about the detection of geosmin by animals, ranging from primitive worms and arthropods that use the producing micro-organisms as a food source, to camels looking for water in the desert. The animals would then convey the geosmin-producing organisms to new locations, either after passage through the vector’s gut, aided by the ability of the tough spores to withstand digestion, or carried externally. In Sir David’s words, “this is such a nice idea; let’s hope it turns out to be true”. A 1978 American study showed that a Streptomyces that causes potato scab was present on, and in, soil arthropods associated with the infected potatoes. Whether notions of geosmin attracting animals are true or not, they have not depended on modern scientific advances: in 1903 the American writer Mary Austin wrote, in The Land of Little Rain, “the coyote is your true water-witch, one who snuffs and paws, snuffs and paws again at the smallest spot of moisture-scented earth until he has freed the blind water”. As outlined previously, geosmin was evidently being produced two to three billion years ago, before the emergence of eukaryotes (ca. two billion years ago), let alone of multicellular animals (ca. 600,000 years ago). It is therefore quite plausible that geosmin sensing by animals may have had a single evolutionary origin in an ancient universal common ancestor.

Perfumiers have found geosmin an irresistible component of some of their concoctions, either as a purified commercially available product (as a 1% solution) or, as in the case of a more traditional potion, Mitti Attar, by distilling sun-baked earth with sandalwood (it is said to resemble the smell of the first monsoon rain on parched soil). For example, in the perfume The Smell of Weather Turning by the cosmetics company Lush, “geosmin is supported by oak wood, hay, beeswax, nettle, English peppermint, mint and Roman chamomile”. On the other hand, geosmin also has a considerable nuisance value, sometimes being the cause of off-tastes in water, wine and freshwater fish – there is a considerable library of research papers devoted to these aspects. It may also contribute to the smells generated during the large-scale industrial culture of streptomycetes for the production of antibiotics. Annoyance to nearby communities might perhaps be mitigated by the use of molecular genetic techniques to disrupt the geosmin synthase gene.


John Innes Centre, Norwich NR4 7UH, UK


Cane, D. E. & Ikeda, H. (2012). Exploration and mining of the bacterial terpenome. Acc Chem Res 45, 463–472.

Li, R. & others (2014). Reprogramming the chemodiversity of terpenoid cyclisation by remolding the active site contour of epi-isozizaene synthase. Biochemistry 53, 1155–1168.

Stensmyr, M. C. & others (2012). A conserved dedicated olfactory circuit for detecting harmful microbes in Drosophila. Cell 151, 1345–1357.

Yamada, Y. & others (2015). Terpene synthases are widely distributed in bacteria. Proc Natl Acad Sci U S A 112, 857–862.

Would that you could inhale the aroma of summer rain falling on a long, hot day in Sarasota, Florida. It smells sweet like grass, earthy like soil, lush, a touch salty, fresh, and green—like relief.

Indeed, anthropologist Diana Young of the University of Queensland in Australia believes that we, and other creatures, evolved to respond positively to the scent of rain as a sign of flourishing life. Young studies the culture of Western Australia’s Pitjantjatjara people, and has observed that they associate the smell of rain with the color green—a visual and olfactory link between aroma and the expectation of growth. She calls this sensual blend “cultural synesthesia,” and says we all share it.

The precise aroma of falling rain differs from place to place, season to season, even from one rainfall to another. The scent of rain has been bottled in India since 1911. It’s called “mitti attar,” or Earth’s perfume, and is made from distilling the essence of monsoon-soaked soil. That scent is different from rain cooling a hot sidewalk in New York City, which is in turn distinct from the drops falling on sand, in a grassy field, a forest, or by the sea. The smell of a storm accompanied by lightning is sightly metallic, for example, as oxygen and nitrogen molecules in the atmosphere combine into nitric oxide, while a gentle rain in the woods is rich and fungal.

Yet the scent of rain, particularly after a long dry spell, is pleasing to all, humans and animals alike, in all the places. And, despite countless variations, it goes by a single name—petrichor.

The blood of gods

The word petrichor was invented by two Australian scientists who introduced it in a 1964 paper on the Nature of Argillaceous Odor (pdf), an investigation into the scent of moistened clay, rock, and sediment. They combined the Greek word for stone, “petra,” and “ichor,” which means “the blood of gods”, to coin a name for the scent of rain.

The mineralogists posited that the scent released by rain isn’t that of water, which itself has no odor, but is actually the aroma of organic compounds accumulated in the atmosphere and on surfaces; these are released when rain falls. The compounds include bacteria called geosmin. These bacteria gives beets their earthy flavor and help make digging up soil in a garden so satisfying and soothing.

Rain also releases aromatic terpenes secreted by plants. Terpenes are hydrocarbons found in the essential oils of plants. They’re what makes a walk in greenery both fragrant and healing.

And when rain falls, geosmin and terpenes fly—or more precisely, they fizz.

Aerosol fizz

Technically speaking, the smells of these organic compounds are released via aerosol spritzes that result from rainfall, according to MIT researchers. When rain falls on a porous surface—say, caked clay, a dirt road, or a concrete slab—it traps tiny air bubbles at the point of contact. Those bubbles shoot upward and then burst into an aerosol fizz, like champagne.

What’s on the surface and in the air—the terpenes and bacteria of a particular area—and how long these compounds have accumulated there, dictates the precise scent and extent of aroma released by the rain, smells which are then carried by the wind. The velocity of the raindrop, along with porousness of the surface on which it falls, influences the aerosol spritz. Interestingly, more aerosol is released in light rain than during a heavy downpour, the researchers found.

Capturing a natural aroma

Because the scent of rain has so many variations depending on where and when it falls and how heavily, so do the many perfumes that claim to capture the natural phenomenon.

In fact, rain perfumes aren’t bottled raindrops. They are combinations of earthy or floral blends that are reminiscent of the different aerosol fizzes released by raindrops around the world at different elevations, falling on distinct surfaces where a range of plants and bacteria grow.

Probably the purest among these is the Earth perfume made in India of distilled monsoon soils for more than a century. Newer takes include Thunderstorm, a scent by Demeter, that attempts to capture the “‘deep and violent” scent of a summer storm brewing, when humidity on the ground exceeds 75% and the smell of petrichor is most poignant.

Meanwhile, perfumer Christopher Brosius composed a scent called Black March, reminiscent of “rain drops, leaf buds, wet twigs, tree sap, bark, mossy earth, and the faintest hint of spring.” Brosius uses beet extract—rich in geosmin—to conjure up a rich, earthy aroma. The scent is named after a Stevie Smith poem, says Brosius, which begins, “I have a friend at the end of the world. His name is a breath of fresh air.”

Perfumer David Seth created a scent inspired by a hike in northern Ireland, called Pale Grey Mountain, Small Black Lake. It would surely have captured the hearts of the Australian mineralogists who coined the term petrichor, as Seth describes the scent as “fog-on-stone.” The perfume attempts to captures all the elements of an aromatic storm—petrichor, geosmin, and ozone. He told Into the Gloss, “I was trying to take that fresh-wet effect and weave it into the narrative of what happened . So I made some steely accords of grey rocks—ambergris, thin woods, and metallic/ozonic aldehydes—and added watery materials like ozonic and radiant materials to them.”

Naturally nostalgic

Attachment to the scent of rain is like an ancient memory we’re already born with. It’s in our genes. We feel it deeply, perhaps just like our ancestors did, even though most of us are no longer connected with the earth very closely and don’t grow our own food or livestock.

Although we’re not necessarily conscious of it, the scent conjures an ancient promise of plenty, and so we long to breathe it in deeply. It makes us nostalgic, naturally.

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