Removing nitrogen from soil

Are your plant leaves looking burnt? Nitrogen heavy soil can be just as detrimental to plants as having lack of nitrogen. In this article, we explore 5 simple ways to help reduce nitrogen in your soil so you can get you garden back to a healthy, balanced level of nutrients.

Effects of high Nitrogen levels in your soil

Effects of high nitrogen in your soil can be visually identified by taking a close look at your plants. Here are some common effects of high nitrogen in your soil:

  • Foliage overgrowth – the plants are redirecting energy into only producing excess foliage.
  • Restricted flower growth – It may restrict the production of your plants reproductive organs(flowers) which produces the fruit and vegetables you are looking for. You will end up with a lot of green, but no vegetables or fruits.
  • Stunted root growth – If all the plants energy is focused above the soil in creating new foliage and green growth, the roots will be ignored and plant stability can be compromised, which can invite disease.
  • Burnt foliage – Leaf edges will appear wilted and start turning yellow and brown and will eventually destroy the plant.

Tips On How To Reduce Nitrogen In Soil

While there are many ways to help reduce excess nitrogen symptoms, most will require some patience but will guarantee that nitrogen is removed from your soil. Below are 5 methods to reduce nitrogen in your soil:

  1. Add sawdust or fine woodchips to your soil – the carbon in the sawdust/woodchips love nitrogen and will help absorb and soak up and excess nitrogen.
  2. Plant heavy nitrogen feeding plants – tomatoes, corn, broccoli, cabbage and spinach are examples of plants that thrive off nitrogen and will suck the nitrogen dry.
  3. Water – soaking your soil with water will help leach the nitrogen deeper into your soil, effectively leaving less for your plants to use.
  4. Sugar – In limited studies, it was shown that adding sugar to your soil can help potentially reduce the amount of nitrogen is your soil. Sugar is partially composed of carbon, an element which attracts and soaks up the nitrogen in the soil. This is similar concept to adding sawdust/woodchips which are high in carbon content.
  5. Do nothing – It may seem counter-intuitive, but if you already have plants that are producing lots of foliage, it may be best to let them continue to absorb all the nitrogen to amend the soil for your next crops.

As I state in most of my soil articles, the only way that you can surely be aware if you have excess nitrogen in your soil is to perform a soil test. If you are looking to purchase one to ensure your soil is in good health, I strongly suggest this soil test kit. Its cheap, effective, and gets the job done.

If you have any questions about gardening or issues that your dealing with, leave a comment below and I’ll get back to you ASAP. I’m always here to help!

Nitrogen is one of the three most important so-called “macronutrients” for the healthy growth of plants, along with its equally important cousins phosphorus and potassium. These three elements are the central components of most fertilizers, and they form the N-P-K ratio that is shown on fertilizer packaging. A good, balanced, organic fertilizer for general garden use might have an N-P-K ratio of 4-4-4, as does the outstanding All Purpose Blend from Gaia Green.

One of the most common problems we hear about in the garden, and not just from beginners, is the presence of too much nitrogen. This element is fundamental to the growth of leaves and plant tissue, and an important food for the many soil organisms that convert other nutrients into forms that are available to plants. Nitrogen is also a component of chlorophyll, so it is central to basic photosynthesis, and therefore needed by all plants. A lack of nitrogen might result in plants that were stunted and yellowy, with withered growth and overall poor health.

However, when too much nitrogen is present, what tends to result is an explosion of foliar growth, but at the expense of flower formation, fruit set, and root growth. It’s not uncommon to hear about really vigorous beets or carrot tops, where the vegetables produce lush, unruly, abundant leaves, but no root to speak of. We have heard about pea plants that seem to race skyward, but then produce few flowers that are followed by disappointingly few peas.

How does it happen?

Gardeners and growers like to prepare their soil at the start of the season by applying mulch, manure, cover crops, and/or fertilizer. For a crop of sunflowers (for instance) to grow twelve feet tall, with massive leaves and a giant seed head in just three or four months, the plant needs to draw an amazing amount of nutrients from the soil. Whatever crop is harvested at the end of the season, masses of soil nutrients come with it. So gardeners and growers have a genuine need to cultivate healthy, fertile soil for good crop results.

Some of those soil amendments and fertilizers can be excessively high in nitrogen. One common example is animal manure that has not been fully composted. We have heard of people planting into pure, undiluted Sea Soil. Some organic soil amendments like feather meal (a byproduct of chicken and turkey rendering), has an N-P-K ratio of 15-0-0, so it is pretty much pure nitrogen. Chemical nitrogen is also available in the form of ammonium nitrate — this highly unstable chemical was once the go-to form of fertilizing commercial fields, but that’s a bit off topic… Usually, it is the application of some sort of well-intended soil amendment that produces the problem of excess nitrogen.

How to fix it?

Of all three macronutrients, nitrogen is the quickest to become depleted in soil. Water from winter rain and snow washes a tremendous amount of it away. De-nitrifying bacteria consume available nitrogen and further deplete soil. And heavy agricultural use of soil also sucks out much of the available nitrogen.

Perhaps the best way to take advantage of a soil that is discovered to be nitrogen heavy is to simply plant crops that thrive on nitrogen. Leafy greens of all sorts, including nearly all crops that are not harvested for roots (like carrots), shoots (like broccoli), or fruits (like peppers & beans), need nitrogen more than they need phosphorus and potassium. Kale, pac choi, mustards, lettuce, spinach, and most chicories would be good candidates for nitrogen rich soil.

By contrast, it’s those crops that produce roots, shoots, and fruits that are the most likely to struggle when nitrogen levels are excessive.

The notion of trying to bring the three macronuntrients into balance by bringing up the phosphorus and potassium levels would likely cause more problems than it would solve. A preferable method would simply be to let the soil rest. Apply a mulch of organic material, like leaves, and give the soil some time to come back into a natural balance. Then, when it’s time to plant again, be sure that any fertilizer inputs have that balanced ratio like the 4-4-4.

Want to know more about? Read our article, “What the Heck is N-P-K?”

Management of Nitrogen and Phosphorus

. . . an economical use of fertilizers requires that they merely supplement the natural supply in the soil,and that the latter should furnish the larger part of the soil material used by the crop.


Both nitrogen and phosphorus are needed by plants in large amounts, and both can cause environmental harm when present in excess. They are discussed together in this chapter because we don’t want to do a good job of managing one and, at the same time, do a poor job with the other. Nitrogen losses are a serious economic concern for farmers; if not managed properly, a large fraction (as much as half in some cases) of applied N fertilizer can be lost instead of used by crops. Environmental concerns with N include the leaching of soil nitrate to groundwater; excess N in runoff; and losses of nitrous oxide, a potent greenhouse gas. For P, the main concerns are losses to freshwater bodies.

High-nitrate groundwater is a health hazard to infants and young animals because it decreases the blood’s ability to transport oxygen. In addition, nitrate stimulates the growth of algae and aquatic plants just as it stimulates the growth of agricultural plants. The growth of plants in many brackish estuaries and saltwater environments is believed to be limited by a lack of N. So, when nitrate leaches through soil, or runs off the surface and is discharged into streams, eventually reaching water bodies like the Gulf of Mexico or the Chesapeake Bay, undesirable microorganisms flourish. In addition, the algal blooms that result from excess N and P cloud water, blocking sunlight to important underwater grasses that are home to numerous species of young fish, crabs, and other bottom dwellers. The greatest concern, however, is the dieback of the algae and other aquatic plants. These plants settle on the bottom of the affected estuaries, and their decomposition consumes dissolved oxygen in the water. The result is an extended area of very low oxygen concentrations in which fish and other aquatic animals cannot live. This is a serious concern in many estuaries around the world.

Table 19.1: Comparing Soil N and P
Nitrogen Phosphorus
Nitrogen becomes available from decomposing soil organic matter. Phosphorus becomes available from decomposing soil organic matter and minerals.
N is mostly available to plants as nitrate (NO3 )—a form that is very mobile in soils P is available mainly as dissolved phosphate in soil water—but little is present in solution even in fertile soils, and it is not mobile.
Nitrate can be easily lost in large quantities by leaching to groundwater or by conversion to gases (N2, N2O). P is mainly lost from soils by runoff and erosion. However, liquid manure application on well-structured soils and those with tile drainage has resulted in P loss to drainage water.
Nitrogen can be added to soils by biological N fixation (legumes). No equivalent reaction can add new P to soil, although many bacteria and some fungi help make P more available to plants.

Denitrification is a microbial process that occurs primarily in surface layers when soils are saturated with water. Soil bacteria convert nitrate to both nitrous oxide (N2O) and N2. While N2 (two atoms of nitrogen bonded together) is the most abundant gas in the atmosphere and not of environmental concern, each molecule of N2O gas—largely generated by denitrification, with some contribution from nitrification—has approximately 300 times more global warming impact than a molecule of carbon dioxide.

Phosphorus losses from farms are generally small in relation to the amounts present in soils. However, small quantities of P loss have great impacts on water quality because P is the nutrient that appears to limit the growth of freshwater aquatic weeds and algae. Phosphorus damages the environment when excess amounts are added to a lake from human activities (agriculture, rural home septic tanks, or urban sewage and street runoff). This increases algae growth (eutrophication), making fishing, swimming, and boating unpleasant or difficult. When excess aquatic organisms die, decomposition removes oxygen from water and leads to fish kills.

All farms should work to have the best N and P management possible—for economic as well as environmental reasons. This is especially important near bodies of water that are susceptible to accelerated weed or algae growth. However, don’t forget that nutrients from farms in the Midwest are contributing to problems in the Gulf of Mexico—over 1,000 miles away.

There are major differences between the way N and P behave in soils (figure 19.1, table 19.1). Both N and P can, of course, be supplied in applied fertilizers. But aside from legumes that can produce their own N because of the bacteria living in root nodules, crop plants get their N from decomposing organic matter. On the other hand, plants get their P from both organic matter and soil minerals. Nitrate, the primary form in which plants absorb nitrogen from the soil, is very mobile in soils, while P movement in soils is very limited.

Most unintentional N loss from soils occurs when nitrate leaches or is converted into gases by the process of denitrification, or when surface ammonium is volatilized. Large amounts of nitrate may leach from sandy soils, while denitrification is generally more significant in heavy loams and clays. On the other hand, most unintended P loss from soils is carried away in runoff or sediments eroded from fields, construction sites, and other exposed soil (see figure 19.1 for a comparison between relative pathways for N and P losses). Phosphorus leaching is a concern in fields that are artificially drained. With many years of excessive manure or compost application, soils saturated with P (often sands with low P sorption capacity) can start leaking P with the percolating water and discharge it through drain lines or ditches. Also, liquid manure can move through preferential flow paths (wormholes, root holes, cracks, etc., especially in clay soils) directly to subsurface drain lines and contaminate water in ditches, which is then discharged into streams and lakes (see also chapter 17).


There are quite a few reasons you should not apply more N than needed by crops. N fertilizers are now quite expensive, and many farmers are being more judicious than when N was relatively cheap. However, there are other problems associated with using more N than needed: (1) ground and surface water become polluted with nitrates; (2) more N2O (a potent greenhouse gas and source of ozone depletion) is produced during denitrification in soil; (3) a lot of energy is consumed in producing N, so wasting N is the same as wasting energy; (4) using higher N than needed is associated with acceleration of decomposition and loss of soil organic matter; and (5) very high rates of N are frequently associated with high levels of insect damage.

Except when coming from highly manured fields, P losses—mainly as dissolved P in the runoff waters—from healthy grasslands are usually quite low, because both runoff water and sediment loss are very low. Biological N fixation carried on in the roots of legumes and by some free-living bacteria actually adds new N to soil, but there is no equivalent reaction for P or any other nutrient.

Improving N and P management can help reduce reliance on commercial fertilizers. A more ecologically based system—with good rotations, reduced tillage, and more active organic matter—should provide a large proportion of crop N and P needs. Better soil structure and attention to use of appropriate cover crops can lessen loss of N and P by reducing leaching, denitrification, and/or runoff. Reducing the loss of these nutrients is an economic benefit to the farm and, at the same time, an environmental benefit to society. The greater N availability may be thought of as a fringe benefit of a farm with an ecologically based cropping system.

In addition, the manufacture, transportation, and application of N fertilizers are very energy intensive. Of all the energy used to produce corn (including the manufacture and operation of field equipment), the manufacture and application of N fertilizer represents close to 30%. Although energy was relatively inexpensive for many years, its cost has fluctuated greatly in recent years, as has the cost of fertilizers, and is expected to be relatively high for the foreseeable future. So relying more on biological fixation of N and efficient cycling in soils reduces depletion of a nonrenewable resource and may save you money as well. Although P fertilizers are less energy consuming to produce, a reduction in their use helps preserve this nonrenewable resource—the world’s P mines are expected to run out in the next fifty to one hundred years.

Chapter 18: Sources | Top | Management of N and P

If you garden, do lawn maintenance, or farm, you’ve probably added nitrogen fertilizer to your soil. Nitrogen is the most common nutrient to limit plant growth – because plants need quite a lot of it (10-60 g per kg of plant mass, to be exact). It also doesn’t stick around very long in the soil. Instead, it ends up in places where we don’t want it: in groundwater, water bodies, and even the atmosphere.

But, why? And how can we get nitrogen to stay in the soil, where plants need it?

Keep nitrogen in your yard by following these tips. Infographic: SSSA staff

To answer that question, we need to take a closer look at the nitrogen cycle. The nitrogen cycle, in which nitrogen moves through soil, water, air, and organisms, is one of the most complex element cycles. Luckily, keeping nitrogen in the soil simply involves reducing the losses of nitrogen from the soil. Losses are ways that nitrogen exits the soil.

To keep nitrogen in soil, we need to reduce 4 key losses:

  1. Leaching
  2. Ammonia volatilization
  3. Denitrification
  4. Harvesting


Leaching happens when water travelling through the soil dissolves nutrients from the soil, and carries them downwards into the groundwater table. Leaching losses are largest in wet climates, especially regions with enough rainfall to support plant growth year-round. In the United States, for example, wetter regions east of the Mississippi River have much higher leaching losses than drier regions in the Southwest. In wetter areas, about 30% of nitrogen fertilizer is lost due to leaching. This leached nitrogen contributes to pollution in groundwater, lakes, rivers, and even the ocean.

How can I reduce leaching? Leaching losses are greatest following rainfall or irrigation. So, reducing them is mostly a matter of timing. If rain is in the forecast, wait until after it rains to apply nitrogen fertilizer (a little drizzle won’t matter, but watch out for steady rain or thunderstorms). If rain is a long way off, say a week or more, it is ok to apply fertilizer ahead of time. The type of fertilizer also matters. Nitrate doesn’t “stick” well to soil, and so it is lost very easily. To reduce leaching losses, avoid nitrate (NO3–) fertilizers, and instead choose ammonium (NH4+) or organic fertilizers (including urea, composts and manures).


Ammonia volatilization happens when ammonium (NH4+) loses a hydrogen (H+) and becomes ammonia (NH3). Ammonia is a gas, and so it can rapidly leave the soil to pollute the atmosphere. Ammonia volatilization is most likely to happen in alkaline soils (pH > 7) and when the soil is warm.

How can I reduce ammonia volatilization? Avoid applying ammonium fertilizers, composts, and manures on warm to hot days – especially if your soil is alkaline.


Denitrification is a multi-step process where microbes convert nitrogen (in nitrate form, NO3–) into various nitrogen gases. One of these gases is nitrous oxide, N2O, a potent greenhouse gas. The other is nitrogen gas, N2, which is harmless and comprises 79% of the atmosphere. Denitrification happens when the soil gets very wet and stays wet for several hours to days. In very wet soil, microbes can’t get enough oxygen (O2). So, microbes “breathe in” nitrate instead of oxygen, and “breathe out” nitrogen gases (N2O and N2) instead of carbon dioxide (CO2).

Prevent leaching and denitrification by checking the weather forecast for clear weather for 48 or more hours before you fertilize your lawn or garden. Credit: Morguefile

How can I reduce denitrification? Similar to preventing leaching losses, avoid applying nitrate fertilizers before rainfall, and when the soil is very wet. Instead, use non-nitrate fertilizers, especially if the soil is saturated. When using any kind of nitrogen fertilizer, apply when the soil is dry to somewhat moist, and when the forecast is rain-free for the next few days. This will give the nitrogen time to be taken up by plants and “stick” to the soil before it rains. That way, denitrifying microbes growing in wet soil won’t have as much nitrate to “breathe in.”


Harvest losses are exactly what they sound like – nitrogen that is lost when crops are harvested. Plants take up nitrogen from the soil, and when the plant is harvested and removed from the soil, the nitrogen is removed with it.

How can I reduce harvest losses? You can reduce harvest losses by only harvesting the part of the plant you need to eat, and turning the rest into mulch or compost. You can also collect the non-edible plant parts after harvesting, and return those to the soil. For example, instead of throwing green been stalks and trimmings in the trash, compost them first, and then add them to the soil.


Generally, increasing soil organic matter is a great way to improve nitrogen retention in the long term. Nitrogen “sticks” to organic matter, reducing both leaching and denitrification. Read this Soils Matter blog to learn how to keep more carbon – organic matter – in your yard.

Answered by Rivka Fidel, University of Arizona

Hydroponic gardening is wonderful for so many reasons, but we growers still run into problems from time to time. In fact, as a beginner there can be more problems than gardening in soil!

Nitrogen toxicity is one of these annoying problems. Nitrogen is one of the most important nutrients for plants, but too much can cause serious harm to your garden. If left unchecked, nitrogen toxicity can completely kill your plants.

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What is Nitrogen Toxicity?

Plants need a lot of nitrogen, especially in their vegetative stage of growth. Most of the time it’s hard to give them too much, but every now and then you can get too excited and flood your nutrient reservoir with excess nitrogen.

When that happens, your plants cannot handle the surplus and begin to struggle. This happens most often in the flowering stage of growth, when plants need less nitrogen than they did in earlier stages. If you keep nitrogen levels stable and don’t properly adjust your nutrient mixture, you could be setting your garden up for nitrogen toxicity.

How Much Nitrogen Does Your Plant Need?

Note: These are general rules of thumb, not specific prescriptions for particular types of plants. Every type of plant is different and requires a different mixture of nutrients for optimal growth. However, there are consistent patterns between all plants that you should know.

Vegetative Stage

During this stage, your plant will feast on nitrogen as it develops the stems, roots, and foliage to support energy production during flowering phase. Almost any type of hydroponic nutrient will do well here. If you are looking for recommendations, both General Hydroponics FloraNova Grow and Dyna-Gro Foliage Pro are great options.

Flowering / Blooming Stage

During this stage, your plants are transitioning from developing a lot of leaves and stems and focusing their energy on buds, flowers, and fruit. If you give your plants too much nitrogen during this phase you can seriously impact its development. Two good nutrient recommendations here are General Hydroponics FloraNova Bloom and Dyna-Gro Bloom. If you can’t source these locally or online, you can make do with a fertilizer designed for cacti, because they have similar nutrient requirements to a blooming plant.

Signs of Nitrogen Toxicity

An example of the opposite problem, nitrogen deficiency. If you take the “normal” appearance and darken it, you have a classic symptom of nitrogen toxicity.source

While the signs of nitrogen toxicity vary slightly based on the plant that you’re growing, there are some universal signals that point to nitrogen toxicity as the problem you’re facing:

  1. Extremely dark green leaves
  2. “Burning” of leaf tips, causing them to turn brown
  3. Some leaves turning yellow, due to abundance of nitrogen but lack of other nutrients

These symptoms are exacerbated if the pH of your solution is off or if you are over or under-watering your plant. All of these cause your plant to stress easier, making the effects of too much nitrogen more pronounced.

Ruling Out Other Potential Plant Problems

Before you jump to treating your plant for nitrogen toxicity, it’s a good idea to rule out any other potential causes.

First, make sure you aren’t over or under-watering your plant. If you’re growing hydroponically, you shouldn’t have to worry about this because the roots are likely sitting in a nutrient solution of some kind.

Make sure your nutrient solution is being properly oxygenated with air stones, and that the pH and temperature of your nutrient solution are within normal ranges.

Finally, check the air temperature of your grow tent or grow room and make sure it’s not too hot or cold.

If your garden passes all of these checks, it’s very likely you have a nitrogen toxicity problem and you can move on to treatment and prevention options.

Treating Nitrogen Toxicity

Nutrient burn in a tomato plant.

If you guessed that the solution to nitrogen toxicity is “stop giving your plants so much nitrogen,” you’d be right! But treating an existing garden suffering from nitrogen toxicity isn’t quite that simple, though it’s still pretty easy to fix.

Check the PPM / EC of your solution and ensure that is within normal ranges for your plant’s stage of growth. If it isn’t, you can:

  • Dilute the solution with fresh water, being sure to calibrate your pH afterwards
  • Change out your nutrient reservoir completely with fresh water and nutrients

If your plant is in flowering phase, nutrient levels look good, and you’re still suffering from symptoms of nitrogen toxicity, you should probably do a complete reservoir change and add fresh nutrients. It might be the case that you have too much nitrogen as a percentage of total nutrients in the solution, causing poor results during flowering phase.

If you’re growing in soil but don’t feel that you’re over-feeding your plants, you may just have soil that has a higher concentration of nitrogen than normal. To fix this, filter and pH some water and pour it in the soil that houses the affected plants. This will flush out some of the nutrient contents of your soil and hopefully solve the problem.

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Nitrogen Toxicity

Nitrogen Toxicity

Signs of Nitrogen Toxicity:

Plants that are showing signs of nitrogen toxicity will be affected differently at different stages of life for example young growth and young pants can show the telltale dark green leaves as well as a claw like look. But older plants that are in flower might have enough energy to use the nitrogen but produce smaller buds as nitrogen in flower as the effect of encouraging the plant to spend its energy producing leaves instead of flowers.

Common signs of Nitrogen Toxicity:

  • Dark green leaves and foliage
  • Leaf tips may turn down, without signs of overwatering.
  • You may notice yellowing on the affected leaves or other signs of nutrient deficiencies as time goes on
  • Nitrogen toxicity is often but not always accompanied by nutrient burn
  • Leaf Curl or the Claw will happen first to older leaves then move up the plant
  • Heat and pH problems will make the claw affect worse, as they stress out the plant and lower her defenses, and cause her to drink more water (and uptake more N)
  • As time goes on, the claw leaves will eventually start turning yellow, getting spots, and dying

If you start to notice these symptoms accompanied with slow growth or smaller flowers in your finished plants, then somewhere your plant is getting to much nitrogen.

This can simply be a result of over feeding and providing too much nutrients in the form of nitrogen to your plants. When dealing with nutrient toxicity, first steps are to:

  • Flush your media with 3-10 times its normal watering w/pH5.5(inert), pH 6.0(if in soil)
  • A day After a media flush, reintroduce low strength nutrients and then up the strength till full feed is possible
  • Do a pH test of run off along with soil pH test to determine if a pH issue exist there
  • Add more watering’s without feed to your feeding schedule if Toxicity is a reoccurring problem

If even flushing and lowering your nutrients do not have an effect on your nitrogen toxicity issue, then it might be time to look more closely at your media and main source of nutrients.

For soil user you will need to figure out how to increase soil bio diversity to either introduce microbes or remove them. If after a flush your media is still of its optimal pH values, 5.8-6.5, then something in your soil is producing that offset and introducing beneficial enzymes and bacteria/microbes will help.

If you are using a 1 part Veg and Bloom, try a 2 part or three part, if you are using 2 or 3 part just lower your feeding rates after a flush and slowly increase them over time. If the nutrient is separated into bloom and veg formulations follow the recommended feeding rates and times. Start low and then build up to full strength rates.

How to Fix Nitrogen Toxicity in No-Till? Excess Nitrogen is Attracting Aphids

I think my no till containers are nearing nitrogen toxicity and I am hoping to get some advice on how i can “back off N” in no-till? I think my plants are nearing nitrogen toxicity because not only are they darker green than what I’m use to but I’m seeing aphids on my plants. And I’ve read from countless sources that aphids will tend to gravitate towards plants that are excessive in nitrogen (the darker green plants).

WIth that being said, if i had to guess why I’m seeing nitrogen toxicity i would say its because i top dressed way too much vermicompost a couple months ago? would that most certainly do it?

I have a twenty gallon worm bin and i harvested half of it about two months ago so each of my six 25-gallon no-till container in my backyard got approximately 2 gallons of worm poop as a top dress. Other than that, I only top dress MBP, corn sprouts, and kelp and thats not even that often.

Well I’m ready to harvest half my worm bin now and am wondering if i should skip topdressing with vermicompost for a cycle maybe if i think i maybe nearing nitrogen toxicity?

I am outdoors so I am also wondering if i should let nature take care of the aphids like i do when it comes to other pests, outdoors? Or should I address the aphids directly by releasing some lady bugs?

So two questions:

  1. how do i back off N? Can I just skip a topdress of worm poop for the next cycle?

  2. should i simply let nature take care of the aphids on my outdoor plants? or do i need to address the Nitrogen issue? or do i release lady bugs?

What is Nitrogen Toxicity and How To Resolve It?

The above leaf shows early stage nitrogen toxicity. Excessive N has caused the leaf to turn extremely dark green, along with dark purple petiole visible.

Nitrogen toxicity is one of, if not the most common toxicity to experience in your plant. It is caused by too much vegetative fertilizer and can is easy to identify once its starts. Unfortunately, affected leaves do not resolve and only new growth will show that you’ve managed to equal out the soil. Nitrogen Toxicity is most common identified by the dark green shade of the leaves, this tends to be the first stage. As the toxicity continues, the leaves will begin to get a shiny glaze to them that makes them almost reflective. Stems can also turn dark shades of purple, though this isn’t always a sign of nitrogen toxicity and can also be part of the plants natural genetics.

Because autoflowers tend to require less nutrients than photoperiod plants, you may find that Nitrogen toxicity is a bit more common to experience than your photoperiod grows. Fortunately, it is quite easy to identify Nitrogen toxicity in early stages and to make the required changes to your feeding schedules.

Identifying Nitrogen Toxicity

  1. Look for leaves turning dark green. Nitrogen (N) is directly linked to chlorophyll levels and an increase in nitrogen results in darker leaves, while an N deficiency will result in leaves losing their green colouration. In the early stages of an N toxicity issue, you’ll first start to see leaves turning dark green, followed by an almost blue colouration if left untreated. Be sure to check your leaves in natural light (especially when running blurple LEDs), as it is easy to miss these initial signs when your plants all just look pink and purple.
  2. Look for darkening petiole. You can also monitor the petiole (stem leading up to the leaf) for colouration changes, though this method is a bit less reliable as some genetics cause the same purple colouration of the petiole.
  3. Look for clawing. One of the later stages of nitrogen toxicity results in clawing of the fan leaves. There are numerous conditions which can cause the leaves to claw, but nitrogen toxicity is one of the most common.

Later stage nitrogen toxicity showing reflective dark green leaf along with clawing.

How To Treat Nitrogen Toxicity

So you’ve found that your plant is getting too much nitrogen and you’re looking to fix the problem. Unfortunately, as touched on, leaves that have suffered from the effects of nitrogen toxicity don’t usually recover, however it is important to resolve the problem for any new growth on the plant.

If you’ve caught your nitrogen toxicity early on, when leaves are just showing exaggerated dark greens, you can simply adjust your feeding mix to offer less nitrogen based fertilizers. Though if your plants are showing severe issues you may wish to do a flush of your soil to ensure that you remove any possible build up of nitrogen in the medium. After flushing, resume feeding but with lower N.
It is vital that you check up on your plants for N toxicity regularly, for new growers they may think that the darker green leaves are something to celebrate, and the early signs of this problem may go unnoticed.

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