- How to Grow Vegetables in Clay Soils
- Vegetables That Grow In Clay Soil
- Why Clay Soil Is Frustrating?
- Improving clay soil
- Finally, here is my high-value list of the veggies to plant in clay:
- Final Round Up
- Transform Difficult Clay Into Gold
- Add Amendments
- Add Organic Compost
- Add Mulch
- How To Grow Vegetables In Your Clay-filled Backyard
- Characteristics Of, & Profile Of Clay Soil
- Working With, Improving & Amending Clay Soil
- A Note On Soil Types, & What Ultimately Impacts How Things Grow
- Plants & Flowers That Grow Well In Clay Soil
- Fruits & Fruit Trees That Grow Well In Clay Soil
- Vegetables & Crops That Grow Well In Clay Soil
- Trees, Shrubs and Bushes That Grow Well In Clay Soil
- Plants For Wet Clay Soil
- Best Cover Crops For Clay Soil: Fixing Clay Soil With Cover Crops
- Using Cover Crops to Improve Clay Soil
- Cover Crop Plants for Clay Soil
- Best Cover Crops for Clay Soil
- Using Cover Crops to Improve Soil and Water Quality
- Cover Crops – Protect and Improve Your Soil
- Additional Information
- Use Cover Crops to Improve Soil
- Cover crop for Clay soil?
- Garden Cover Crops
How to Grow Vegetables in Clay Soils
If you’re reading this, then you are probably well aware of the challenges of growing vegetables in clay soil. Clay is frustrating. Clay is heavy. Clay is, in the opinion of some, best left for throwing pots and not potting plants.
However, clay can also be a rich growing medium, if you know how to work it. Here are some tips for growing vegetables in clay soil to help you get your garden looking more like a garden, and less like the contents of a pottery studio.
The Benefits of Clay Soils
As difficult as clay is to work with, there are several important benefits that we need to remind ourselves of as we grow. Clay is rich in nutrients and holds nutrients and moisture well, thanks to its density. This means that you can take advantage of slow-release mineral fertilizers, like rock phosphate and gypsum, as you try and boost soil fertility.
Some vegetables even prefer clay. Lettuce, chard, snap beans, and vegetables with shallow root systems do well in clay soils thanks to its moisture retention capabilities. Cole crops like broccoli, cabbages, and Brussels sprouts like clay for the support it offers their roots, and if you’re looking for crops that grow just about anywhere and can be planted later in the season when clay soils are driest, look no further than pumpkins and squash.
Negatives of Clay Soil
The downsides of clay soil are perhaps better known than the positives. All of these nutrients are useless if they are bound up in compacted clay. Plants (and beneficial microbes) need oxygen in order to access nutrients, and so compacted, dense, clay soils pose major problems for growing plants.
Not only does a lack of aeration it make it hard for roots to break through heavy soils, but it also makes it hard for water to drain. Standing water and run off offer major challenges, and both can result in poor yields.
When to Work Clay Soil
Clay soil requires careful attention when you work it and is perhaps the most finicky soil type to deal with. Work clay when it is too wet and it will compact, reducing aeration and drainage and resulting in very low vegetable yields. Plant when it is too dry and the soil will shatter into dust, which turns into heavy mud and then brick-like clay the minute it gets wet and dries.
There are a few “tricks” gardeners use to tell when clay soil is ready to be worked. Oregon-certified nursery professional, Rod Smith, says “test the soil by squeezing a handful into a lump, then push your thumb into the lump. If it dents like modeling clay, it is too wet. If it crumbles, then it is perfect to work.”
If you live in areas with long, wet springs, waiting for clay to dry out can seem interminable and can pose a real setback for early crops. If you have multiple gardens or fields with different soil types, consider leaving the clay areas for later crops, and start your early crops in loam, gravel, or sandier soils. If clay is all you’ve got, then you’ll need to look into some improvement strategies.
Improving clay soil yields impressive results, but it does take time. There are several approaches you can take to boost the tilth of your beds.
Adding sand, grit, or fine gravel to your soil is one of the simplest ways to improve aeration, but these materials are expensive and impractical on a large scale. However, if you have a small garden, a bulk order of these materials might be your best bet.
Organic material is another option. Rough organic materials like straw, garden compost, chopped leaves, and weathered compost help aerate the soil and build fertility. Over time, organic materials can dramatically improve the productivity of your garden by supplying nutrients.
Compaction is the clay gardener’s biggest enemy. Plants cannot grow well, if at all, in compacted clay soils, which is why it is so important to wait until the soil is dry enough to work. Raised beds can help with clay soils by clearly demarcating pathways and growing spaces so that only the pathways compact.
Of course, protecting the pathways is not a bad idea either, for both your garden’s sake and the sake of your boots. Heavy mulching or even using wooden boards during the wettest parts of the spring and winter will prevent your pathways from compacting too much while also allowing you to access your garden.
Mulching helps with more than just pathway preservation. Heavy rain can compact the surface of your clay soil, reducing drainage and damaging your plants. Mulch protects your soil from impact, boosting soil moisture while also reducing weeds and, in some cases, improving soil tilth and fertility (if you use mulches made from organic materials).
Planting in Clay Soils
Aeration is key to plant growth if you have clay soils. Adding organic materials is a start, but you may also have to aerate the soil by hand. A broadfork makes this easy, and saves your back from dealing with heavy clay. Trust me, the last thing you want to do is turn a bed of clay soil with a bad back.
As you transplant, you can always add soil amendments to the hole. Mixing existing clay soil with compost, sand, and slow releasing fertilizers or amendments like bone meal will improve both aeration and fertility, helping your transplants thrive.
Clay soils are tricky, but once you come to terms with their quirks, your garden is free to bloom. Do you have any tips for gardening in clay soils you would like to share with other Dave’s Garden readers? Please leave a comment!
Vegetables That Grow In Clay Soil
Is it true that there are vegetables that grow in clay soil?
You know clay has its advantages but being good for vegetables is not one of them.
So when I discovered some vegetables actually do well in clay, I felt like shouting “yippee!”
And I swore to share them with you.
So, if you want to know about crops for clay soil, hold on right there.
Why Clay Soil Is Frustrating?
First, I am sure you would like to know what makes clay so stubborn as far as growing greens is concerned.. .
Now, Plants (and useful microbes) will need oxygen so as to access important nutrients.
However, naturally, clay soil is highly compacted, and dense thus it has little aeration.
Thus, growing plants hardly reach the nutrients.
In addition, it drains water poorly and instances of standing water are ever so common in wet weather.
Come to spring and it further irritates crops by taking forever to warm.
The bottom line is that even the most daring crop will find it very hard to survive such tough conditions.
Improving clay soil
you can make clay more vegetable friendly by Improving it.
Here are some approaches I take:
Add grit, sand, or fine gravel
This is an incredibly simple way to breathe life into your stubborn clay. Adding these materials improve aeration.
But there’s a catch:
These components are expensive and largely impractical, especially on large scale. Still, even if you just have a small yard, you need significant quantities of these materials.
Applying Rough organic materials can help aerate it. I am talking about items like straw, chopped leaves, garden compost, and even weathered compost.
These materials also build fertility.
Mulch protects your sticky earth from impact. This improves soil moisture levels while reducing weeds.
If your mulch is sourced from organic materials, you get a bonus of better fertility
All in all, improving clay soil gives wonderful results. The problem is that it takes time.
Okay? Very good!
Now, let’s me introduce your long-awaited crops that thrive well in clay soil (vegetables)
Now, there a couple of things you need to know:
- First, shallow-rooted vegetables tolerate—and even benefit from heavy clays because such clays are highly stable.
- Then, Other root crops, such as daikon radishes plus potatoes, help in breaking up heavy clay soil.
- Lastly, heavy clay soils warm slowly, hence you can forget about planting early spring crops.
Finally, here is my high-value list of the veggies to plant in clay:
Broccoli- like most brassicas- requires heavier soils .
When grown in clay, broccoli doesn’t need heavy watering provided your soils’ moisture content remains at acceptable levels.
These cabbage relatives actually yield firmer heads when planted in clay soil and really thrives in cool weather. Remember to keep an eye on the soils Ph and moisture content.
Cabbage grows well in almost all soils, provided that it’s well drained. Thus, be sure to amend your clay soil with compost before planting.
To add nutrients, you can Apply compost tea or fish emulsion around a month after planting.
Cauliflowers survive in clay also. However, work your soil by adding compost or mature manure before planting.
Kale prefers loamy soil types (sand, silt & clay). Add enough compost plus aged manure in soil preparation.
Bean plants aren’t choosy when picking their growing conditions. They, therefore, thrive in compact clay soil, provided it’s amended with compost.
These plants generally grow well in almost any soil. Avoid over watering them when planted on clay, as flooding water encourages wilting on top of root rot diseases.
Potatoes reduce compaction and prefer gardens heavy in organic matter and with a fairly acid pH
Daikon radish(Forage radish)
This again helps break up your clay soil. It matures without many preparations.
Both winter and summer squashes do well in all clay soils. However, add rotted manure or lots of compost to aide drainage
Pumpkins are not that fussy regarding soil texture. However, they still require fertility. So add one spade of well-rotted manure or compost to every hill during planting.
Bulbs like onions and leeks
These shine in well drained and fertile soil. Raised beds, enhanced with more compost are recommended. You can also apply fish emulsion/compost tea to encourage fast growth.
Swiss chard tolerates enriched and well drained clay soils. You just add a lot of compost when preparing the soil.
Final Round Up
If you were to ask them, Even vegetables that grow in clay soil will tell you that they prefer excellent drainage and top fertility.
Amending your clay soil makes the conditions friendlier to clay-loving vegetables and improves your harvest.
With your soil well worked, you will happily grow and enjoy rich vegetables like broccoli, kale ,Brussels sprouts, cabbages, potato, cauliflower, bean, daikon radish and pea
And those are the vegetables that grow in clay soil.
Starting a vegetable garden in clay soil is possible if you have patience and stick to the rules. Learn about amending and mulching for the best crops.
Many people, who like gardening, feel that with proper care and nourishment, what you grow rewards you with handsome flora, feed, and foliage. But, have you thought about how to amend clay soil for vegetable gardening?
I’m happy to have Ann Sanders as a guest contributor on PreparednessMama:
There might be a lot of questions in your mind, like “How to grow food for yourself if you have nothing but clay soil?” or “Is clay soil nourishing enough for the vegetables to grow?” Well, worry not. You will soon witness the clay mess in your garden turn into black gold! Handling gunky clay is a challenge in home gardening. It is slimy and heavy when wet, and goes hard when dried.
I have been working with clay soil for a long time by converting it into a medium, rich in nutrients. Mixing it with an appropriate organic mix does the deed. This is why, I am providing you with some fantastic tips for starting a vegetable garden in clay soil, like a pro. So, get your gardening tools ready.
Transform Difficult Clay Into Gold
If you are trying to improve the clay soil in your garden and think that it can happen overnight, you need to understand that with soil amending, patience is a virtue. Though it may seem a big task at first, these tips will give impressive results in the end.
There are numerous approaches for boosting the tilth of clay filled beds, let’s look at three of the most common.
Adding amendments to clay soil help to give it structure. Consider fine pea gravel, sand or silt.
Add about 3 inches to the top of the soil and work it into the soil to a depth of about 8 inches. These will help the soil fall apart and works in opposition to the lumpiness, the clay soil imparts. It provides a huge amount of aeration beneath the soil.
Add Organic Compost
Waste and rough organic matter are an easy addition. It includes substances like garden compost, animal waste compost, bone compost, straw, chopped leaves and dried organic matter. They improve the aeration quality further, by pulling the spoil apart.
You want to add some kind of aged compost every time you plant. It helps in improving soil fertility and brings microbes to the soil, thereby increasing the nutrient quantity.
Many types of mulch are readily available and inexpensive. Check with local tree trimmers for softwood shredding. They will often deliver it for free. A layer of thick, soft sawdust can provide a clay bed with an absorptive surface just right for sucking up all the extra water that would log itself in the clay.
How To Grow Vegetables In Your Clay-filled Backyard
Hard clay soil is tough to till and difficult for delicate roots to penetrate. An extreme clay soil tends to become waterlogged and sticky. Here are two of the easiest methods to go around the problem.
#1. Stay Compost Focused
Tilling – Tilling reshuffles the soil and breaks up the hard chunks of clay soil. It is equally important for putting away all the rocks that show up while tilling.
Composting – A lot of compost is a must for any type of gardening soil. The compost needs to be mixed with the soil as deep as 6-8 inches. If the gardening area is big, a tiller works well and can mix the compost with the clay soil, even up to 12 inches deep.
The compost and clay once mixed, will resolve the issue of flooding in the garden on being watered. In other words, the soil becomes more absorptive.
Mixing can be done using a garden tiller, over and over, for at least 4-5 times, till the blades run in, smooth.
Mulching – Wood mulch that can be found at the carpenter’s workshop or even a construction site. Be sure to stay away from pressure treated lumber though; it is not a good addition to your garden because of the chemicals. Be sure to add a thick layer of cardboard to the soil before laying the mulch over the corrected clay.
Planting And Watering – Timely watering is a must, once the beds have been planted.
#2. Remain Mulch Focused
If just a small part of your garden has the clay makeup and it is hard for a shovel to get through it, then a different method can be used.
Digging Deep – For this, a 4-5 feet deep sink hole is dug, at the identified spot. The edges of the hole are lined with a tough gardening fabric, which does not tear apart with the pressure.
Wood Layering – The bottom of this huge bed is filled with wood shavings. This is called as hugelkultur. The bed of wood dust and shreds acts as a sponge and absorbs all the water. This makes a fantastic drainage technique and removes the problem of water logging.
Composting – The next layer can be good soil, containing nitrogen rich manure such as chicken manure. The compost of your liking can be used. Over this, the compost and clay soil mix can go, together with the wood shavings, again. Veggies like tomatoes, zucchini, carrots, radish, corn, green beans, and beets are easy to grow in tempered clay soil.
Starting a vegetable garden in clay soil is possible if you have patience and stick to the rules. Aerate your soil with amendments, utilize compost for additional nutrient value, and remain mulch focused to help remove additional water from the soil.
I hope this article has cleared most of your doubts regarding vegetable gardening in clay soil. Let us know if you have any other clay soil amendments that have worked in your garden. You can leave a comment below. Happy Gardening!
Author Bio: Ann Sanders is a gardener with over 5 years experience. With the endless passion for organic living, she’d like to become an inspirator in this field. Follow her on Facebook and Twitter”
For more soil building information try these titles from Amazon:
Different soils have different textures and properties that should be considered when growing different things in them.
In this short guide, we outline what might grow well in clay soils and heavier types of soil.
Characteristics Of, & Profile Of Clay Soil
Pure clay soil tends to:
- Have the smallest soil particles when compared to silt, and sand
- Hold/retain a lot of moisture and water and have poor drainage (because of how tightly compacted the small clay particles are)
- Be poorly aerated
- Be sticky and clumped together when wet – making it hard for root vegetables to establish roots in the clay, and making it hard for gardeners to work with it
- Crack and go solid when they dry out – which can dislodge certain root systems
- Hold onto nutrients, but can be hard to access for plants and other things growing in clay.
Working With, Improving & Amending Clay Soil
Compost, leaf mould, coarse grit and well-rotted bark chips can work well when added in moderate amounts to clay soil. Liming agents like calcium can also work well in moderate amounts with clay.
However, as mentioned by Empressofdirt.net, sometimes the clay soil in your area might be too extreme for modifications and amending, and raised garden beds with imported soil might work better for growing.
Read these sources for more info on amending, improving and working with clay soil:
A Note On Soil Types, & What Ultimately Impacts How Things Grow
Before we look at what grows well in clay soil, it’s important to note that all soils are slightly different in composition depending on the location (you might get a pure clay soil in one location, but in another you might get a mixed clay soil or a soil with different characteristics), there are different external factors acting upon each soil, and ultimately, there are many physical, chemical and biological factors that determine how well something grows in a particular spot or under particular conditions.
This is just a guide on clay soils in general, without going into extreme depth about all these other factors (factors like soil fertility, soil health, soil quality, fertilizer added, top soil added, pesticides added, tilling practices and so on).
It would do you well in the long term to get information on the soil in your location (what it is and what is the best way to manage it), the climate in your location (temperature, rainfall etc.) and the growing seasons (for example – the US has different planting zones), the plants or things you want to grow and the conditions they need – and come up with a specific plan for your situation.
Plants & Flowers That Grow Well In Clay Soil
- Black Eyed Susan
- Russian Sage
- Little Bluestem
- Purple Coneflower
- Sea Holly
- Perennial Geranium
- False Sunflower
- Blazing Star
- Bee Balm
- Euphorbia characias subsp. wulfenii
- Hydrangea macrophylla
- Lychnis coronaria
- Chinese lantern
Flowering perennials and bulbs:
- Alchemilla mollis
- Japanese anemone.
Fruits & Fruit Trees That Grow Well In Clay Soil
- Citrus trees
- Stone fruits
Vegetables & Crops That Grow Well In Clay Soil
- Lettuce, chard, green beans beans and other crops with shallow roots
- Broccoli, Brussel sprouts and cabbage often grow better in clay soil than looser loams
- Mid and late season sweetcorn are a good choice, too, but some of the best vegetables to grow in clay are squash and pumpkins.
- As long as they are grown in planting holes that have been generously enriched with compost, summer squash and small pumpkins seem to do well no matter where they are grown
- Rice can also work well in clay
- Brussels sprouts
- Cabbage (red and green)
- Cabbage (Napa and savoy)
- Daikon radish
- Bean varieties
- Carrots and beets
- Swiss chard
- Rice varieties
Trees, Shrubs and Bushes That Grow Well In Clay Soil
Trees and shrubs:
- Snowy mespilus
- Crab apple
- Strawberry tree
- Cotoneaster ‘Hybridus Pendulus’
- Chaenomeles (flowering quince)
Plants For Wet Clay Soil
Best Cover Crops For Clay Soil: Fixing Clay Soil With Cover Crops
Think of cover crops as living mulch. The term refers to crops you grow to serve some of the same purposes as mulch: to cover and protect fallow soil from weeds and erosion. Cover crops can be tilled back into the soil to improve its nutrients or organic content. This is useful for fixing clay soil with cover crops. Read on for information about cover crop plants for clay soil.
Using Cover Crops to Improve Clay Soil
Clay soil is problematic for gardeners since it is heavy and doesn’t allow water to drain through easily. Many common garden crops and ornamentals require well-draining soil for best growth.
Clay soil has advantages as well as disadvantages. Unlike sandy soil, it holds whatever water and nutrients come its way, but it is heavily goopy when wet and hard as bricks when dry.
The key to working with clay
soil is to add organic material to it. One way to do this to start using cover crops to improve clay soil.
Cover Crop Plants for Clay Soil
Since organic matter will make your clay soil easier to work and better for your plants, your job is to decide what form of organic matter to use. You can work in 6 inches of raw materials, like chopped leaves or fresh manure, in autumn and allow the soil microbes to break the material into humus your plants need.
Another option, and perhaps an easier one if you have time and patience, is fixing clay soil with cover crops. You’ll have to plan ahead, since you want to plant these in your garden well before you plant your veggies or flowers.
Depending on the cover crop you choose, you can till these under before they go to seed. Their bulk will both loosen the clay soil and add extra nitrogen to boost the garden crops later.
Best Cover Crops for Clay Soil
Some of the best cover crops for clay soil are clover, winter wheat and buckwheat. You can also select crops with deep tap roots, like alfalfa and fava beans, to pull nutrients into the top soil from the subsoil while, at the same time, breaking up the compact clay.
Plant these crops in the fall, after the rains begin, so that the soil is softer. Allow them to grow all winter, then till them into the soil in the spring before they seed.
For maximum organic content, plant a second cover crop in spring to be tilled under in autumn. A full year of cover crops may be what you need to make your garden happy.
Using Cover Crops to Improve Soil and Water Quality
This is a literature review of cover crop benefits from Dabney et al. 2001 and Dabney 1996. Cover crop benefits include: soil erosion protection, reduced nutrient leaching, carbon sequestration, weed suppression and integrated pest management. Cover crops protect water quality by reducing losses of nutrients, pesticides and sediment. Only a small percentage of farmers actually plant cover crops because most farmers believe the disadvantages outweigh the advantages. This fact sheet attempts to highlight the physical, chemical, biological and economic benefits of using cover crops in a sustainable cropping system.
Cover Crops and Water Quality
Sediment is agriculture’s number one pollutant. Water erosion occurs even on flat soils and is especially a problem on hilly soils. Cover crops produce more vegetative biomass than volunteer plants; transpire water, increase water infiltration and decrease surface runoff and runoff velocity. If the velocity of runoff water is doubled in a stream, the carrying capacity of water or the stream competence to transport soil sediment and nutrients increases by a factor of 26. So 64 times more sediment and nutrients are lost with moving water when the velocity is doubled (Walker et al. 2006). Cover crops protect soil aggregates from the impact of raindrops by reducing soil aggregate breakdown. By slowing down wind speeds at ground level and decreasing the velocity of water in runoff, cover crops greatly reduce wind and water erosion.
Cover crops can increase nutrient efficiency through reduced soil erosion (less soil organic matter and soil nutrient losses in the topsoil). Cover crops are scavengers of residual nitrogen (N), converting N to proteins (enzymes, hormones, amino acids). Nitrogen uptake depends on soil N, climate, cover crop species, seeding rate, planting and killing date. Winter grass cover crops (cereal rye, annual ryegrass) accumulate N in the fall and winter due to fast root growth. After the boot stage, there is not much additional N uptake with grasses. Legumes accumulate N longer in the spring but with high soil N, legume N fixation decreases. Use grass or brassica species to absorb and recycle N if excess N occurs from manure or fertilizer. Use legumes to supplement N for the next crop if more N is needed for fertilization.
|Table 1. Advantages and Disadvantages of Using Cover Crops.|
|Reduce soil erosion, increase residue cover||Planted when time and labor is limited|
|Increased water infiltration||Addition costs (planting and killing)|
|Increased soil organic carbon||Reduced or increased soil moisture effects depending on weather or management|
|Improved soil physical properties/reduced soil compaction and improved field trafficability||Difficult to incorporate cover crops with tillage|
|Recycle nutrients, fix nitrogen with legumes||May increase disease risks|
|Improve weed control, beneficial insects, disease suppression||May increase insect pests|
|Wildlife habitat and landscape aesthetics||Allelopathic effects|
Pesticide usage can either increase or decrease with cover crops. If cover crops are difficult to control, pesticide use may increase. In South America, 95 percent of some areas use cover crops with no-till to promote weed suppression through dense plantings and competition with weeds for sunlight, water and nutrients. Cereal rye has been shown to have an allelopathic effect on weeds for up to six weeks. Living mulches are better at suppressing weeds than dead mulches. In soybeans, Pythium disease (damping off) decreases because the delaying planting (five to 14 days) warms the soil. In long-term studies, cover crops reduced the populations of some soil-borne pathogens. Soybean cyst nematodes are significantly reduced by annual ryegrass and cereal rye cover crops. Some green cover crops attract armyworm, cutworms and slugs, so the cover crop needs to be killed three to four weeks before corn planting. Cover crops can be used as a trap crop for corn earworm, tarnish bug and other insects if the cover crop is killed early. Letting cover crops grow and mature may allow populations of beneficial insects to increase. Cover crops complement no-till more than conventionally tilled soils because cover crops may be difficult to incorporate into the soil. There is a need to understand insect cycles and pest interactions with cover crops.
Cover Crops and Soil Quality
Cover crops can greatly increase carbon inputs into the soil. Reduced tillage plus carbon (C) inputs from residues increase soil organic carbon. Both C and N are needed to form soil organic matter. Grass cover crops may contribute N as scavengers or legumes may fix additional N. Grasses contributes more carbon than legumes due to a higher C:N ration. At C:N ratios less than 20, N is released. The average C:N ratio in the soil is around 10-12:1 indicating that N is available. The soil microbial biomass and enzymatic activity increases with cover crop usage. Cover crops increase SOM, macroporosity, soil permeability, mean aggregate size and aggregate stability (macroaggregates vs. microaggregates). Deep rooted cover crops increase subsoil water holding capacity. A bare soil holds 1.7 inches of water while a continuous living cover holds 4.2 inches of soil water (USDA-NRCS Engineering handbook). Increased soil structure and stability may improve the soil’s capacity to carry machines and improve field accessibility, and decrease soil compaction.
The release of N from cover crops for the following crop at the right time is an issue. If nutrients are tied up or immobilized from the soil, crop yields can decrease especially in no-till corn. The release of N depends on cover crop species, growth stage, management and climate. An early spring kill of grasses promotes a lower C:N ratio and a faster release of N. Legumes tend to have a lower C:N ratio but if either grasses or legumes are allowed to reach full maturity, N release is delayed. Slower N release occurs more in dry weather than in wet years due to decreased microbial activity needed to decompose residues, and release N volatilization of cover crops left on the soil surface has been suggested but only small losses of NH3 have been shown to occur with no-till. Leaching (37 percent) of nitrates into the soil had a bigger effect than volatilization (4 to 6 percent) losses. N uptake of cover crops varied from 51 to 270 pounds per acre (57 to 296 kg N/ha) to the next crop. If 50 percent of N is recycled, cover crops may supply 22 to 120 pounds per acre (25 to 132 kg N/ha) to the next crop. Late planted cover crops may not have as much vegetative growth but may impact soil and water quality through reduced soil erosion.
|Carbon to nitrogen (C:N) ratio.||Macroaggregate hierarchy (from Tisdall & Oades, 1982).|
Cover crops increase mycorrhizal fungus activity promoting a symbiotic relationship with the plants’ roots for water and nutrient uptake. Plants provide the polysaccharides and the mycorrhizal fungus provide the protein to form a glycoprotein called glomalin which promotes soil aggregate stability (more macroaggregates) and improved soil structure. Mycorrhizal fungus grows better in undisturbed soils. No-till and actively growing roots promote this reaction to occur. The majority of soil microbes are located next to growing roots with 10,000 times more microbes located in the rhizosphere next to the root than in bare soil.
|Mycorrhizal fungus and plant roots. (Photo from Building Soils for Better Crops 2nd Ed. by Fred Magdoff and Harold van Es)||Glomalin surrounding soil particles. (Photo from Dr. Sara Wright, USDA-ARS)|
Cover crops may benefit or hurt crop yields due to changes in soil moisture. While cover crops increase water infiltration, they also transpire soil water and dry out fields, possibly affecting yields. In Ohio, fields are wet seven out of 10 years in the spring, so transpiration from living covers may be beneficial to dry out the soil. However, if a cover crop is killed late after considerable cover crop growth and then it turns wet, the cover crop may trap soil moisture and delay planting. If an early spring drought occurs, cover crops may hurt crop yields from reduced soil moisture. However, deep rooted cover crops improve corn rooting depth to attain subsoil moisture and moisture is conserved by mulching the topsoil in a dry year. A pound of soil organic matter has the ability to absorb 18 to 20 pounds of water, which is beneficial in a dry year. Some of the negative soil moisture effects from using cover crops can be negated as soil compaction decreases and soil quality improves with time. Cover crops may be utilized to improve soil physical, chemical and biological properties that improve soil drainage but it takes time to make these changes if soil compaction is high and soil quality is low.
Living cover crops can significantly alter soil temperatures. Cover crops decrease the amplitude of day and night temperatures more than average temperatures resulting in less variability. Cover crop mulches protect the soil from cold nights and slow cooling. This may be a benefit in hot regions, but may slow growth in cooler regions. Winter cover crops moderate temperatures in the winter. Standing crops have higher soil temperatures than flat crops. Row cleaners can be used to manage residues to improve soil temperatures in no-till fields. Temperature and rain fall are the primary climatic variables affecting cover crop selection and establishment. Broadcasting cover crop seed is faster and cheaper but stand establishment depends on rainfall and good seed to soil contact. Most winter cover crops need to be planted in late summer or early fall (by September) to survive the winter (except cereal rye which can be planted later).
|Soil erosion, sediment and nutrient losses from cropland. (NRCS photo)||Soybeans no-tilled into a cover crop. (Photo from Dr. J. Morales Sa)|
Summary of Cover Crop Effects on Soil and Water
- Cover crops are grown when the soil is fallow.
- Increase the solar energy harvest and increase carbon in the soil.
- Provide food for macro- and micro-organisms and other wildlife.
- Increase evapotranspiration, increase water infiltration and decrease soil bulk density.
- Reduce sediment production, decrease impacts of raindrops and decrease runoff velocity.
- Increase soil quality by improving the biological, chemical and physical soil properties.
- Increase organic carbon, cation exchange capacity, aggregate stability and water infiltration.
- Grass and brassica species are great N scavengers and increase carbon inputs.
- Legumes increase soil N through nitrogen fixation.
- Cover crops grow best in warm moist areas but may hurt yields in semi-arid regions.
- Soil temperatures may impact yields.
- Systems are needed that reduce the cost of cover crop establishment and killing.
- Cover crops improve soil and water quality. May reduce nutrient and pesticide runoff by 50 percent or more, decrease soil erosion by 90 percent, reduce sediment loading by 75 percent and reduce pathogen loading by 60 percent.
This fact sheet was produced in conjunction with the Midwest Cover Crops Council (MCCC). Outside reviewer: Mark Fritz, Ohio Department of Agriculture.
Cover Crops – Protect and Improve Your Soil
Back to Succession Planting
Back to Caring for Your Garden
Farmers around the world grow cover crops to increase crop yields. Cover crops, also known as green manures, are an excellent tool for vegetable gardeners, especially where manures and compost are unavailable. They lessen soil erosion during the winter, add organic material when turned under in the spring, improve soil quality, and add valuable nutrients.
Popular fall-planted cover crops include oats, winter rye, winter wheat, crimson clover and hairy vetch (see the chart at the end of this fact sheet). The latter two crops are legumes- plants that can add a lot of nitrogen to your soil after they decompose. These crops are typically planted as early as August 15, but no later than October 10. They should make some growth before the first hard frost. Some cover crops (oats and daikon radish) are killed by cold winter temperature, but most go dormant and resume growth in the spring. Cover crop roots grow deeply into the soil pulling up nutrients that might otherwise leach out of the soil. The crops are turned into the soil before going to seed, usually sometime in late April or early May. Other cover crops, like buckwheat and Dutch white clover, are sown in the spring or summer to cover and improve bare soil.
These are some suggested steps for experimenting with cover crops this fall:
- Decide which cover crops to plant. Combine legumes and non-legumes when possible. Sow oats if this is your first time trying a cover crop or if you want to be able to plant early spring vegetables. Oats are killed by the first hard freeze, leaving a brown decomposing mat in spring.
- Purchase seed locally if possible from a farm supply store or garden center. You can also order cover crop seeds from most retail seed companies. (See the end of HG# 70 “Recommended Vegetable Cultivars for Maryland”.)
- To sow a cover crop over an entire bed: Prepare the soil by tilling under or removing plant wastes and mulch from the summer. Then rake the area smooth.
- To sow a cover crop while vegetable crops are still producing: Remove mulch from around plants and rake the area smooth. Your cover crop will get a good start but will not interfere with vegetable plant growth.
- Now let’s plant: The seed must directly contact soil to germinate. Use the amount of seed shown in the chart. Broadcast the seed by hand or with a hand-held broadcast seeder, preferably before a rain, and gently rake seeds evenly into the soil. Then walk on the seeds to press them into the soil. Mixing seeds with soil or compost will make it easier to distribute the cover crop seeds evenly by hand.
- Winter wheat and winter rye will produce massive root systems- great for breaking up tight, clay soil. They are also difficult to turn under in the spring unless you have access to a tiller.
- Remember that spring planting may be delayed somewhat by a cover crop (except for oats and daikon radish), since you must allow about 2 weeks for the plants to break down.
Be a good steward of the earth by planting a cover crop this fall.
A mixture of winter wheat (tall plants) with hairy vetch (vining plants).
Oats planted in the fall beginning to die from cold winter temperatures.
Fast growing daikon or forage radish sown in the fall produces a large root that can help break up compacted soil.
Crimson clover holding soil in place on the sloped end of a raised bed.
Large tillers are useful for turning under winter cover crop in the spring.
Buckwheat blooms attract bees.
Crimson clover in bloom.
*Will winter-kill in most years, leaving a “mat” of dead vegetation which can be planted through in spring or turned under.
**Sow late summer/fall crops from August 15- October 1, depending on location, species, and weather forecast.
*** Legumes, like crimson clover and hairy vetch take nitrogen from air and convert it into a form used by the plants. You can aid this natural process by purchasing an innoculant with your seed – Rhizobia spp. bacteria. You coat the cover crop seeds with the innoclant by mixing them together in a bag.
Maryland Grows Blog Posts on Cover Crops
Back to top
Reviewer: Raymond Weil, Ph.D., Dept. of Environmental Science and Technology, University of Maryland.
Author: Jon Traunfeld, University of Maryland Extension, Home and Garden Information Center
Use Cover Crops to Improve Soil
For Related Articles and More Information, Please Visit OCA’s Farm Issues Page, and our Organic Transitions Page.
There are three main ways to improve soil: grow cover crops, mulch the surface with biodegradable mulches, and/or dig in organic soil amendments (such as compost, grass clippings, rotted manure or wood chips). All have their advantages and none should be discounted, but cover cropping is the method least likely to be practiced in home gardens. There is a reason for this: Information on using cover crops is tailored to the needs of farmers who use tractors to make short work of mowing down or turning under cover crops. But when your main tools for taking down plants have wooden handles and you measure your space in feet rather than acres, you need a special set of cover crop plants, and special methods for using them.
How Cover Crops Help
A cover crop is any plant grown for the primary purpose of improving the soil. Since the early 1900s, farmers have used cover crops to restore fertility to worn-out land. In addition to helping bulk up soil with organic matter, cover crops prevent erosion, suppress weeds, and create and cycle soilborne nutrients using the power of the sun. Recent advances in soil biology have revealed two more ways cover crops can improve soil.
Rhizodeposition is a special advantage to working with cover crops. Many plants actually release sugars and other substances through their roots. They are like little solar engines, pumping energy down into the soil. With vigorous cover crop plants, this process goes on much more deeply than you would ever dig — 6 feet for oats and rye! If you are leaving your garden beds bare in winter, you are missing the chance to use cold-hardy crops such as cereal rye or oats to solar-charge your soil. Thanks to this release of sugars, the root tips of many plants host colonies of helpful microorganisms, and as the roots move deeper, the microbes follow.
But so much for scientific talk. If you’ve experimented with cover crops, perhaps you have dug up young fava beans or alfalfa seedlings to marvel at the nitrogen nodules on their roots, or watched a stand of buckwheat go from seed to bloom in four weeks flat. Or how about this one: It’s April and the soil is warming up and drying out. After loosening a clump of fall-sown wheat with a digging fork, you pull up a marvelous mop of fibrous roots and shake out the soil. What crumb! The soil’s structure is nothing short of amazing! These are the moments an organic gardener lives for.
Bio-drilling is what happens when you use a cover crop’s natural talents to “drill” into compacted subsoil. For example, you might grow oilseed or daikon radishes as a cover crop where their spear-shaped roots will stab deep into tight subsoil. Bio-drilling action also takes place when deeply rooted cover crop plants penetrate subsoil and die. Then, the next crop grown may actually follow the rooting network mapped out by the cover crop. Maryland researchers were able to track this process using special camera equipment (a minirhizotron), which took pictures of the interactions between cover crop (canola) and crop plant (soybean) roots. As the canola’s deep roots decomposed, soybean roots followed the trails they blazed in the subsoil, hand in glove. In addition to reduced physical resistance, the soybean roots probably enjoyed better nutrition and the good company of legions of soil-dwelling microcritters, compliments of the cover crop.
As most readers of this site will recognise, nature always works to protect the soil from from wind and water erosion — by covering it with living foliage. In doing so, the cycle of life and death continues, increasing the soil’s fertility over time. Alas, many ‘modern’ gardeners have allowed themselves to become indoctrinated into trying to maintain a ‘tidy’, foliage-free garden bed — they will not rest until they’ve removed every green plant other than their own fruit and veg — but this simply begins a never-ending battle with ‘weeds’, that takes a lot of unnecessary effort, and ensures the soil and soil-life steadily gets depleted of that all-important organic matter and humus content. For many people, this impossible battle ends with chemical warfare…. Striving for a conventional ‘aesthetic’, they are, quite literally, losing the plot.
In its bid to cover up your soil, nature will use whatever resources it has at hand to do so — filling empty spaces from roots and seeds presently found in your soil. Some of these hardy pioneers, however, have characteristics that aren’t the most congenial to your particular purposes. Some are invasive, choking out the plants you really want, and some are just plain prickly! Over time, these plants normally bring a lot of benefit, but if we put a little design into this aspect, we can help ensure the empty spaces in our gardens and farms accommodate just the plants we want — those that serve multiple functions, and which are easier to manage and which work to the benefit of our edibles, rather than out-competing them. By choosing the right combinations, we can have the best of both worlds — a well-covered (protected) soil, plus aspects such as nitrogen fixation, soil aeration, mineral accumulation, large increases in biomass for increased humus accumulation, and more — as well as providing for a beautiful aesthetic!
A cover crop mix of cow pea, vetch, wheat and oats, under a fruiting apple tree
Photo © Craig Mackintosh
One of our forum members shared the chart at top, courtesy of groworganic.com, which I thought well worth putting here on our main page. Cover crops (otherwise known as ‘green manures’), are an important facet of any garden, market garden, or farming system. Getting to know the characteristics of the cover crops suitable for your area is time well spent.
The key ‘features’ you will want to look for when choosing a cover crop mix will somewhat depend on the type of soil you have, and, of course, its level of fertility. For example, if you have a heavy (high in clay content) soil, there is a high risk of compaction, which can create a waterlogged and anaerobic state that will stunt your plants and make them susceptible to disease. Whether you break up the soil with double-digging or not, such soils would benefit from a cover crop with strong and deep root systems that can try to penetrate any hard pans below the soil surface. A soil composition that’s high in sand would benefit from a cover crop mix that provides copious amounts of biomass, helping to increase the organic matter content that will help hold moisture in a way that sandy soils cannot. If your soil is generally depleted, you’ll want to major in nitrogen-fixing plants (most of the legumes fit into this category — like peas, beans, lentils, clovers, etc.), as well as those high in carbon (like rye, oats, wheat, barley, and so on). As you can see, many cover crops can be edible too!
Other benefits of having a diverse mix of cover crops, beyond soil composition and structure, are in providing habitat for beneficial, predatory insects and providing a greater diversity of flowers that improve the health of your local pollinator populations, and also serve as great pest distractors (although often you may want to cut the cover crop just above the soil surface just after flowering, to ensure the plants do not re-seed, if that is something you wish to avoid — but do leave the root systems in the ground where possible, as they will become soil food and ultimately leave aeration channels, and happier micro-organisms, behind!)
If you’re at a loss in which plants to use for your particular soil and circumstances, you might want to take one of our upcoming Sustainable Soils Management Courses with Paul Taylor. Getting to grips with how your soil and soil life functions enables you to be more creative and successful in implementing strategies that work towards abundance (see our course listings for next dates).
Anyway, check out the chart, and do let us know about your own cover crop resources and/or adventures — either by way of comment below, or as a separate article you can send through to me for publishing: editor (at) permaculturenews.org
Cover crop for Clay soil?
Thank you for your question.
Cover crops usually are grown to prevent soil loss from wind and water erosion. Use fast-growing cover crops, such as winter wheat or annual rye, on fall-spaded gardens. A second, and probably more important reason home gardeners should use cover crops is to improve soil structure and increase organic matter. This is accomplished by tilling cover crops into the garden while they’re green and growing. This technique, which is referred to as green manuring, speeds up the natural soil-building process and can reduce weeds. It also improves conditions for beneficial soil microorganisms and earthworms, and increases the soil’s ability to hold water.
Common cover crops include annual ryegrass, Sudan grass, oats, buckwheat and legumes, such as peas, beans, alfalfa, clover and vetch. Leguminous plants are able to host bacteria that take nitrogen from the air and fix it in nodules on root hairs. To assure that the right bacteria are in the soil, inoculate legume seed during planting. Garden centers and nurseries carry the products you’ll need to do this.
You can sow cover crop seeds in the fall and turn them under in the spring. You also can plant them in different sections of the home garden early in the spring. This can be done over several growing seasons. This rotation will improve a large vegetable garden over several years. For example, a home gardener with limited space can select out a section and produce food, and at the same time improve the soil. First, plant peas, and harvest them as early as possible, then turn under the vines. Next, plant snap beans or another legume, harvest and till under again. Finally, plant annual ryegrass as early in the fall as possible. It may die over the winter, but it can be tilled under in time for the new growing season.
Fill bare spots in your garden with a cover crop, but be sure to turn under the cover crop before it goes to seed. Like all plants, cover crops become weeds when they grow where they’re not wanted.
Garden Cover Crops
Seeds are sown into vegetable garden soil—typically in the fall—to preserve and enhance the soil over the winter. They provide a host of benefits:
Prevent soil erosion and compete with weeds in winter when the soil is not being cultivated.
Improve soil porosity and tilth (the physical condition of the soil)
Add large amounts of organic matter to the soil when the lush growth of green, immature crop is tilled under in early spring. Nutrients (nitrogen, phosphorous, potassium, calcium, etc.) are returned to the soil. Cover crops planted primarily for nutrients are known as “green manures.”
Legumes are host to nitrogen-fixation bacteria which extract nitrogen from the air and store it. When turned under, the nitrogen is returned to the soil.
After produce is harvested, till the plant residue into the soil where it will decompose to produce more humus. This prepares the soil for the seed. Use a drop spreader, a broadcast spreader or broadcast seed by hand. For better coverage, make two seeding passes over the garden at right angles to each other. Lightly rake the seed into the top 1/4 inch of soil. The seed must be covered and be in firm contact with the soil for best germination.
Nitrogen fixers. Legumes benefit from use of a seed inoculant when planting.
Large-seeded legume, very good for building tilth and adding organic matter to the soil. Perfect if you’re getting a late start planting your cover crop and/or planning to wait until late spring to plant your garden. Peas like well drained and fertile loam soils.
Planting time: late Sept. to mid Nov. Recommended Seeding Rate: 1 lb. per 200 sq. ft.
Crimson Clover (An Annual Clover)
Colorful and versatile, crimson clover grows readily on both sandy and clay type soils (best with good drainage) and can be used as either a summer or winter cover crop. The dense mass of hairy stems and leaves is very effective against weeds, and will return a large amount of organic matter and nutrients to the soil.
Planting time: late Sept. to mid Oct. Recommended Seeding Rate: 1 lb. per 1000 sq. ft.
Faba Beans (aka Fava Beans)
Earliest of the green manures to mature, allowing you to till them under in mid to late April and get a head start for spring. Its deep taproots help break up clay or compacted soil as well as add nitrogen and humus. Some may experience an allergic reaction to pollen from faba bean blooms.
Planting time: late Sept. to mid Nov. Recommended Seeding Rate: 1 lb. per 100 sq. ft.
Less winter-hardy than hairy vetch, common vetch is best adapted to well-drained, fertile soils. It is not tolerant of wet soils. It is often seeded with a small grain, such as rye. Vetches are annual, vine-type legumes with leaves ending in tendrils.
Recommended Seeding Rate: 1 pound per 400 square feet
Add minimal nitrogen, but are the best tilth builders and quick erosion control.
The perfect tilth builder. And perhaps the most popular cover crop for erosion control because it germinates quickly and grows rapidly in cool weather. Also very hardy.
Planting time: August to early Nov. Recommended Seeding Rate: 1 lb. per 250 sq. ft.
Another great tilth builder and the best summer cover crop.
Planting time: March to July. Recommended Seeding Rate: 1 lb. per 1000 sq. ft.
Gardenway Cover Crop Blend
The most complete Northwest cover crop blend! This mix combines the great growing characteristics of all the major green manure crops suitable for our climate and soils west of the Cascades. Ingredients: 30% Cereal Rye, 27% Austrian Peas, 29% Triticale, 5% Common Vetch, 5% Annual Rye Grass, 2% Crimson Clover.
Planting time: mid Sept. to late Oct. Recommended seeding rate: 1 lb. per 500 sq. ft.