The Ultimate Guide to COVER CROPS


What is a cover crop?

Cover crops are fast-growing plants that are grown to cover bare earth. They are not intended to be harvested and are grown for the improvement of soil quality. They have properties to help you build soil structure. Improving soil quality, water retention and nutrient density for the food you grow. They can save you money on fertilizer. And save you time on weeding as these crops will smoother all weeds preventing their growth. They will also help manage pests in the garden.

But before we go into all that, I think it’s important to understand what types of cover crops there are. The list below are all the plants that are suitable to use as cover crops. We will cover each of them in detail as we continue through this post.

List of Cover Crops

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What Benefits will cover crops give me?

Cover crops can provide lots of benefits to the home gardener as well as those with acres of land. Long gone are the days where these crops are only available to farmers. People are starting to realise how important soil fertility is and are looking to build on this. The list below is not exhaustive but will give you the most common benefits of using green manures.

Benefits of Using Cover Crops.

  • Improve Soil Structure
  • Prevent Erosion of the soil
  • Add Organic Matter to the soil
  • Retains water in the soil
  • Helps to prevent weeds
  • Adds and protects nutrients in the ground
  • Reduces effort needed in preparation
  • Increases biodiversity
  • Controls pests
  • Enhances Mycorrhizal fungi numbers
  • Suppresses nematodes
  • Attracts Beneficial insects
Improving Soil Quality Using Cover Crops (Green Manure)

Green manure is such a good cover crop. There are many varieties of green manure and they all have their own set of properties. These are fast-growing crops that are designed to suppress weeds, and add organic matter to the soil. In this video, I explain how to use green manure cover crops at home in your garden.

Improve Soil Structure

Soil quality is of paramount importance when growing your own food. I am a firm believer in feeding the soil and not your plants.  By looking after the life in your soil they will provide everything your plants require. Using different sorts of green manures as part of your soil building strategy. You can control exactly what nutrients are added to your soils.

Adding any of the above green manures as a cover crop you also build soil structure. This brings in loads of different soil life. Such as earthworms and microbes that help to break down organic matter. Turning this into nutrients that are readily available for your plants.

Prevent Soil Erosion.

Certain types of green manures can be used to prevent soil erosion. Plants like Ryegrass have massive root systems which can act as a net under the ground and stop the weather from washing and blowing away the surface of the soil.

When considering soil erosion recent estimates state that approximately 24 billion tonnes of soil are lost every year to erosion. That is equivalent to 3.4 tonnes for each and every person on the planet. By using green manures, you can prevent this erosion happening to the topsoil surface in your garden.

Adding Organic Matter to Soil

When you look at soil, most people just see dirt. But this dirt is made up of soil, clay, sand, grit and organic matters along with trace minerals. I recently made a live video on this subject on my YouTube channel. These organic matters are the reservoir of the soil. They hold onto water and nutrients and lock them in and release them over time.

Organic matters are what organisms and soil life use to feed on. This creates a whole biodiversity of soil life. Think of it as a whole new world full of creatures whose job it is to bring in nutrients to the soil. This life is what makes your soil so good.

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Retaining Water in Soil with Cover Crops

Cover crops can really help in water retention in soils. They shade the soil from the sun in the first instance which reduces evaporation. Later after being chopped down they absorb water and hold it like a sponge.

The good thing about the organic matter in the soil is that it is only released as the soil dries out. It wicks from within the organic matter and out into the soils. This also not only helps to keep your plants watered but also keeps the soil life alive.

Weed Suppression

Cover crops are fast-growing and more often or not out-compete most weeds. They grow thick too which blocks out the light from any germinating weed seeds. They are fantastic crops to grow to save time and protect the soil over the winter months.

Adding nutrients to the ground

Green manures have various properties and some of these include being called accumulators. The legumes cover crops all will pull nitrogen from the air around them and store it on their roots. They do this by allowing the roots to swell and accumulates Nitrogen in these swellings.

Fall sowed green manures have the added bonus that they also mop up nutrients from the soil. As they grow, they draw up the nutrients left behind from previous crops. You may think this is bad for the ground, but it is actually very good.

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The nutrients are not gone but are just stored and this protects them from being leached away by the winter weather. Without cover crops, the weather would pull the nutrients out of the ground losing them forever. When growing green manures, you save the nutrients and they are recovered when the manure is dug into the ground later in spring.

Reduce soil preparation efforts

Usually at the end of summer after the harvests. There are huge amounts of bare soil in the garden. If this soil is not protected weeds will grow. These weeds are able to take hold over winter months when most gardeners are not paying so much attention to their gardens.

Cover crops reduce the preparation in spring as they stop these weeds from growing and they are much easier to deal with. Simply strim and leave as a mulch or dig in and you’re ready to plant. It’s so much quicker to get ready at planting time.

If you are a new gardener I wrote a blog called 60 Top Gardening Tips For New Gardeners. This will help you prepare the garden.

Increases Biodiversity

Biological diversity is the foundation for your garden soil. Breakdown of the soil life can result in dead soils that will not provide the nutrients required to produce nutrient-dense foods. It has been shown that without cover crops the soil biodiversity numbers are drastically reduced

Furthermore, adding cover crops can increase nematodes and macroinvertebrates which sustain the entire ecosystem. These provide food for microbes further up the food chain continuing the cycle. As these nematodes and macroinvertebrates are consumed, they are passed as faecal matter. This enriches your soils with NPK and other trace minerals and macronutrients.

Controlling Pests.

Some cover crops or green manures are known as Biofumigants. What is a biofumigant? Well basically put, biofumigants are cover crops that are cut and incorporated into the soil. They are a way to manage pests and disease within the soil that can affect your crops.

They Belong to the Brassicaceae family and one of the most popular is Mustards. Containing glucosinolates they can be deadly to many soil-borne nematodes, pathogens and weeds.   These are not frosted hardy plants. Due to their fast growth, they are ideal to sow as a cash crop. Are ideally suited to be used in bare soils when lying dormant. Using this time when soils are vacant you can grow mustard as a biofumigant.

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Basil a reader of the blog.  Has suggested there was recently an article that stated you shouldn’t sow brassicas directly after digging in mustard. The reason for this he says is by doing this there is a possibility to introduce clubroot to your soil. I have been unable to find this article, nor have I ever experienced this.

However, as mustards are brassicas themselves. It could be that the seed contained clubroot and was contaminated.  If this is the case, the suppliers and growers of the seed would have known they had clubroot in their soils. In my opinion, that’s not very ethical.

It is possible that the mustard wasn’t cut down long enough before the brassicas were sown. Therefore, were still decomposing, without finding the article I am unable to understand the whole reasoning behind it.

I thought I would just add this here to allow you to make your own minds up. My suggestion would be to allow it to fully decompose before planting. As I have stated though I have never witnessed this

Enhances Mycorrhizal fungi numbers

Mycorrhizal fungi can be found in most soil types and work synergistically with the plants in the ground. It attaches itself to the root systems on plants and spreads itself out further than the plant’s roots can usually reach by themselves. This can greatly increase the size of the root mass.

Mycorrhizal fungi do not harm the plants but work alongside them providing nutrients and minerals from untapped areas of the soil. They then trade these nutrients with the plants. The fungi are a living organism and the plant’s trade-off carbon and sugars the fungi needs. The fungi in return provide the nutrients the plant needs.

Cover crops greatly increase the ability to protect the soil, so that the natural Mycorrhizal fungi can not only colonize but spread. There could be 15 different species all attached to one tree and over 8,000 in a wooded area. If you could use an x-ray machine you would see a massive root structure underground of very fine filament roots.

Suppresses Nematodes

Before I talk about this, it is important to understand, like everything in life there are good and bad nematodes. Cover crops can really help to suppress the plant-parasitic nematode population. By leaving soils to become fallow instead of growing and incorporating a biofumigant green manure, these nematodes are free to multiply. By using green manures you can greatly reduce them. Mustards are here to the rescue once again.

We have already spoken about biofumigants above, this is another benefit of using cash crops like Mustards. You can ensure your ground is constantly covered providing protection and a constant supply of moisture and food for beneficial microbes that will keep these nematodes under control. When frosts are due, moving to a winter hardy plant like field beans or hairy vetch will allow you to increase nitrogen in your soils over winter.

Attracts Beneficial Insects.

Cash crops like clover and mustard, that are quick to grow. They provide insects with a food and pollen source when it could otherwise be scarce. They are quick to flower. And the flowers are bright to attract the attention of pollinating insects such as bees.

The overwintering crops such as field beans and hairy vetch and many others will flower early in spring and will provide the first flowers of the year. This again is very important for pollinating insects. It has the added bonus of helping with pollination of crops you grow like tomatoes.

When to sow cover crops

There are two types of cover crop and their sowing times vary depending on the results you want. In order to understand when these crops should be sown. We need to put each cover crop into one of two groups. Frost hardy and Non-frost hardy

Frost Hardy Cover Crops

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Non-Frost Hardy Cover Crops

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How to choose a cover crop

We now have our cover crops sectioned off into frost hardy and non-frost hardy, and we also know the times of sowing. This makes life easier in breaking down which one we wish to use. We can further break these groups down into whether we want to use the crop for the following reasons.

  1. Biofumigants
  2. Nitrogen fixers
  3. Organic bulkers
  4. Nutrient grabbers
  5. Cash croppers

The following table will show you each of these groups and what plants are suitable for your desired results. It’s a simple matter of then looking when to sow.

Biofumigants

  • Turnip
  • Fodder Raddish
  • Yellow Mustard
  • Black Mustard
  • Broccoli
  • Sprouts
  • Cabbage
  • Kale
  • Cauliflower

Nitrogen fixers

  • White Clover
  • Sweet Clover
  • Crimson Clover
  • Red Clover
  • Persian Clover
  • Field Beans
  • Broad Beans
  • Fava Beans
  • Hairy Vetch
  • Bingo Red Vetch
  • Spring vetch
  • Solvena Winter Vetch
  • Field Peas
  • Alfalfa
  • Lupins
  • Cow Pea
  • Fenugreek
  • Snap Pea
  • Snow Pea
  • Soybean
  • Sweet Pea
  • Lentils

Organic Bulkers

  • Oil Seed Rape
  • Annual Rye Grass
  • Cereal Rye Grass
  • Sorghum
  • Oats
  • Lentils
  • Fenugreek
  • Hairy Vetch
  • Bingo Red Vetch
  • Spring Vetch
  • Solvena Winter Vetch
  • Alfalfa
  • Wheat
  • Barley
  • Fodder Raddish
  • Turnips
  • Red Clover

Nutrient Grabbers

  • White Clover
  • Sweet Clover
  • Crimson Clover
  • Red Clover
  • Persian Clover
  • Field Beans
  • Broad Beans
  • Fava Beans
  • Hairy Vetch
  • Bingo Red Vetch
  • Sweet Pea
  • Spring Vetch
  • Solvena Winter Vetch
  • Field Peas
  • Alfalfa
  • Lupins
  • Cow Pea
  • Fenugreek
  • Snap Pea
  • Snow Pea
  • Soybean
  • Lentils

Cash Croppers

  • White Clover
  • Sweet Clover
  • Red Clover
  • Persian Clover
  • Fodder Raddish
  • Turnips
  • Yellow Mustard
  • Black Mustard

With the information above you should be ideally set to be able to select what cover crop you need to get the desired results you want in your garden. You have learned on when to sow it also.

How much do cover crops costs?

So, what about costs? Although I can give you a rough guide here, you will need to find out local prices. The figures below for each of the crops are rough estimates in British pounds and the USA and Australian dollars. All Prices are per Kilo and of course, are subject to change. But these figures will give you an idea of what you will roughly be paying.

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Price-Table-2

Please note that the above prices will be subject to change and were correct at the time of writing. Also, note that it will be dependent on your seed company and the time of year you are purchasing seed.

Cover crop seed mixes

Over recent years many people have asked me what the best is to grow with cover crops. A monoculture or a seed mix. There is no right answer to this question. Preferably a mix would be an ideal situation. The great thing about cover crops is you can tailor the mix to suit what you require in the ground.

Growing a single crop can also help you to sort out a particular issue in your soil so one year you may wish to just grow something like hairy vetch or alfalfa to pull in nitrogen and add organic matter. Or you may just need a biofumigant to knock back the nematodes in the soil.

The more diversity you add to your soil the better, so adding a mix is the best way to do this. Choosing complimentary seed that will not out-compete each other will give you the results required.

How to seed cover crops

The seed size will dictate on how to sow your green manure. Larger seed will be sown in rows usually twice the depth of the seed. Smaller seed the size of brassica seed can be broadcast sown and raked into the soil for a better contact.

It is important to irrigate your seed if there is no rain forecast. Seed should take between 5-21 days to germinate. Depending on when sown, will control their initial growth. Some may leap forward while fall sown may start than sit dormant through winter. These are still growing roots, but in spring you will get a growth spurt.

How long do cover crops take to grow

Depending on the variety you choose cover crops can take anything from 4 weeks to 12 weeks to grow. However, fall sown crops will grow very slowly over winter. Then jump into action in the spring. Radish, clover and mustards will be the quickest to germinate and grow.

When to cut your cover crop?

Green manure cover crops will need to be dug in around 4 weeks before the ground is required. This will give them time to start breaking down. If you are using No-Till methods chop down around 6 weeks before the ground is needed. Clovers and mustards are best to be dug in at flower time to prevent them from going to seed as this is an extremely quick process.

Does cover crops attract slugs?

I have been asked on several occasions about cover crops and slugs. The question was. Do you get more slugs when you grow cover crops? The short answer is no, you do not get more slugs by growing green manures as cover crops. Even if you chop and drop the crop, it doesn’t increase the slug population.

This was tested in Oxford and Hampshire in the UK. Where several plots of land were planted with cover crops over a few years. Slugs were harvested and counted and found that numbers did not increase due to the use of cover crops. If you want to know how to tackle slugs in the garden, check out this blog. Or this video.

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Can you use cover crops in raised beds and containers?

Both containers and raised beds can benefit from cover crops. They will help to not only build the layers of the soil within the unit. But will also help deal with the build-up of pests. Containers and beds can get all the same benefits we have discussed in a small space.

Consider using smaller crops like mustards, and clovers and this will be perfect for containers. For beds, you can use everything we have previously discussed.

The cons of cover crops

One of the cons of cover crops is their price, this is added expense to the gardener. However, I believe the pros outweigh this cost. Another would be the time tilling in the cover crop. Again, we have discussed where we saved time by not having to weed.

There are reports of cover crops reducing or increasing the moisture effects of the soil based on local weather conditions. There are also times that a cover crop can increase pests and diseases and this maybe one of the reasons. Where Basil, a reader, states he had clubroot after sowing brassicas after mustards.

Allelopathic issues may also be caused due to the effects of the biochemicals released during the tilling in process. This can sometimes affect specific follow on crops. You should research which cover crop and the effects it will provide for each area of the garden. You need your rotation plan in place to understand what crops will follow,

Are Cover Crops Worth It?

Of course, they are worth it. Cover crops have so many benefits, they are relatively cheap. They improve soil structure and soil quality. Increases nitrogen and other nutrients. Adds organic matter to the soil and aids in water retention. They can protect soils over winter and even keep building the soil life.

Cover crops are something that every gardener should use to help improve and protect their soils. This will be a great addition to helping any garden build their soil quality.

I hope you enjoyed this blog and got something from it. If you did please help by sharing it with friends and on social media. If you’re interested in building soil quality may I suggest you read my complete guide on composting.

Tony 

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