Learn More About Green Manure Cover Crops
By: Nikki Tilley, Author of The Bulb-o-licious Garden
The use of green manure cover crops is a popular practice among many growers in the farming and agricultural industries. This method of organic fertilizing has numerous benefits for the home gardener as well.
What is Green Manure?
Green manure is a term used to describe specific plant or crop varieties that are grown and turned into the soil to improve its overall quality. A green manure crop can be cut and then plowed into the soil or simply left in the ground for an extended period prior to tilling garden areas. Examples of green manure crops include grass mixtures and legume plants. Some of the most commonly used are:
- Annual ryegrass
- Winter wheat
Green Manure Crop Benefits
The growing and turning of green manure cover crops provides additional nutrients and organic matter to the soil. When incorporated into the soil, these plants break down, eventually releasing important nutrients, such as nitrogen, that are necessary for adequate plant growth. It also increases soil drainage and water retention capabilities.
In addition to adding nutrients and organic materials to the soil, green manure crops can be grown to scavenge leftover nutrients following the harvest season. This helps prevent leaching, soil erosion, and weed growth.
Making Green Manure
When making green manure cover crops, consider the season, the site, and the specific needs of the soil. For instance, a good green manure crop for fall or winter would be a cool-season grass like winter rye. Heat-loving crops, like beans, are good for spring and summer. For garden areas in need of additional nitrogen, legumes, such as clover, are ideal.
Green manure crops should be turned just before flowering. However, it is also acceptable to wait until the crop has died off. Since green manure crops grow quickly, they make an ideal choice for amending soil prior to spring planting.
Learning more about green manure crops can provide home gardeners with the tools necessary for acquiring the optimal soil quality. The healthier the soil, the greater gardening success.
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Read more about Cover Crops
How To Plant A Green Manure Crop This Spring To Recharge Your Garden Soil!
Whether planting your first garden, or gardening in the same familiar spot you have for years – planting a green manure crop early this spring can be just the ticket to recharging your soil for a great summer crop of vegetables!
What is a green manure crop?
Growing Vegetable plants like these tomatoes take a heavy toll on soil nutrients – and a green manure crop can help recharge your soil!.
Although you may think the term “green manure” has to do with something a little less appealing – in reality – it’s simply a cover crop that is grown specifically to be turned right back into the soil to return valuable nutrients to your garden.
Growing and then “digging in” and turning back under a green cover crop has the same effect and benefit as adding loads of compost and manure to your soil – and it’s so easy to do!
A green manure crop can be sown in the early spring months (here in Ohio – anytime from late March to early April) and then turned under in early to mid-May a few weeks before planting your garden. They are a great “quick” choice to build soil strength, especially for those that did not plant a fall cover crop or have access to a lot of compost.
In its fresh and growing green state, a cover crop such as annual rye, buckwheat or clover is loaded with valuable nitrogen and additional nutrients. Once turned over, the green manure crop starts to break down – and slowly releases its energy back into the soil to provide those nutrients for the new crops all summer long.
They are also perfect for keeping your soil in tact through strong spring storms, helping to eliminate soil loss from erosion. Even better – it prevents stray weed seeds from blowing in and settling into bare soil – making for a less weedy garden this summer!
Planting Your Cover Crop:
In early spring, as soon as the soil begins to thaw enough to gently rake the surface (usually mid March or early April here in Ohio), sow a generous amount of cover crop seed on your garden or raised bed soil. No need to disturb the soil with heavy digging or tilling – just simply raking the top 1/8″ of soil will allow enough space for the cover crop to germinate. No need to worry about freezing temperatures at night – the seed and crop will not be harmed – and will begin to grow as soon as the temps begin to climb in the Spring.
As mentioned above, annual rye, clover and buckwheat and are excellent choices for green manure crops because they can germinate and begin growing in as little as 7 to 10 days. Within a four-week time frame, you can have a thick stock of growing “green” manure” for your soil.
Then, a few weeks before you are ready to plant your main garden stash of tomatoes, cucumbers, peppers and more, (late May here) simply turn the cover crop under with a pitchfork or shovel – and plant!
It is important to let the soil rest a few weeks after turning the cover crop to allow the green manure crop to decompose a bit before throwing in your plants – although – we have planted after turning in just a week with no harm to our summer crop.
So get out there and plant a garden-soil energizing cover crop this Spring!
For more information on all types of cover crops, see our article : Cover Crop Basics
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Types of green manure
There are many types of green manure or different crops that can be used as green manure. Its convenience will depend on the specific details of our climate and soil, as well as the season in which we want to prepare the green manure or the crop that interests us after this.
The most common is to use legumes, due to their ability to fix atmospheric nitrogen thanks to their relationship with rhizobia, beneficial bacteria. However, the selection of plants for green manure is very wide. These are some of the most used:
Fabaceae or legumes
As we have said, these are the most commonly used for their ability to fix nitrogen in the soil. It is common to use vetches, lupins, clovers, beans or peas, among many others.
Grasses for green manure
Grasses tend to give very good results, especially when combined with some legumes. A widely used combination is that of oatmeal and vetch. It is also common to plant Italian rye or rye.
Crucifers such as turnip, cabbage, rapeseed and mustard are also very good options and the latter, in fact, is one of the most used. This is because it has roots with high branching capacity and rapid growth. Mustard roots are very spreading and breaking up the soil, leaving it looser and finer, which helps its oxygenation and the development of the crop that follows it. In addition, in winter it dries by itself, so if we plant it at the end of summer or in autumn, it will not even be necessary to mow it. Another advantage of mustard is that it keeps some garden pests at bay.
There are also other cruciferous plants that can be used to prepare and enrich the soil. The Russian comfrey is well known for its great capacity for growth and creation of plant mass. It is widely used in the production of slurry and compost , and even in the production of mulching or mulching .
Buckwheat is a great option when we want to treat very impoverished soils, and facellia has the ability to attract bees and bumblebees, with all the benefits that this entails.
Planting Green Manure Crops
When To Plant Green Manure Crops
A green manure crop can successfully go in the ground at any point during a growing season. Depending on the crop selected, the entire process can go from seed to “harvest” in as little as 4 to 6 weeks. The harvest,of course, being the moment the crop is cut down and reincorporated into the soil.
Unlike most garden crops, a green manure crop provides all of it’s resources back to the soil. Many gardeners plant these recharging crops in open spaces after harvesting spring or mid-summer crops. This allows plenty of time for fall planting in the same space.
But that fast growth and quick turnaround also makes a green manure crop perfect for planting and recharging your entire garden space in the early spring too. And what could be better than giving your soil a big boost before summer garden season!
Planting Early Spring Green Manure Crops
The foliage of a green manure crop can provide a big dose of nutrients when incorporated back into the garden. In addition, the roots of green manure crops help to loosen the soil as they grow and develop.
In most areas, there is ample time to plant a spring green manure crop before the main garden season begins. The key to success for early spring planting all begins with selecting the right crop for the job. Most notably, seeds and crops that will germinate and grow well in cool soil and cooler temperatures.
Two of the best choices for early planting are peas and clover.They both tolerate cooler soil and air temperatures well. In addition, they germinate and grow quickly, providing a quick cover in as little as 2 to 3 weeks. We’ll cover more on both of those later in the article, but for now, let’s take a look at the when, where and how of planting.
When & How To Plant Early Spring Green Manure Crops
In addition to traditional open field tilled garden spaces, manure crops can also be grown in raised bed and raised row spaces. In fact, when it comes to raised beds, they can be an easy way to recharge and add nutrients to soil that is otherwise left to fend for itself.
Green manure crops can be sown as soon as the soil thaws in your area. A few frosts, a bit of snow, or even a light freeze will not hurt crops like peas. In fact, quite often the cooler weather will spur a bit more growth.Recharging the soil with a green manure crop in the early spring sets the stage for a great garden season. As the plant matter decomposes, its energy is given back to the summer crops.
To plant, gently rake the surface and sow your seed of choice on top. There is no need for tilling or for heavy disturbing of the soil. Rake the seed gently after sowing to settle it in, and let Mother Nature take over. There is no need to cover the seed completely.
Depending on weather and spring conditions, the crop should begin to germinate and grow within a few weeks. Within four to 6 weeks, there should be a good covering of the surface of the soil. Allow your green manure crop to grow until a few weeks before you are ready to plant your main vegetable garden.
Turning Crops Over / Mowing Crops Off
Then, simply turn the cover crop under by tilling or turning it with a spade for smaller spaces. If you are working in a no-till environment, you can mow off the crop and allow it to simply decompose on the surface soil.
Depending on what seed you have chosen, you may have to mow the crop off a few time to allow it to stop all growth. Either way, the crops nutrients are left in the soil, recharging it as they decompose.
Peas are one of the few crops that actually help to improve nitrogen levels in the soil. As they grow, their roots help to fix nitrogen levels, making it available for the next crop.
The Best Seed For Early Spring Green Manure Crops
Although there are many great choices such as annual rye, alfalfa and hairy vetch for mid summer green manure crops, planting an early spring green manure crop requires cool weather loving crops. And as mentioned, field peas and clover and even alfalfa are big winners in that category. Here is a quick look at each along with seed links.
Peas are an excellent crop to grow to replenish available nitrogen in the soil. The crop is not only a cool weather survivor, it actually grows better in it! The roots are excellent at digging into the soil, and also add structure and biomass as they decompose. Simply till or dig in two weeks before planting your regular vegetable garden crops. Peas will die back after mowing a few times, making them excellent for no-till gardening too. Product Link : Dundale Pea Cover Crop Seed
A wondrous fixer of nitrogen in the soil, crimson clover is a great choice as a cover crop for those who grow tomatoes, corn and peppers. It germinates and grows thick quickly to snuff out competing weeds as well. Crimson clover is a great choice in-season as well between spring and fall plantings. Seed Link : Crimson Clover Seed
Alfalfa is one of the best green manure crops around for full season use. It germinates fast, and provides a thick covering of the soil. It also tolerates cooler temperatures, making it perfect for colder climates. Alfalfa grows well in all soil types, including poor soils. It is also highly drought tolerant. Avoid planting in overly wet conditions, and never allow it to flower. If the crop grows too big, simply mow down to keep seed heads from forming. Product Seed Link : Alfalfa Seed
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Sowing Green Manure Crops
Almost all of the green manure crops mentioned in this article can be directly sown into prepared soil by hand-broadcasting. When doing so, under broadcast at first, so you'll have some seed left to fill in any gaps. Then gently chop the seed into the soil by poking holes in the area with a rake. You may also want to tamp the soil down with a wide board to eliminate excess air spaces. Finally, water the area thoroughly.
Some of the crops will produce more, and more quickly if you first sprout them in soil on 1 inch centers in growing flats. After 5 to 10 days, when the seedlings are about 1-1/2 inches to 2 inches tall, transplant them into the garden. This works well with cereal rye, alfalfa, hard red spring wheat, barley, and oats — all of which set out on 5 inch centers.
Banner fava bean seed should be directly planted on 7 inch centers, and foul muddammas fava beans should be directly planted on 6 inch centers.
EDITOR'S NOTE: Ecology Action sells seed for all of the above-mentioned green manure crops, in allotments big enough to cover 100 square feet. Alsike clover, fodder radish, and agricultural mustard cost 80 cents each per allotment . . . barley and oats cost 90 cents each . . . cereal rye, alfalfa, and hard red spring wheat cost $1 each . . . wooly pod vetch costs $2.50 for one allotment, $3.50 for two, and $5 for three . . . banner fava beans cost $4, $7, and $10 for one, two, and three allotments . . . and foul muddammas fava beans cost $4, $6.50, and $9.50 for one, two, and three allotments. (Jeavons suggests you reduce your fava bean cost by buying just one unit and saving your own seed for later plantings.) All prices are postpaid from Ecology Action,Willits, CA.
John Jeavons was the subject of THE MOTHER EARTH NEWS feature interview in issue 63, in which he explained how his biointensive (also called biodynamic/French intensive) growing techniques could help combat world hunger. He is the author of one of our all-time favorite gardening books, How to Grow More Vegetables ($10.50).
Jeavons' nonprofit small-scale food research group also publishes The Backyard Homestead, Mini-Farm & Garden Log Book ($10.50) for those who want to become more effective food growers . . . One Circle ($9.50), by David Duhon and Cindy Gebhart, a guide to producing a complete year's diet in as little as 1,000 square feet . . .and Growing to Seed ($3.75), a 70-page booklet on seed saving. Again, all prices are postpaid from Ecology Action.