Cover Crop Questions and Answers

Cover crops are a hot topic these days. There is always the usual seedings of red clover in winter wheat in the spring and other cover crops after wheat harvest. Cover crops are increasingly being planted in many other situations. Interest is growing in interseeding cover crops into seed corn, silage corn and grain corn. Cover crops are also being seeded after silage corn, edible beans and early harvested soybeans.

There are many reasons to plant cover crops, including scavenging nitrogen from the soil or tying up nitrogen after a manure application. Cover crops can help suppress weeds, reduce nematode populations, improve soil structure and help open up compacted soil. Most importantly, cover crops help protect the soil from wind and water erosion.

Some answers to some common cover crop questions:

What is the difference between the named oilseed radish brands (such as Tillage Radish, Tilth Pro NitroRadish, GroundHog Radish) and common oilseed radish?

A "named variety" is a variety or selection that has been refined for certain characteristics. Most selections currently available are a diakon radish. The chief characteristics of these are a large root and delayed flowering. Common seed oilseed radish is often a mixture of seed varying characteristics.. Seed will vary from year to year giving a range of root size, from small to large.

How late can I seed a cover crop?

Seeding dates for cover crops vary by crop type and region of the province. Winter cereals can be seeded later than those killed by frost. Cover crop success will be high for crops planted up until the end of August. In many areas, the risk of frost killing the cover crop before it has enough growth increases up until the middle of September. After the middle of September in southern Ontario, it is usually not worth planting cover crops like oilseed radish.

Why did my cover crop have poor growth?

Cover crops that scavenge nitrogen, such as oilseed radish, oats, mustards and spring wheat, when planted after winter wheat may not do well. These cover crops require nitrogen for growth and there may not be a lot of nitrogen left after the wheat crop. They often end up competing with volunteer wheat for what little nitrogen there is.

What about termination of the cover crop?

Many of the common cover crops are killed by frost so there is no need to terminate them. There are a few cover crops that could provide some surprises. The first is annual ryegrass. The name is a bit misleading as many of these will survive the winter. Usually it is terminated in the fall. If left until the spring, be aware that it can grow to 60 - 90 cm (2-3 feet) in height during a warm wet spell in the spring. The others are oilseed radish, buckwheat and the mustards. If they are allowed to go to seed, they could become a weed problem for years to come. Of course the winter cereals will have to be killed in the fall or spring depending on the situation.

Go to to find the Cover Crop Selector tool for information on planting, seeding dates and answers to many other questions. Think about cover crops as part of your cropping system, use the resources available to you and your chance of success will be much greater.

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