Planning for next growing season begins now: Cover crop options after harvest of early vegetables

Editor’s note: This article is from the archives of the MSU Crop Advisory Team Alerts. Check the label of any pesticide referenced to ensure your use is included.

A successful cropping system should take advantage of the available windows of opportunity to integrate cover crops in the production system. For growers in Michigan (and other regions with a temperate climate) who cannot afford to skip an entire summer to grow cover crops, there are multiple options for fitting cover crops into their rotation. These include spring planting before the main crop and late summer planting after harvest of an early crop. In both cases, cool season cover crops like Brassica species and oats are appropriate.

Late summer Brassica cover crops

Late summer planting of Brassica cover crops runs from late July to late August. In Michigan, the success of Brassica cover crops planted after August 25 has been variable depending on the weather. Germination and early growth is severely affected under cool and dry conditions. Potential problems with late planting include low biomass production and successful overwintering of young plants (especially under mild winters). The Brassicas are more susceptible to frost at flowering stage and growers relying on frost to kill the cover crops should avoid planting too late. For the above reasons, it is better to plant Brassica cover crops in mid August to optimize their benefits. The seeding rates of some of the Brassica cover crops are indicated in Table 1. High density planting leads to excessive competition between plants and results in low total biomass production. Also, optimum seeding rate varies depending on the cultivar used. For example, oilseed radish “Daikon” and “Defender” should not be seeded at the same density. Part of this difference is related to seed size; Daikon seed is usually larger than Defender seed. Therefore, with the same weights the number of seeds planted is higher for the cultivar with smaller seed size.

Late summer oats cover crop

This is a low cost cool season cover crop that establishes well in late summer and early fall. It germinates quickly, therefore preventing weeds from growing and setting seed. Oats recycle significant amounts of excess nutrient left after harvest of the main crop. Under adequate growing conditions, late summer/early fall planted oats can produce up to 4,000 pounds of dry matter per acre. To maximize biomass production, oats should be seeded at least 40 to 60 days before the first killing frost. Seeding rate is 3 to 4 bushels per acre. The seed can be broadcast and disked lightly for incorporation.

For all cover crops, it is critical to make sure that the herbicides used in the previous main crops are not problems. Residual herbicides may cause injury to the cover crops.

Additional information on these cover crops can be found at the following web links:

Table 1. Suggested planting density of some Brassica cover crops for optimum biomass production.

Oilseed radish “Diakon”
Oilseed radish “Defender”
Brown mustard
Oriental mustard
Yellow mustard

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