May 2024

For summer weed suppression, New York growers have a great management tool in buckwheat. Buckwheat has been proven many times to be the best weed-suppressing summer cover crop. Better than species that grow bigger, and better than any cover crop mix.

Buckwheat also provides valuable erosion protection against rain and mellows the soil for the next crop. For this article, those are just side benefits. Weeds are the likely to be the essential motivation for this cover crop.

In practice, buckwheat cover crops are often used to keep weeds from establishing in areas that have not been planted yet, as well as areas that have been harvested. Across a vegetable farm, sequential plantings and harvests often leave areas of open land that quickly become weed infested, replenishing that awful seedbank. Buckwheat is also helpful to suppress perennial weeds like quackgrass. It is even another way to kill some of the recent glyphosate-resistant weeds.

The weed-suppression mechanism is simple: buckwheat outcompetes the weeds. To succeed with a buckwheat cover crop, focus on making it win the competition against weeds.

Follow my tried-and-true keys to cover crop success:

Fast start. The goal is to have emergence from the soil on day 3.

• Use vigorous seed. Commercial seed is excellent, but barn storage will reduce vigor considerably in one year and too much in two years. Saved seed should be cleaned to remove weed seeds and keep only the fattest buckwheat kernels.
• Plant when the soil is warm enough: over 65°F average of day and night. In much of New York, that is after Memorial Day. Check the forecast.
• Plant into some soil moisture, but no deeper, and get the best seed-soil contact you can achieve.
• For buckwheat to outcompete the weeds, weeds cannot have a head start. Make sure all the weeds, even those in white-thread stage, are dead. A shallow cultivation during or just before planting can accomplish that.

No Gaps
A young buckwheat plant will suppress weed seedlings out about five inches. Therefore, any gaps bigger than 9 inches will get weedy. Whatever the seeding method, make sure the soil preparation and the seeding tools make a gapless stand. Uniformity is much better than just using more seed. Crowding makes the buckwheat plants smaller and less effective as a cover crop.

Kill on time.
Buckwheat’s value peaks at 35 to 40 days after seeding, both for weed suppression and active-carbon contribution. The time to kill is easy to see, because the planting turns from green to white with flowers. Put the termination date on the calendar just in case. Letting the buckwheat grow longer results in volunteer buckwheat seedlings in fall and spring. Those volunteers can be a problem because buckwheat is so competitive against crops as well.
Mowing is a common first step in termination. The residue dries in hours so the ground can be prepared with cultivation for the next crop or left to rest until the remaining area is ready.

This note was prepared for use by the Cornell Cooperative Extension Vegetable Program Work Team in publications in 2024. Others are free to reprint it with author credit.

Thomas Björkman, Professor Emeritus, Section of Horticulture Cornell AgriTech. Geneva NY