Many growers are trying cover crop mixtures, both of their own making and those sold by various vendors. Some mixtures work well while others have better marketing than effectiveness. Here are simple concepts that can help decide whether to use a mixture, and which mixture provides the most benefit.

Think of assembling a cover crop mixture the same way you assemble a team. This “team” approach can accomplish more goals than any one member is good at alone.

The most effective team has:

• The best member available for each goal, and
• Members who get along.

The process of building a cover crop team involves three steps:

1. What are your top management goals?

Answering this question may be the hardest step. Weed suppression, erosion control, nitrogen management, and feeding the soil are usually near the top.

2. What is the best member for each goal?

For each goal, the best cover crop option depends on the season, fertility, moisture, and other local factors. Use only the best option. Doubling or tripling up mix components towards one goal reduces the mixture’s overall effectiveness because the weaker components make it hard for the strong one to do its job.

3. Do they get along with each other?

A good cover crop mixture has components that:

• • Don’t suppress each other.
  • Stimulate the main function of the other mix components.
  • Fill the space at different times.
  • Will all be terminated before the next crop is due to be planted.

Success with cover crops always requires killing on time—this requirement is harder to accomplish with mixtures. Each component must either die without making seeds or be at the optimum growth stage for termination when the cover crop needs to be killed.

An example of complementary mixture behavior is an overwintering cover crop that contains components that winter kill (like oats, mustards, or radishes) to allow other components (like vetch or clover) to grow well in the spring.

The components should work reliably even in the mixture. If you count on oats to winter kill, it is important not to have another component in the mix grow so large that it protects the oat crowns from the winter cold.

Some complementary mixtures—mostly grass and legume:

• Rye + hairy vetch for September planting achieves many winter goals.
• Wheat + hairy vetch + radish for August planting recovers and fixes nitrogen for the next crop.
• Annual Ryegrass + medium red clover planted any time provides medium–term weed suppression and nitrogen fixation.
• Sudangrass + Sunn hemp in whole–summer planting adds nitrogen and biomass.

Some cover crops don’t mix well. Buckwheat is a great cover crop for weed suppression. But buckwheat does not get along well with others. It somewhat suppresses other mix components before going to seed first to become a weed in the next crop. Buckwheat in a mixture also fails to suppress weeds, because it only succeeds at that when it forms a complete cover canopy that smothers weeds—individual buckwheat plants in a mix cannot do that.

Buckwheat being a weed in a clover-phacelia mixture. If phacelia needs a nurse crop, use oats.