By early summer, many of us have pulled up our spent spring crops.  No disrespect to okra or lima beans, but sometimes we just don’t want to actively garden in the intense heat.  So what can we do with our garden beds instead?  We can grow cover crops and use them to build our long-term soil health.

These days many Florida home gardeners are familiar with solarizing beds during the heat of the summer.  Covering them with clear plastic for 6-8 weeks during the hottest months can kill many soil pathogens and weed seeds in the top several inches of soil.  Cover cropping is another option for improving soil between vegetable crops that is not as familiar, perhaps because it has typically been associated with large farms rather than home gardens.  Although the scale and implementation methods may differ, cover crops can be just as helpful in raised beds as in fields.

What is a cover crop?

A cover crop is anything we plant between vegetable crop seasons that we grow for a specific, typically non-edible, purpose.  Cover crops can be planted to meet a variety of goals: to prevent water or wind erosion of soil; to suppress weeds; to reclaim nutrients from the soil; to add nitrogen to the soil; or to provide habitat for beneficial insects and pollinators.  Our cover crop choices vary by season, but they tend to be grasses, grains or legumes.  Because of legumes’ ability to take nitrogen from the air, fix it in their roots with help from bacteria, they are often a first choice for gardens on sandy Florida soils.

What are my cover crop options?

The first step to planting a cover crop is deciding what your purpose is.  Each type of cover crop is good for some things and not so good for others.  Knowing your goals and choosing a crop that will accomplish them is the first key to success.  Paying attention to season is another important factor.  Some crops grow well in the hot season, and some grow better in the cool season.  There are not many that grow well in both.

UF IFAS has a list of recommendations for annual summer cover crops in Florida. (See the document Managing Cover Crops for Improved Soil Health for details.)  All are good in meeting specific goals. 

Several recommended cover crops that stand out for summer home gardener are:

• Iron Clay Cowpeas.  These legumes love the heat and are drought tolerant once established.  They have few, if any pests, and they grow and cover ground quickly.  They control erosion and weeds; suppress some types of nematodes, attract beneficial insects and scavenge phosphorus and potassium from the soil, while fixing nitrogen from the atmosphere.  In addition, they are easy to find in home garden centers.

  

• Sunn Hemp.  Despite the name, these legumes are not related to hemp and are not in the same plant family as cannabis.  They grow rapidly and produce large amounts of biomass, or oganic matter.  They have many of the same qualities as cowpeas, and they also produce allelopathic compounds that inhibit the growth of weeds.  These plants become woody as the plants grow tall, so it may be a good idea to trim them back at least once during the summer.  This will encourage more tender new growth.  And don’t wait too long to terminate them.

  

• Sorghum-Sudangrass.  This quick-growing, drought tolerant, annual grass is not a legume, so it does not fix nitrogen.  But it’s a great weed suppressor and erosion controller.  And it can help improve soil compaction and scavenge nutrients from deep in the soil, as well as benefiting insects.

If you’re still not sure which cover crop is right for your garden, you can also mix several crops to get the benefits of them all!

So, what do I do?

Once you’ve decided on your crop and purchased seeds, getting started is relatively easy.  The first step is to make sure your garden bed is crop, residue and weed free.  Then plant your seeds.  If you have a small area, you can use a dibbler to make impressions in the soil at your desired spacing and plant 1-2 seeds per hole.  Often, it’s much quicker and easier to simply broadcast seeds by hand.  Then rake over them lightly to ensure seeds make good contact with soil.  Then water the seeds in.  Check on them daily, and water as needed to keep the seeds moist until they germinate.

As cover crops begin to grow, you may need to water and weed occasionally, especially until they really get started and are able to suppress weeds on their own.  After that, however, cover crops should be relatively self-sufficient for the 60-90 days that we typically grow them.

How and when do I end the cover crop?

Timing of cover crop termination depends on when you are ready to plant your fall crops, as well as on the growth stage of your cover crops.  If you are growing them to maximize their biomass or nitrogen fixation, you’ll want to kill them just as they begin to flower, but before they begin to form seeds.  At that point, the plants are at their leafiest, and you won’t have self-seeding issues with your next vegetable crop.

How you terminate the crops depends on the size of your bed and the tools you have.  You can do this by mowing them, weed-whacking them or chopping them down, and then either turning them into the soil or leaving them on the surface.  Remember–if you want to benefit from the nutrients and organic matter in the next growing season, you need to leave them there.  Don’t put them in the compost or yard waste!  And finally, terminate them shortly before you plan to plant your fall crops.  If you wait too long, and we happen to get a hard summer rain after you’ve terminated, some of those nutrients may be leached out of the soil.

Keys to success

• Know what your goals for cover cropping are, and choose a crop that will help you meet them.
• Choose cover crops appropriate for your intended season.
• Give your cover crops attention at the beginning to get them established.  Then you can go on vacation!
• Terminate the cover crops in a way and at the time that will maximize your goals.

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