Extension

Shelby Mendoza, Assistant Manager for the OSU Student Farm

If you don’t plan to use your vegetable garden this fall, now is a great time to plan for planting cover crops. Cover crops can seem intimidating if you’ve never tried them before because there are so many options and a lot of information online. Really, though, it comes down to finding a mix that works for your situation—your location, your soil’s needs, and when you plan to plant your next round of vegetables.

Why Use Cover Crops in a Vegetable Garden?

The benefits depend on which species you choose, but in general, cover crops can:

• Reduce soil erosion
• Suppress weeds
• Improve soil fertility by adding nutrients back into the soil
  

Good Fall / Winter Cover Crop Options for Oklahoma Gardeners

For most situations, a mix of a grass and a legume is recommended. Together, they suppress weeds, build soil organic matter (which improves soil structure, water infiltration, and nutrient retention), and add nitrogen to the soil.

Grasses

Hard Red Winter Wheat

• Erosion control
• Suppresses weeds
• Scavenges nutrients, bringing them higher into the soil profile
• Adds biomass that becomes organic matter when incorporated
• Easy to turn in with a broad fork or pitchfork
• Should be killed 2–3 weeks before planting the next vegetable crop

Oats

• Suppresses weeds
• Prevents erosion
• Scavenges excess nutrients
• Adds biomass for organic matter
• Winterkills after a heavy frost

Legumes

Legumes fix nitrogen through a symbiotic relationship with Rhizobia bacteria in the soil. This relationship allows legumes to convert atmospheric nitrogen into a plant-available form. Some legumes require an inoculant to achieve optimal nitrogen fixation. Once you have chosen a legume cover crop, check whether an inoculant is recommended for that species.

Crimson Clover (Trifolium incarnatum)

• Adds nitrogen
• Prevents erosion
• A pollinator favorite in early spring
• Adds biomass for organic matter

Hairy Vetch (Vicia villosa)

• Adds nitrogen
• Suppresses weeds
• Prevents erosion
• Improves topsoil tilth for the following vegetable crop
• Can reseed on its own
  

Tilth is the physical condition of soil, determined by its structure and suitability for plant growth. Good tilth feels crumbly, allowing for root growth, water infiltration, and aeration.

Other Options

Daikon Radish (Raphanus sativus longipinnatus)

• Breaks up compacted soils
• Suppresses weeds
• Scavenges nutrients
• Winterkills, releasing nutrients it absorbed back into the soil

Terminating Cover Crops

Timing of Termination

• Cover crops should generally be terminated 2 - 4 weeks before planting your next vegetables.
• This gives time for residues to break down and prevents them from tying up nutrients that your vegetable crops need.

Methods of Termination for Home Gardeners

• Cutting / Mowing - Cut plants at the base with shears, a mower, or even a weed eater. Leave the residue on the soil surface as mulch or incorporate it into the soil.
• Tilling / Incorporating - Turn crops under with a tiller, broad fork, or spade. This helps residues decompose faster but disturbs soil structure more than leaving mulch.
• Winterkill - Some covers (like oats and daikon radish) naturally die after heavy frost, so no action is needed.

Things to Watch For

• Residue Breakdown - High-carbon grasses (like wheat) take longer to decompose. Mixing them with legumes helps balance decomposition.
• Nutrient availability - Incorporating green cover crops too close to planting can cause temporary nutrient tie-up or cooler soil conditions, which may slow  vegetable growth.
• Self-seeding - Some species (like hairy vetch) can reseed if not terminated before flowering.