The Norman Transcript

September 20, 2013

Give veggie gardens a break with crops


The Norman Transcript

NORMAN — Picture a plant root that reaches 12 inches into the soil. What happens when it decomposes? Organic matter (beneficial composted materials) is increased. this, in turn, feeds billions of soil organisms.

In addition, these soil voids create an avenue for water, air and nutrients to infiltrate the soil. Soil is a living body that must be nurtured to be productive. Otherwise, water and nutrients run off, soil erodes and fertility is depleted.

Cover crops can add back to the soil after a season of use. Think of cover cropping as a vacation for the soil, a time to relax and recharge for the upcoming season. Now is the perfect time for a winter cover crop in a traditional or raised vegetable garden.

The surface of earth doesn’t like to be naked. Mother Nature prevents this from happening by covering herself with annual grasses and weeds, if exposed. If you usually strip the surface of your garden by tilling, I encourage you to think twice.

Frequent tillage not only exposes the soil surface and brings weed seeds to the surface for germination, but it also causes nutrients to be lost and degraded while destroying beneficial microorganisms. Tillage creates a human-dependent soil, prone to erosion, compaction, nutrient depletion and soil-borne organism reduction.

Cease tilling to prevent unwanted weeds and begin to build a functional, healthy soil. Intentionally planting a cover crop will outcompete weeds before taking hold, and I highly recommend that all gardeners keep something growing year-round.

Cover crops can be adapted for use in the garden and serve many beneficial functions, which I can only begin to cover here. Cover crops can be a trap crop for insect pests and reduce nematode numbers. But they also can attract beneficial insects and pollinators.

Covering the soil will cool and preserve it, decreasing the need for irrigation and weed management. Cover cropping also serves as a rotation to break the cycle of planting the same things year after year. Rotating the cover crops themselves is just as important as rotating your vegetable species from one year to the next.

Legumes are the best choice, giving you the most bang for your buck. Legumes include crops like beans, peas, clover, vetch and alfalfa. Since nitrogen is readily used and released from the earth, most soils are deficient in this macronutrient at some point.

When inoculated with species-specific Rhizobial bacteria, legumes form nodules on their roots that fix nitrogen from the atmosphere. Where other types of plants and cover crops continue to mine the soil of organic matter and nutrients and take it away, legumes add back, creating a fertile, healthy soil.

Always inoculate your legume seeds, or make sure they are inoculated with the proper strain of bacteria when purchasing. Most seed and feed stores will have the proper bacteria for purchase, or you can buy online. Good choices for winter cover include Austrian Winter Pea, Crimson Clover, Red Clover, Arrowleaf Clover, Hairy Vetch and Fava Bean.

Root crops for winter cover include turnips, radishes and beets. Root crops penetrate deeply into soil, bringing unusable nutrients to the surface for use and breaking up plow pans and compacted soil. When allowed to rot in place, these root crops add an abundant amount of organic matter to the soil.

For heavily compacted soils, winter root crops like tillage radishes are a good option. If you need a ground-buster for summer, try deep-rooted sunflowers to pierce hard pans.

The most popular cereal crops for winter cover include wheat, rye, barley and oats. Cereal grains form massive root systems and top growth, creating an abundance of biomass. These roots can infiltrate a tremendous amount of soil but also may rob it of nutrients. They require a tremendous amount of nitrogen, as opposed to inoculated legumes, which make their own nitrogen.For the gardener practicing modified no-till, I don’t recommend these crops unless planted with an inoculated legume like clover or winter peas.

Cover crops can be planted by inoculating their seed and sowing from mid-September until the end of October, depending on soil moisture. Prepare the area by ensuring the seed has optimal seed-to-soil contact and always time your planting around a rainfall event.

Move aside mulches before seeding, and broadcast one to two pounds of seed per 1,000 square feet of garden. Legumes do not need fertilizer applications of nitrogen, but may require phosphorous or potassium. A soil test is the only way to know for sure what you need to apply (if anything).

Other crops like wheat may need one to two pounds of nitrogen per 1,000 square feet. Lightly cover the seed with a rake, and make certain you have a firm seedbed before planting because many cover crops, like clover, have tiny seeds that will die if they are planted too deep.

If your foot sinks in your garden more than half an inch, your soil is too fluffy and you need to firm it. Use a drip hose or a light sprinkle of water to keep the soil surface moist until germination. As always, conserve moisture by watering in the early morning.

Cover crops act as living mulch that can be prolonged into the growing season. When ready to plant this spring, simply string trim or clear a small area for individual plants among the growing cover crop.

The legumes will continue to fix nitrogen that tomatoes, cucumbers or onions will use. Some recommend removing the crop before flowering, but leaving the plant is not detrimental to the garden and will attract pollinators.

Tilling in a cover crop can be done but adds another step and is not recommended for optimum soil health. Planting legumes and allowing the plant to die back and decompose naturally into the earth will keep the soil, beneficial microbes and earthworms happy. This will produce a vibrant and productive garden that is diverse and healthy.

Tracey Payton Miller is Cleveland County’s horticulture extension educator for the Oklahoma Cooperative Extension.