Planting Cover Crops Enriches the Soil.
By T. Eric Nightingale
UC Master Gardeners of Napa County
The long summer of vegetable gardening can leave your soil in need of some rejuvenation, a perfect job for cover crops. Also known as “green manure,” cover crops are a natural and easy way to keep your garden soil healthy. They return nutrients to the soil, improve soil texture, prevent weeds and reduce erosion. The most effective and frequently used cover crop plants are legumes, grasses, grains and brassicas.
Returning nitrogen, a primary plant nutrient, to the soil is possibly the most important role of cover crops. Legumes are extremely good at this. They nurture Rhizobia, bacteria that converts nitrogen in the air into ammonia. Plants can later process this ammonium to obtain nitrogen from it. Rhizobia can't live in the soil on their own, however, so they use the roots of certain plants as a host. Some companies even sell seed with Rhizobia added to the mix. Legumes used as cover crops include fava beans, hairy vetch and clovers.
Brassicas such as radish and mustard are widely used as cover crops in vineyards. You have probably seen them flowering around Napa Valley. These plants grow deep (sometimes as deep as four feet), strong roots that break up the soil, letting water flow deeper into the ground.
Well-hydrated soil not only helps your plants, but allows for more soil organism activity. Grasses such as barley and ryegrass also help to break up the earth, but also allow for the introduction of high amounts of organic matter when they are turned back into the soil. It is common to use many different types of cover crops, in a mix, to provide as much benefit as possible to your garden.
Helping to retain moisture, improving soil texture and increasing fertility all contribute to a robust soil ecosystem. When this system of microbes, fungi, bacteria and other organisms is functioning as intended, the likelihood of soil-borne diseases greatly reduces. Even a garden needs to eat its greens to stay healthy.
Fall is a great time to plant cover crops, since many gardeners take a break between vegetable crops. You can sow cover crops directly from seed, broadcasting them by hand over the soil after tilling it lightly. Cover the seeds with a thin layer of soil to protect them while they germinate. You can add a small amount of fertilizer to give the young plants a jump-start on life. You will get a large return on this small investment when the plants grow.
Cover crops can also be used in the summer. Grasses such as sorghum, soybean and cowpea are often grown at this time. Also used are buckwheat and sunflower, giving the added boon of attractive flowers.
When the cover crops are at the end of their lives or you want to plant something else, turn them into the earth. Their organic matter will break down and further improve the soil. Alternatively, you can mow them and leave them on top of the soil as a mulch. They will eventually decay but in the meantime will further decrease water loss and erosion.
Cover crops also suppress weeds by blocking the sunlight, keeping weed seeds from germinating. If they are left on the soil surface as a mulch, they continue their weed-prevention duties. Some cover crop flowers feed bees, and fava beans, a popular cover crop, are edible and delicious.
There has been extensive research and testing on cover crops in recent decades. Their wonderful features make them sound like a cure-all for anything that ails your soil. In truth, they are one of many contributors to a healthy and productive garden. There is no doubt, however, that any garden will benefit from cover crops.
Workshop: U. C. Master Gardeners of Napa County will hold a workshop on the different kinds of poinsettias and other potted plants for holiday decorating using color and shapes. The workshop will be held on Thursday, December, from 7:00 p.m. to 8:00 p.m., at the Napa County Library, 580 Coombs Street, Napa. This is a free workshop and registration is not required.
Master Gardeners are volunteers who help the University of California reach the gardening public with home gardening information. U. C. Master Gardeners of Napa County (http://ucanr.edu/ucmgnapa/) are available to answer gardening questions in person or by phone, Monday, Wednesday and Friday, 9 a.m. to Noon, at the U. C. Cooperative Extension office, 1710 Soscol Avenue, Suite 4, Napa, 707-253-4143, or from outside City of Napa toll-free at 877-279-3065. Or e-mail your garden questions by following the guidelines on our web site. Click on Napa, then on Have Garden Questions? Find us on Facebook under UC Master Gardeners of Napa County.
This month there are some wonderful opportunities to learn about, buy and plant natives. Our wet winters and dry summers are features we share with Mediterranean countries, and Napa native plants have learned to adapt to these conditions.
Many plants in the wild go dormant in the summer to conserve water, while others have leaves that deflect the summer heat to conserve what moisture they can glean. Native plants are diverse in type, from ground covers to tall trees. They are often water wise and deer resistant.
Natives can attract pollinators, birds and butterflies; fill difficult areas of your yard; and bring interest, color and even edibles to your garden.
If you are thinking about replacing a thirsty lawn, consider replanting with native grasses or grass-like plants. Native grasses have much more extensive root systems than typical turf grasses, so they are able to dive deep for moisture and nutrients during Napa’s long dry summers.
Grasses clean the air and sequester carbon deep in the soil. Deeply rooted grasses minimize erosion, soften the impact of rain water on soils and are part of the natural environment for native butterflies and birds.
To learn more about these underappreciated natives, join Bob Hornback, aka “The Grassman,” on Wednesday, April 10, from 7 p.m.to 8:30 p.m. at the Social Hall at Skyline Park in Napa. This event is sponsored by the Native Plant Society. For more details, call 707-253-2665 or visit www.napavalleycnps.org.
Planting under deciduous oaks or in partial shade can be a challenge, but here, too, natives offer some surprising choices. Consider currants such as Ribes sanguineum, a red currant with a cotton candy-pink flower. I planted several of these currants last year, and they are blooming beautifully in my garden now. Ribes ‘White Icicle’ is a white-blossomed albino currant; R. speciosum (fuchsia-flowering gooseberry) is a gorgeous currant, four to five feet in height, with deep pink, fuschia-like blossoms in spring.
Currants can take full sun, although in hot areas they appreciate some afternoon relief. They do well in partial shade, and some can grow six feet tall. Plant them where they will have room to thrive. Jam and jelly makers: water carefully to maximize your harvest. A mature bush can produce six to ten pounds of fruit in a season. Black currants are generally sweeter, while red and white currants may require a tad more sugar to balance their tartness. All make wonderful preserves.
For spring color, U. C. Davis native plant expert Kendra Baumgartner suggests white, blue and yellow Douglas iris (Iris douglasiana). They are deer resistant and bring color to shadier areas. These tough perennials grow back each year from thick white roots. You can divide them every couple of years to brighten more of your garden or to share with friends. Douglas iris are drought resistant, too.
For hot, sunny areas, consider Mimulus cardinalis (red monkeyflower). Its bright red flowers attract hummingbirds, and it is drought resistant and care free.
To see these and other natives, mark your calendar for the California Native Plant Society’s spring plant sale on Saturday, April 13, and Sunday, April 14, at Skyline Park. Call 707-253-2665 for more details.
When you arrive for the sale, stroll around the Martha Walker California Native Habitat Garden to see these beautiful plants in a garden setting. More than 200 native plants thrive in this special garden and are identified with markers. A walk through the Martha Walker Garden will give you an accurate picture of how large that small plant you just bought might grow.
Experts will be on hand to answer questions, and all proceeds go toward maintenance, improvements and educational programs in the park. Admission to both Skyline Park and the Martha Walker Garden is free during the sale.
Workshop: Napa County Master Gardeners will host a workshop on growing tomatoes on Saturday, April 13, from 9:30 a.m. to 11:30 a.m. at the Yountville Community Center, 6516 Washington Street, Yountville. Learn about tomato varieties that work well in Napa County. Learn when and how to plant; how to stake, water and feed; and how to handle common tomato pests and diseases. Register through Yountville Parks and Recreation: Mail in or Walk in registration (cash or check only). For fee and additional workshop information, (707) 944-8712 or visit the web site.
Master Gardeners are volunteers who help the University of California reach the gardening public with home gardening information. Napa County Master Gardeners (http://cenapa.ucdavis.edu) are available to answer gardening questions in person or by phone, Monday, Wednesday and Friday, 9 a.m. to Noon, at the U. C. Cooperative Extension office, 1710 Soscol Avenue, Suite 4, Napa, 707-253-4143, or from outside City of Napa toll-free at 877-279-3065. Or e-mail your garden questions by following the guidelines on our web site. Click on Napa, then on Have Garden Questions?