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.
By Pat Hitchcock, U. C. Master Gardener of Napa County
This winter seems to be a promising one; it's raining regularly. But along with the filling reservoirs and green hills come a multitude of weeds.
University of California Agriculture and Natural Resources publishes “Weed Pest Identification and Monitoring Cards” (Publication 3541) that identify nearly 50 different broadleaf and grassy weeds common in California. The cards have pictures of the plants at different stages of growth, as well as information on how they spread, where they grow and how to control them. Alas, most of them grow well on my property.
Weeds can't grow without water. Once the rains begin, they sprout from seeds or emerge from their dry-season dormancy. I was curious as to where they originated and why so many thrive here, so I began researching. It is daunting to discover that the weeds in my backyard come from all over the world.
Take dandelions (Taraxacum officinale). There are native American versions, but the more widespread dandelion was imported from Europe as an edible and medicinal plant. Today, most of us consider it a weed, although some people still enjoy it as a cooked green or salad.
Another common edible weed is purslane (Portulaca oleracea), a succulent summer annual with small yellow flowers. Purslane has been eaten throughout Europe, Asia and the Middle East since prehistoric times, but when it arrived in the New World is unclear. It makes a lemony addition to salads.
Several annual grasses thrive in Napa Valley winters, including Italian ryegrass (Lolum multiflorum), wild oat (Avena fatua) and ripgut brome (Bromus diandrus). These appear to have originated in the temperate regions of Europe but are widespread in our grasslands, parks and farmland. Besides taking over cultivated soil and crowding out garden plants, some have troublesome seeds that catch on pet fur or clothing and work their way into flesh. Pet owners know what misery these so-called “foxtails” can cause dogs and cats.
One of the most persistent weeds in my garden is field bindweed (Convolvulus arvensis). This perennial plant originated in Europe and Asia and most likely arrived with crop seeds in the 1700s. It quickly became invasive. Roots can grow as deep as 10 feet and prefer moist, fertile soil. That pretty much describes my vegetable beds; no wonder I am constantly pulling and digging this plant out.
Redstem fillaree (Erodium cicutarium) is a plant I loved as a child. I liked to pick off the drying seed head and watch it coil when separated from its flower. Now, as a gardener, I find its ability to stick to clothing, especially socks, truly annoying. Native to the Mediterranean basin, this plant is edible, but the leaves are best eaten young.
Mustard (Sinapsis arvensis) is another weed originating in the Mediterranean basin. Legend has it that the Spanish padres deliberately sowed mustard along El Camino Real to mark the way. More likely, this plant arrived in North America accidentally like so many others.
Wild radish (Raphanus raphanistrum) is related to mustard.Native to Asia, it has spread all over the world. According to the weed I.D. cards, it is similar to Raphanus sativus, the common radish, and hybridizes easily with it. Both have four-petal flowers that may be white, yellow or pale purplish-pink. They bloom in early spring and continue as late as July, producing a lot of seeds over several months. Seeds can remain viable in the soil for 30 years, so preventing seed production is one key to controlling the weed.
Redroot pigweed (Amaranthus retroflexus) is another apparently edible weed in our region. It is native to the tropical Americas but has naturalized all over the world. An annual plant, it spreads by seed that can live up to 40 years.
Prickly lettuce (Lactuca serriola) is an unattractive plant with prickly leaves and stems and bitter sap. Who would guess that it is the nearest wild relative of our common garden lettuces? It appears to have originated in Europe, Asia and North Africa, and ancient Greeks and Egyptians used it.
Some say that a weed is any plant in the wrong place. The weeds I researched thrive all over the world due to their ability to out-compete other plants for water, sunlight and nutrients. Controlling weeds is important both in cultivated gardens like my vegetable patch and in natural areas where they can crowd out native plants.
As the I.D. cards suggest, the best way to control most weeds is by manually removing them before they can bloom and produce seed. Another word for that is weeding. Winter is a good time to get out there and enjoy, I mean control, your weeds.
Workshop: U. C. Master Gardeners of Napa County will hold a workshop on “Fruit Tree Pruning and Grafting” on Saturday, January 21, from 9 a.m. to 2 p.m., at the University of California Cooperative Extension office, 1710 Soscol Avenue, Napa. The dormant season is the best time to prune your deciduous fruit trees to increase vigor. Join the Master Gardeners fruit-tree team for this workshop showing techniques to develop healthy and productive fruit trees. A local expert grafter will give a grafting demonstration. The afternoon field trip offers home gardeners the opportunity for a hands-on experience. Dress for seasonal outdoor weather and bring your pruners. Online registration (credit card only); Mail-in registration (check only or drop off cash payment)
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.