By Susanne von Rosenberg, UC Master Gardener of Napa County
It's May and everything is growing beautifully, including weeds. Even if your garden is exceptionally well-weeded, new invaders will creep in and demand attention. Our general reaction is to remove them as soon as we realize that we have them, and we think of a good, tidy garden as one that is free of weeds.
In general, until you are comfortable with weed identification, keeping your garden entirely free of things that you did not plant is a good approach. However, weeds can also provide some benefits, so learning about the different weeds can help you decide whether you just might let certain ones grow for a while. Over time, you may make friends with certain weeds and make them part of the cycle of your garden.
So what is a weed? Most commonly we consider something a weed if it is growing somewhere we don't want it to. Those California poppies you love in your flower beds just might be a weed if they start growing in your vegetable bed. I was surprised to learn that some people consider miner's lettuce, an edible California native that I carefully cultivated in my garden, a weed.
How can weeds actually be beneficial? Some weeds are edible, many can supplement your compost, and some help loosen the soil. They may provide erosion control and dust control. Some provide food or habitat for pollinators and other wild animals.
In addition, weeds can teach us about our soil. Certain weeds prefer specific soil conditions, so if you have those weeds, you can assume that your soil has those characteristics.
Common edible weeds include purslane, dandelion, lamb's quarters, nettles, fennel and chickweed. If you're not sure what you're looking at (you only know it's not something you planted), you can use the weed identification tutorials and information on the University of California Integrated Pest Management (UC IPM) site. If you're going to eat weeds (the ultimate revenge), use common sense. Never eat anything if you're not totally certain you've identified it correctly.
Many weeds make good additions to your compost or can serve as mulch. Annual weeds that have not developed flowers can be chopped up and left in place, although in winter and in moist areas of your garden, you have to make sure they don't re-root. You can also chop them and add them to your compost bin.
Those parts of perennial weeds that won't re-sprout can also be added to compost or used as mulch. With perennial weeds, though, it's important to know how they propagate so you don't inadvertently spread a problem. If a perennial weed has not flowered, you can also let it dry out completely (think completely crispy and brown) and then put it into your compost.
Some weeds improve soil by growing deep roots that break up the subsoil (the layer immediately below the topsoil). That allows the weaker roots of more delicate plants to access the water and nutrients there. Some common weeds with deep, strong roots include wild chicory, plantain, sow thistle and vetch, as well as lamb's quarter and purslane. Cut these weeds off at the soil surface before they start to flower. The roots will decay in place, adding organic matter to your soil. The tops can go into your compost. You'll get the most benefit if you keep these weeds fairly far apart; if they grow close together their roots won't penetrate as deeply.
Some weeds are great for attracting pollinators. However, you have to let the weeds flower. The mustard we see flowering in Napa Valley vineyards is one example. Fennel, wild radish and pigweed are other examples of weeds that are good pollinator plants. Pull them as soon as they have bloomed, and do not put the spent flowers in your compost.
Weeds can also act as living mulch. This feature can be particularly helpful in winter, if you are not growing vegetables or an intentional crop such as fava beans. Almost any annual weed can serve as living mulch. (You do not want to give perennial weeds the benefit of extra growing time.) Some annual weeds, such as chickweed and purslane, will form a mat as they grow and thus help suppress other weeds.
Finally, weeds give you clues about what is going on with your soil. Like other plants, weeds have specific soil preferences. Chicory, purslane and lamb's quarters are generally good news because they indicate rich soils. Thistles, wild turnip and bindweed, on the other hand, can indicate that you have compacted soil or a crusted soil surface. Poor drainage can be indicated by weeds such as sedges and Bermuda grass.
Research your weeds and learn what they tell you about your garden. Whether as indicators, food or soil improvers, weeds can be garden helpers, too.
Weed photo gallery list from UC IPM is here, a LIST OF ALL WEEDS. Find the common name to see a photo.
If you wish to ID the weed, use the UC IPM weed ID tool here:
The UC Master Gardeners of Napa County are volunteers who provide University of California research-based information on home gardening. To find out more about home gardening or upcoming programs, visit the Master Gardener website (napamg.ucanr.edu). Our office is temporarily closed but we are answering questions remotely and by email. Send your gardening questions to email@example.com or leave a phone message at 707-253-4143 and a Master Gardener will respond shortly.
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.