By Susanne von Rosenberg, UC Master Gardener of Napa County
Weeds can serve some useful purposes, but unless you're an unusual gardener, you probably still prefer to decide what gets to grow in your garden and what doesn't. The four basic weed control methods are prevention, removal, smothering and exhaustion. Most gardeners will need a combination of these methods to control their weeds.
Annual weeds (those that sprout from seed each year) are easier to control than perennial weeds (those that regrow each year from underground structures such as roots, tubers and underground stems). Perennial weeds can spread from their underground structures and by seed.
Prevention consists of all the activities that keep weeds from growing or spreading. The most important one by far is preventing weeds from setting seed. Some plants, such as wild oats, produce “only” about 250 seeds per plant. More ambitious weeds can produce over 200,000 seeds per plant.
It's also important to avoid promoting weed growth. Soil scientists estimate that there are 140 weed seeds per pound of surface soil in cropland (or 200 million per acre). Most weed seeds sprout from the top half-inch of soil. If you can avoid disturbing the soil, you can minimize the weed seeds you bring to the surface for germination.
Controlling drip irrigation is another weed prevention method. Only put water where you want plants to grow.
Mulch is effective in controlling annual weeds as long as it's thick enough. Mulches prevent light from reaching the weed seeds, so weeds can't grow. I prefer mulches from natural materials, such as wood chips and compost. Coarse mulches need to be three to six inches thick to keep out the light, and finer mulches such as sawdust and grass clippings need to be one to three inches thick.
Make sure that water can still reach your plants; mulches absorb some of the water. Certain quick-growing vegetable plants, such as squashes, beans and tomatoes, form a thick leaf cover that also helps to shade out weeds.
If you feel ambitious, you can kill many weed seeds through soil solarization. This process will take four to six during the hottest part of the year, so you will not be able to grow a summer garden in that area. To be effective, it needs to be done correctly. The UC Integrated Pest Management Program website has detailed information.
To avoid spreading weeds between different areas of your garden or between your garden and someone else's, clean your garden equipment, clothing and shoes. Finally, avoid importing seeds. While manure is great for your garden, make sure it's composted first. Horses and cattle can pass 20 percent of the viable seeds they eat. Composting can kill many of those seeds, but bird manure is usually a better choice.
As for removal, one effective approach is “water, wait, cultivate.” Ready your planting bed several weeks before you intend to plant, and then water it to encourage weed seeds to sprout. Hoe out the sprouts, keeping your hoe shallow to cut off the weeds just below the surface. Then repeat this process. This approach will remove about 95 percent of the weeds that would normally sprout. When you plant, disturb the soil as little as possible to avoid bringing new weed seeds to the surface. Keep hoeing or removing weeds by hand throughout the growing season. If you've applied mulch, it's usually easy to remove the relatively few weeds that sprout by hand.
Smothering weeds is simply another form of mulching known as sheet mulching. Cut back your weeds to six inches or less and cover the area with cardboard, overlapping the sheets by at least six inches. Apply mulch on top of the cardboard. The cardboard will break down in three to four months if you keep it moist, and it prevents annual weeds from returning.
Sheet mulching will also temporarily banish perennial weeds, but they may re-emerge after the cardboard has broken down. For me, sheet mulching is the fastest and easiest way to reclaim weedy areas.
To get rid of perennial weeds that are already established in your garden, you need to exhaust their food supply stored in their roots or other underground structures. Let them grow a bit, cut them back to below the ground surface, then let them grow a bit again. Don't let them grow a lot because that could allow them to store more food. This process may take several years to work. If you have widespread perennial weeds (for example, Bermuda grass), you can repeatedly mow them close to the ground.
You might have noticed that I did not mention herbicides. They are truly a last resort and are usually not needed in home gardens. If you are growing your ornamentals, food plants and turf correctly, they will outperform most weeds. If you do have to use herbicides, follow the label directions carefully and use the least amount possible. However you tackle your weeds, just remember: they may be tough, but you're a lot smarter.
UC IPM has more information about weeds for Napa county home gardeners. Start here:
http://ipm.ucanr.edu/PMG/PESTNOTES/pn7441.html
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 mastergardeners@countyofnapa.org or leave a phone message at 707-253-4143 and a Master Gardener will respond shortly.
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.
http://ipm.ucanr.edu/PMG/weeds_all.html
If you wish to ID the weed, use the UC IPM weed ID tool here:
http://ipm.ucanr.edu/PMG/weeds_intro.html
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 mastergardeners@countyofnapa.org or leave a phone message at 707-253-4143 and a Master Gardener will respond shortly.
By Rob Williams, U. C. Master Gardener of Napa County
With this season's deluge of wet weather, thoughts of a bountiful summer harvest might seem far away. However, the emergence of some buds in trees and slightly higher day and night temperatures serve as a gentle reminder that spring is imminent.
With this in mind, there are a few things you can do right now to help ensure a successful summer vegetable harvest. Good preparation, thoughtful cultivar selection and consideration for the overall ecology and health of your garden are the foundations of a productive outcome.
Draw up a simple garden plan to help organize your activities. Decide what you will plant and when so you can maximize space, rotate crops and insure your crops have enough time to complete their growth cycle before the next season.
Radishes, for example, grow quickly whereas autumn squash might need several warm months. A plan can also guide you in timely ordering of seeds and seed starting.
Consider, too, such things as construction or repair of raised beds and irrigation lines. Are your irrigation lines still viable after a season of limited or no use? Repairing or replacing them over the next few weeks can help insure your garden is in shape for summer.
Get weeds out now while they are easy to pull. Consider planting a cool-season cover crop such as fava beans or peas. These quick-growing legumes can displace weeds, add nitrogen to the soil and serve as a component in your crop-rotation scheme. As a bonus, they are edible. After you harvest the pods, chop the greens and use them as mulch to improve soil tilth. Their extensive root systems can help break up compacted or heavy soils so you don't have to till wet soil, which is definitely not a good idea.
What to plant? With Napa Valley's Mediterranean climate, many summer vegetables feel right at home in pretty much any part of the county. Tomatoes, peppers, squash and corn are favorites in many local gardens. Of course, you should take into account your particular microclimate—any shady or windy areas, for example.
Local nurseries have a good selection of vegetable seeds and starts, but also consult specialty catalogs for heirloom vegetables and new hybrids that look enticing. Many heirlooms have exceptional disease resistance, flavor and overall hardiness. What's more, you can save their seeds for next year's crop, thus reducing your gardening expenses and increasing the diversity of your harvest. Hybrids have to be started from new seed every year.
Finally, consider the overall ecology of your garden. What can you do to improve it? Adding compost now can help prepare the soil for your transplants. Earthworms and other soil microorganisms will get started on making your soil a better host for the upcoming guests.
And while your main focus might be vegetables, consider planting other plants as pollinators. Nasturtiums can add color to your garden and serve as a resource for pollinators. And their edible blossoms can add a peppery note to salads. Blooming herbs and sunflowers also attract pollinators, which will increase the bounty of your harvest. Birds appreciate these plantings, too, and help keep pest populations down so you don't have to resort to harmful pesticides.
We avid gardeners look forward to a bountiful summer harvest. With a bit of planning now, we increase our chances of success.
Workshop: U. C. Master Gardeners of Napa County will host a workshop on “Growing Summer Vegetables” on Saturday, March 11, from 9 a.m. to 11 a.m., at University of California Cooperative Extension, 1710 Soscol Avenue, Napa. Learn what the garden needs to successfully produce spring and summer vegetables from seeds and seedlings. The workshop will cover soil types and preparation, temperature essentials, watering, fertilizing and harvesting, with a dash of integrated pest management. Online registration (credit card only); Mail-in registration (check only or drop off cash payment).
Garden Forum: Join the U. C. Master Gardeners of Napa County at a forum for home gardeners on Sunday, March 12, from 11 am to 1 pm at Yountville Community Center, 6516 Washington Street, Yountville. Bring anyquestions about anything in the home garden. Questions about fertilizing, watering, planting, plant care, diseases and pests, tools and tool care or nursery purchases are welcome. Register with Yountville Parks & Recreation or contact 707-944-8712.
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.
At a landscape seminar I recently attended, weed eradication was discussed and tools demonstrated. One of the tools had a long handle with a narrow blade to help remove taproots, like those on dandelions. Someone in the audience piped up and said, “I grow dandelion plants as a cash crop.” My ears perked up at that pronouncement. I thought of dandelions as a scourge.
Sure enough,a little research enlightened me about the good side of this troublesome weed. The dandelion that grows in the Napa Valley (Taraxacumofficinale) is, in my opinion, a major problem in the garden. Thriving in just about any garden venue, dandelions have a taproot that is hard to remove permanently.
The dandelion has been used as a pot herb and medicinal plant since Roman times. The seeds were so valued that people carried them on the Mayflower to the New World. High in vitamins and minerals, the young leaves are eaten in salads; the mature blossoms scent dandelion wine; and the roots are brewed for a coffee substitute. The dried leaves can be steeped for a mild tea, and the dried roots are a mild diuretic. I remember, as a child, seeing my dad come in from the yard with fresh dandelion leaves for the salad. My mom was not amused.
I am sure that my fellow gardeners agree that these plants are persistent. Although the taproot does break up the soil and provide nutrients for other plants, I'm not ready to give it any encouragement yet.
I have worked and worked to remove dandelions from my lawn, positive that I had the entire root structure only to have this annoying plant re-emerge in a few weeks. Dandelions prefer moist areas in full sun but can survive in some shade and dry soil if they get established.
The plant grows pretty much year-round in California except in the coldest areas, where it lies in wait for warmer weather. The taproot, while usually only 6 to 8 inches long, can reach 10 to 15 feet. No wonder I have a problem getting it all.
The leaves grow in a rosette.They have no true stems. Leaves are usually two to four inches wide and about up to fourteen inches long. Some have smooth edges; others have a jagged, tooth-like appearance that explains the plant's name. Dandelion comes from “dent de lion,” which is French for lion's tooth.
As a child, I picked the flowers to make necklaces, and then blew on the seed balls to watch the puffs float on the wind. No wonder this plant is prevalent. The seed heads have up to 300 seeds, which can travel by wind, sometimes helped by the breath of children, for miles.
There are more than 60 dandelion species. Taraxacumofficinale has small leaves, so harvesting them is labor intensive. If you are thinking of selling your crop, that idea is probably a “no go.” The summer dandelion is more upright, with larger leaves that are easier to harvest. For the most part, the variety sold in grocery stores is a hybrid of the chicories‘San Pasquale' and ‘Catalogna'. Commercial dandelion farmers are required to control their seed in some manner. Can you imagine living downwind from a dandelion farm?
The most interesting species of dandelion by far is the Taraxacumkoki-saghyz, also known as TKS or Russian dandelion. This variety has greyish upright foliage and more natural latex than the others types. During World War II, rubber supplies were sorely depleted. The Swedish Seed Association conducted a dandelion breeding program to increase the latex content in the root. The new TKS produced four to five times more usable latex than the common dandelion.
The Swedish study had been back-burnered until recently, when automotive-industry researchers began investigating TKS as a source of rubber for tires. Other scientists are looking closely at the hypoallergenic properties of the latex from this species, and exploring whether it could be used as a source of ethanol.So as you wrestle with dandelions in your landscape, keep its positive attributes in mind. One gardener's weed is another person's dinner.
Workshop: Napa County Master Gardeners will conduct a workshop on “Habitat Gardens at Home or School” on Saturday, May 16, from 9:30 a.m. to 11:30 a.m., at Skyline Park, Martha Walker Garden, 2201 Imola Avenue, Napa. Participants will tour the Martha Walker Garden to discover the plants and garden elements that attract bees, birds and pollinators. Master Gardeners will explain the value of habitat corridors whether the garden is in a rural, urban, or school setting. Online registration (credit card only) Mail-in registration (cash or check only)
Master Gardeners are volunteers who help the University of California reach the gardening public with home gardening information. Napa County Master Gardeners ( http://ucanr.org/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.
In the past, I have inadvertently uprooted a desired plant. With a quickly drawn breath, I immediately replant it, only to have it usually die anyway. A weed, on the other hand, will almost always replant itself if I leave it on top of the soil with any root system remaining at all. More often than not, it revives itself and continues on as if nothing had happened.
It is the time of year when weeds begin to prevail. Although honestly, I find that weeds are opportunistic in any season. I spend many days puttering around my garden, hoe in hand, uprooting and removing weeds.
I actually do not begrudge the effort as any time spent outdoors, for me, is a plus. What I do resent is the time spent removing weeds rather than in more pleasant garden pursuits. The proliferation of weeds and their seeming ability to grow by the hour is at times daunting. If you do not destroy them as small seedlings they will mature within days and distribute their seeds with abandon.
One of the weeds prevalent in our area is bittercress, also known as hairy bittercress, less-seeded bittercress or, more aptly, as popweed. It is a particular nemesis of mine. Bittercress is extremely prolific and will mature in only six weeks.
What intrigues and frustrates me about bittercress is its seed distribution system. These weeds are well camouflaged in my garden, and if I do not find them before they scatter their seed, the battle is lost.
You can easily kill them by pinching them or by disturbing the root system. But if you allow bittercress to mature and then try to pull it up, you will be rewarded with a mouthful or face full of seeds. The plant can literally shoot seeds for yards in all directions. Given that each plant can produce hundreds of sticky seeds, you have reproduction heaven.
Bittercress are the bane of wholesale nurseries as the seeds travel so far and travel on pots, in the water and in the soil. It's a good practice to remove the top half-inch of soil from any nursery plant before introducing it into your garden.
The key to weed removal is to get it when it is small. But getting down on my hands and knees is becoming harder as I get older. So I look for ways to avoid that effort. Often just scuffing the seedlings with my foot works well. It may look like I'm doing a soft-shoe routine, but it is effective.
Recently I purchased a long-handled tool with a stirrup-shaped blade. The stirrup shape allows me to get under the plant and uproot it without disturbing the soil much. However, many weeds will re-root unless I banish them completely, so I carry a bucket with me and deposit the weeds there. This method does require some bending but that's preferable to getting on my knees. For the cracks in the driveway (there are more post-earthquake), I use a sharp stick. The stick works great on the straight lines but requires a little finessing in the acute corners.
Weed killers abound at hardware stores and nurseries. Glyphosate, sold under several brand names, has been used to kill weeds since its registration in 1974. It readily kills emerging weeds without affecting the soil or leaving a residue. Always read and follow herbicide instructions.
I have found glyphosate effective in my yard's gravel areas, where weed removal is a problem. It has worked well except during winter, when it seems to take forever for the plant to dry up. The sprayed weeds do eventually die, but they remain upright and yellow for quite awhile and are as unsightly as the healthy weeds. I have not found a better method for killing weeds in gravel areas other than getting down on my knees and pulling them out by hand.
For more information on weed eradication, consult the Napa County Master Gardener web site (address below).
Workshop: Napa County Master Gardeners will hold a workshop on “Propagation and Seed Starting” on Sunday, March 1, from 2 p.m. to 4 p.m., at Yountville Community Center in Yountville.Master Gardeners will discuss and demonstrate several types of propagation methods, including division, soft wood cuttings, grafting and seed starting. Learn about the tools and techniques that lead to successful propagation and have a hands-on experience. To register, contact the Parks and Recreation Department at 707-944-8712 or visit its 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://ucanr.org/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.