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:
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 firstname.lastname@example.org or leave a phone message at 707-253-4143 and a Master Gardener will respond shortly.
By Iris Craig, U. C. Master Gardener of Napa County
January is a month for setting intentions, and many of us set intentions for our gardens. For some of us, the big goal is to be more organized.
How can you improve the organization of your winter garden? One way is to keep a journal. Describe the weather, your maintenance, what you planted and when you harvested. Your journal can include a photo or drawing of the garden for each month. By keeping track of what is going on in your garden, you start to see patterns.
You can also schedule tasks so you complete them at the best time. In most areas of the country, winter is a time when gardens rest. In Napa County, a winter garden can be just as much fun to care for and as productive as in June. Plus, you can turn off the irrigation and allow rain to water the garden for you. Tasks that are best accomplished in winter include replacing your lawn, planting annual flowers for color, planting bare-root trees or shrubs, improving your soil and caring for fruit trees.
Good soil enables plant growth. To preserve your soil structure, refrain from walking on it or tilling it while it is wet.
We can affect climate change through our soil maintenance practices. Soil is an ecosystem itself. It can sequester carbon, making it a carbon reservoir. Over-tilling soil tends to deplete it of organic matter and reduce the ability of plants to absorb water.
To protect and improve your soil, and to sequester carbon, plant a cover crop. Cover crops reduce soil compaction and protect the soil from erosion. They improve soil structure, increase organic matter and fix nitrogen.
Common cover crops include fava beans and other legumes. Legumes add nitrogen, and nitrogen is the main plant nutrient commonly lacking in our soils.
Another good cover crop is lacy phacelia (Phacelia tanacetifolia). It is in the borage family, native to California and grows well. It attracts bees and blooms all winter. Cover crops compete with weeds, often choking them out. However, while the soil is damp, you can easily control weeds by hand.
Should you decide to remove a lawn, now is the ideal time. You can use the lasagna method. Instead of digging out sod, cover it with sheets of cardboard topped with soil and mulch. The rain and soil organisms will do the rest. Within three to four months, you will find rich soil in place of the lawn.
With planning, you can have blooming plants in your garden all year. Choose shrubs that blossom in winter and plant them as soon as the soil is dry enough to work. (It should be crumbly.) Flowers for winter bloom include primroses (Primula vulgarius), violas, Iceland poppies, pot marigolds (Calendula) and sweet William (Dianthus). All will bloom early and tend to last through the rainy season. You can plant them in a container or planter box if the soil is too wet.
If you plan for it in late summer, you can have a winter vegetable garden in Napa County. Suitable vegetables include bok choy, kale, mustard greens and Swiss chard, as well as broccoli and cauliflower. You can also plant root vegetables in early fall for winter harvest; consider beets, carrots, turnips, kohlrabi and radishes.
If you missed this window, begin planning your spring garden. You can start many leafy spring vegetables from seed now and transplant the seedlings into the garden in early to mid-March. Most root vegetables should be sown directly in planting beds.
If you have frost-sensitive plants, such as citrus trees, or want to get a head start on your spring vegetable garden, protect your garden from frost with burlap or floating row cover. Create a frame with plastic tubing to drape the fabric and prevent it from touching plants. Anchor the fabric to the ground to keep out snails and birds. Remove burlap every morning so the plants can receive sun during the day. You can leave floating row cover in place; it warms the soil on sunny days.
To get more organized in your garden, consult the Master Gardeners publication, “A Month-by-Month Guide to Gardening in Napa County.” It makes gardening recommendations for each month and includes a section where you can record important information. The publication is available for purchase in the Master Gardener office (address below).
Next workshop: “Flowers and Foliage for the House, growing Flowers for Bouquets” on Saturday, April 27, from 9:30 to 11:30 a.m., at the University of California Cooperative Extension, 1710 Soscol Avenue, Napa. For more details & online Registration go to http://napamg.ucanr.edu or call 707-253-4221
The UC Master Gardeners of Napa County are volunteers who provide UC research-based information on home gardening and answer your questions. To find out more about upcoming programs or to ask a garden question, visit the Master Gardener website (http://napamg.ucanr.edu) or call (707) 253-4221 between 9 a.m. and noon on Mondays, Wednesdays or Fridays.
West of St. Helena in Napa Valley sits a lovely garden surrounding a small house with a large porch and big picture window. I had an opportunity to speak with the owner, Glenn, about how this idyllic spot came to fruition.
Several years ago, Glenn and Anne purchased this home hoping to retire in the next few years. They saw the potential in an outdated but solidly built home in the perfect spot, along a country lane yet close to town.
They needed to renovate the house first, and then plan the garden. They launched their project by hiring a landscape and garden designer to help clarify their vision for the plot. Seven elements of good design guided their decisions. They needed to consider the function, site, hardscaping, microclimate, water management, plant selection and maintenance of their ideal home.
Function: The landscape designer asked questions to help determine which design would best support their interests and needs. Glenn and Anne were asked how they planned to use their garden. Did they plan to entertain? If so, where? Did they have any specific plants in mind?
The couple expressed a desire for an aesthetically pleasing garden that would also be water- efficient, sustainable, friendly to wildlife and care-free. In the front yard, which the public could see, they wanted an attractive landscape featuring plants with color, scent and texture. They also wanted to attract butterflies, bees and birds, and they wanted color in every season. The backyard was to be a place to contemplate, sit quietly, read a book and entertain.
Site: Since guests would park on the street, the home needed a walkway from the street to the front door. The couple parks their own vehicles in the driveway to the left of a house, so another walkway was needed from the front door to the driveway.
Hardscaping: When the project began, California was in the middle of a serious drought. To conserve rain water, a swale (a depression between slopes) and series of berms (an earthen embankment defining the swale) were added to the front garden to percolate moisture into the soil. A fountain was added for birds and butterflies and placed so that it can be seen from the front porch and window.
The backside of the house had several steps and levels. The homeowners decided to make the landscape two levels and use locally mined paving stones on the lower level to the creek edge. To protect the house from water, the paved area slants away from the house and toward the creek. Well-placed potted plants protect people from accidently moving to the edge of the creek.
Several trees were dug up. An olive tree was removed and given away. Two crepe myrtles were moved from the backyard to the front.
Microclimate: The front of the house faces south; the back faces north. With a southern exposure, the front tends to be hot in summer, making it a good site for plants that flourish with little water. The trees and boxwood hedges on both the east and west sides of the front garden create several microclimates requiring differing kinds of plants.
With its northern exposure, the backyard is cool and moist, with little variation in climate. It is ideal for water-loving plants.
Water management: Once the two levels were defined in the backyard, the grass was removed using the sheet-mulching method. In the fall, a plan for watering was devised. The design relies in two drip systems. The main pipes for the back were placed under the paving stones. Glenn chose a meter that he manually adjusts himself according to variations in rainfall and temperature.
Plant selection: As you enter the front walkway, the scent of night-blooming jasmine (Nyctanthes arbor-tristis), English lavender (Lavandula angustifolia) and mock orange (Philadelphus) greet you. At the base of the porch steps, pots of gardenia (Gardenia jasminoides), one on each side, add to the scent. Sun-loving California fuchsia (Epilodium) andmanzanita (Arctostaphylos spp) are among the plants that grow atop the berms that define the natural stone swale meandering through the garden. Both attract butterflies, hummingbirds and bees.
Below the boxwood (Buxus) are newly planted red-twig dogwoods (Cornus sericiae). In the corner below the porch is Anne's “conversation corner” shaded by the bloodgood Japanese maple (Acer palmatum). Other plants for the back garden include a fragrant flowering currant (Ribes sanguineum ‘White Icicle'), dwarf hydrangea (Hydrangea paniculata ‘Bobo') and prostrate rosemary covering the creek bank.
Maintenance: Anne and Glenn can keep up the garden themselves due to the low-maintenance design. When they need help for tasks like transplanting trees, they hire local people.
For an opportunity to be inspired and learn more, you can visit Glenn and Anne's' garden on Sunday, May 21. It is one of six Master Gardener-owned gardens featured on the U. C. Master Gardeners of Napa County's “Discover Garden Magic” tour. Purchase tickets online at
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.
The process I use is called sheet composting, and it is simply a method of building a compost pile in place. You can not only use this procedure on well-turned vegetable beds but also on a lawn, or part of a lawn, that you would like to use differently.
I gather materials for sheet composting throughout the year so that by fall I have a big pile of clean cardboard. I avoid the type of cardboard with slick sides because it takes longer to break down and contains clay. I also gather dried leaves, newsprint, decaying plants without seeds, some compost and aged chicken manure. In short, I use the same materials you would use in a compost or worm bin.
If you plan to sheet compost in an area that has never been dug, then turn the soil to a depth of two feet. This process aerates the soil so air and water will move through it more easily. If you are sheet composting in a grassy area, then loosen and turn the sod over so it will die. You will build your pile on top.
If I have old vegetable plants still in the beds, I cut them up and leave them in place. I may also put some kitchen waste on top of that. Then I build alternating layers, as if making lasagne. You can use whatever organic materials you have. I usually use cardboard, leaves and newsprint (laying them out in sheets – no need to cut up) or shredded paper. Then I repeat the layers. I top off the pile with aged compost and chicken manure. If my garden plot has diminished in height during the growing season, I may add more clean soil or compost when I construct the layers. I moisten each layer, then wet everything again. Then I cover with a plastic tarp, making sure it is secured on the sides so it does not go flying in the wind.
Watering each level is important because it encourages the microbes and other creatures to wake up and go to work. The red wigglers used in worm composting will start to move in and munch on the foods they love. They especially like cardboard and will move inside the corrugation. They enjoy the glue that keeps the cardboard together, and I often find that the cardboard layer disappears first.
Depending on the rain, you may not have to water the pile during the winter. However, it is a good idea to check the pile from time to time and water again if necessary to keep the layers moist.
In late April or early May, remove the plastic and see what has happened to your compost pile. It should be full of red wigglers and other creatures, and you may see some little white bugs hopping around. These creatures worked the pile for you, so you don’t have to do spring digging. As they worked through the compost, they turned the soil for you.
Sometimes the cardboard or other items are not completely decomposed by spring. I plant in the bed anyway by cutting holes in the cardboard where I want my plants to grow. On other occasions, I have covered the soil with cardboard and cut holes for my plants. This cardboard layer helps conserve soil moisture.
I once sheet-composted a bed in July and covered it with plastic. In late September I removed the plastic and found no trace of the materials I had layered just a few weeks before—only a bed of wonderful soil.
The droppings that the worms leave behind (known as worm castings) are beneficial to plants. They are a mild natural fertilizer containing all the trace elements. Some call these castings “worm gold.” It sells for about $600 a yard. When I plant in the spring, I do dig in some more chicken manure and worm compost from my worm bins.
Napa County Master Gardeners welcome the public to visit their demonstration garden at Connolly Ranch on Thursday mornings, from 10:30 a.m. until noon, except the last Thursday of the month. Connolly Ranch is at 3141 Browns Valley Road at Thompson Avenue in Napa. Enter on Thompson Avenue.
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.