By Susanne von Rosenberg, UC Master Gardener of Napa County
One thing that Master Gardeners talk about a lot is putting the right plant in the right place. That means choosing plants adapted to the climate, to the soil in your garden and to the amount of sunlight and water they will receive.
One other consideration is whether the plants you're considering are invasive. Invasive plants threaten our wildlands, outcompete native plants and change the habitat so it is no longer suitable for some native species.
As a result, invasive plants pose a substantial threat to endangered species. Invasive plants can also threaten agricultural lands by crowding out crops and rangeland forage. Some are toxic to livestock or wildlife.
According to the California Invasive Plant Council, invasive weeds in pastures and farmland cost an estimated $33 billion per year nationwide. California alone spends an average of $82 million per year to deal with invasive plants.
Even in the suburbs, invasive plants can cause problems. Pampas grass and Scotch broom increase fire fuel loads; other invasive plants can clog creeks and increase the risk of floods. Still others consume large amounts of water that would otherwise have gone to other plants, waterways or drinking water.
Until I became a Master Gardener, it never occurred to me that garden centers and nurseries might sell problematic plants. Unfortunately, many of the plants causing problems in California were introduced through the horticultural trade. We need to educate ourselves to make sure that we don't plant a future problem.
I've been surprised how often a plant that seems otherwise ideal for my garden turns out to be potentially invasive. Gardening catalogs are another source of invasive plants. Some of these plants may be perfectly harmless in other parts of the country but invasive here.
How can you know if a plant you're considering might be invasive? First, you can check the Calflora website, which provides information on a large number of plants grown in California, including whether a given plant is considered invasive or has invasive potential.
You can also consult the California Invasive Plant Council website, which has an alphabetic list of problematic plants. That list includes plants commonly sold through the horticultural trade and assigns a rating of high, medium or low risk of invasiveness. In addition, IPC maintains a watch list of plants that aren't currently invasive in California but risk becoming so.
As you evaluate a plant for invasive potential, consider these questions:
Is the plant known to be invasive in other locations with a Mediterranean climate?
How readily does the plant reproduce? On average, how many seeds does it produce each year, and how easily does it germinate from seed? How long will it take until the plant is mature enough to set seed?
Does the plant spread vegetatively, such as via underground running stems (like running bamboo)? Can a new plant sprout from small pieces of root, like bindweed does?
How tough is the plant? Does it need regular water or special growing conditions to germinate?
Could the plant hybridize with existing plants?
Are other species of the same genus, or a related genus, invasive in a similar climate?
Would the plant increase the risk of fire? Is it highly flammable or does it soak up a lot of water and leave surrounding vegetation dry?
How easily can animals, wind or water spread the plant's seeds or vegetative matter?
How hard is the plant to remove or control?
Unfortunately, many of the qualities that make a plant desirable may also predispose it to being invasive. If it is adapted to our climate, easy to grow and requires little water, it meets some of the criteria of a potentially invasive plant.
Compared to well-behaved plants, invasives reproduce more readily, crowd out desirable plants and may be difficult to remove. So if a plant's description says that it “reseeds readily” or “spreads easily,” think twice. If it “grows rapidly” or is “adapted to adverse growing conditions,” do some follow-up research.
Unless you know the plant, it it's a good idea to spend a few minutes online to reassure yourself that the plant is well mannered. Don't rely on old information. Some plants have been designated invasive only recently, and new plants are added to the list regularly.
Food Growing Forum: Napa CountyMaster Gardeners will present a discussion of “Cane Berries” on Sunday, November 14, from 3 p.m. to 4 p.m., via Zoom. Register here to receive the Zoom link.
Got Garden Questions? Contact our Help Desk. The team is working remotely so please submit your questions through our diagnosis form, sending any photos to firstname.lastname@example.org or leave a detailed message at 707- 253-4143. A Master Gardener will get back to you by phone or email. For more information visit http://napamg.ucanr.edu or find us on Facebook or Instagram, UC Master Gardeners of Napa County.
by Penny Pawl, U.C. Master Gardener of Napa County
Oh no, I've done it again. I have fallen in love with a plant and its beautiful flowers. I planted it; it grew well and then I discovered that it is on the invasive plant list. What to do? And why is this plant on the list?
Many of the wonderful plants that I have planted over the years are on this list. How do authorities create this list? Some of those plants include pampas grass (Cortaderia jubata), mullein (Verbascum),butterfly bush (Buddleia davidii), Watsonia and privet (Ligustrum spp).
Most gardeners are aware that bamboo is invasive. Years ago, my husband and I planted bamboo in a wine barrel. Because we knew it had a spreading habit, we set the barrel on cement blocks. A few months later we noticed that a stem had come out the bottom of the barrel and was inching its way across the soil toward our house. Bye bye, bamboo.
Scotch broom (Sarothamnus scoparius) is probably the most notorious problem plant. It has taken over entire areas of our state and moved up the coast into Washington. It is also a problem in many other states. I have read about groups going out to remove this plant from parks and other wild areas.
Scotch broom spreads by the root system. The roots have nitrogen-fixing bacteria so the plant grows all year. It also produces large amounts of seed. If left alone, it will take over and crowd out native plants.
Pride of Madeira (Echium candicans) is native to the island of Madeira. I visited there a few years ago, saw the plant and fell in love with its tall purple spires. I planted one about two years ago. It has grown well and has not needed water or care. It bloomed this year, and the bees and other pollinators were in heaven.
Before I planted more, I decided to check its status. Alas, it is also on the California list of invasive plants. Each one of those little purple flowers produces lots of seeds which take root easily in our soils.
I do not plan to remove it, so I went out one evening as the flowers faded and before the seeds set, and cut it back. I did it at that time of day to avoid the bees and other insects. I will need to repeat this every year to keep pride of Madeira from becoming a pest in my garden and my neighbors' gardens.
A couple of years ago I snipped two pieces of honeysuckle (Lonicera) and rooted them. They are now in barrels growing up a big trellis. When I looked for more information on this plant, which is currently in full bloom, I discovered it, too, was considered invasive. Like pride of Madeira, it produces many seeds and pollinators love it. I have to trim it after flowering to keep the seeds from spreading. It also spreads when long runners touch the ground and take root.
The California Invasive Plant Council (Cal-IPC) list has been around for many years. If you are serious about preventing the spread of invasives, you should check the list before planting. You can find it on the Cal-IPC website along with photos to help with the identification.
Some of the plants in the weed category came in with New World settlers. The weeds were hitchhikers. Others such as Scotch broom were brought in because they grew so well in their native areas.
What do these plants all have in common? They are generally drought tolerant, and they produce massive amounts of seed. Birds love the seeds and spread them far and wide. Some invasive plants, such as wisteria, spread when their branches touch the ground and take root, or their root system moves around seeking water. When I trim the flowers of invasive plants, I don't put them in my compost. I put them in my brown yard-waste bin so they can be hot-composted by the city.
If, like me, you have a beautiful invasive plant growing in your garden, take care to keep it from taking over the whole garden. Otherwise, be safe and replace it with a native plant instead.
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./span>
Pat Hitchcock, U.C. Master Gardener of Napa County
Weeds aren't the only troublesome invaders in many Napa Valley gardens. Several other plants, not usually thought of as weeds, can be equally problematic. These thugs are the larger plants, shrubs and trees that, if left undisturbed, can spread into native habitat and crowd out native species.
Cotoneaster is a shrub in the Rosaceae family that grows enthusiastically in my neighborhood. The New Sunset Western Garden Book describes its growth habit as fountain-like with “graceful, arching branches.” Its summer sprays of small white flowers become red-orange berries in fall. Robins, cedar waxwings and other birds love them.
While cotoneaster is native to Eurasia, most of the cultivated varieties originated in China. They were introduced in California before 1900 but have only been reported as invasive in the last 20 years or so. With help from birds, they self-seed abundantly and can supplant native toyon (Heteromeles arbutifolia) in natural areas.
Another problem plant is the Himalayan blackberry or Armenian blackberry (Rubus armeniacus). Native to Armenia and Northern Iran, this plant was introduced to North America in 1885 as a fruit crop. It soon escaped into the wild and is considered invasive throughout temperate climates. While the berries are delicious, the plant is thorny and rambunctious. Canes can grow 30 feet long.
The plant propagates not only by seeds but also by “tip rooting” when the tip of the cane touches the ground and forms roots. If you ignore this plant for long, it creates a dense tangle of old brown growth and wicked, thorny green canes. It likes to grow among other shrubby plants, including the climbing roses and butterfly bushes (Buddleja) that screen my front bedroom windows from the street. Removing the blackberry vines that wander into that bed requires protective clothing as well as sharp pruners and a sturdy digging tool for prying out roots.
While the cotoneasters and blackberries probably invaded my property, another troublemaker—privet—was planted intentionally as a hedge. Three species of privet (Ligustrum spp.) are on the
California Invasive Plant Council's watch list, which means they have not yet been rated invasive in the state but are raising concerns. Those three are glossy privet, Japanese privet and California privet. Glossy privet (Ligustrum lucidum) is likely the one growing (and spreading) in my yard.
If kept trimmed, glossy privet makes a dense hedge. However, if left unclipped, it will reach tree height, bloom heavily in spring and produce a large crop of small black berries. The falling fruit can stain pavement and make a mess on parked cars. Birds attracted to the berries contribute to the mess and help spread the seeds, so new plants volunteer everywhere. After the fruit is gone, the fruiting clusters are unattractive. Sunset advises readers to consider the disadvantages of privet before planting it. I wish whoever planted it on my property had done so.
My property also has an abundant supply of ivy (Hedera helix, H.canariensis). Ivies are native to Eurasia and northern Africa but are now widespread. The California Invasive Plant Council lists ivy as being high in impact, invasiveness and distribution. I try not to let it climb into trees, and I pull it off the north side of the house, where it seems to like the micro climate. It infiltrated the overgrown hedges along the street and provided some screening where it grew densely on an old wire fence. I didn't think anything could kill ivy, although, after five years of drought, a small section in front of my house spontaneously died.
Once I was answering calls at the Master Gardener Help Desk when a client called to ask if we could help him figure out why his ivy had died. After doing some research, I was still stumped; this is a plant that does not succumb to pests or disease. I consulted a U.C. farm advisor specializing in weed science, and now we would both like to know why that ivy died. Finding an efficient way to control ivy in our forests and riparian areas would be a wonderful discovery. Meanwhile, in my yard, I whack it back from time to time in an effort to keep it from taking over.
All of these plants were brought to California intentionally because they had characteristics that seemed useful or attractive. Some of them are still sold in nurseries. But in our state's hospitable climate, the plants have escaped cultivation to become nuisances in wild areas as well as in some gardens.
For more information about invasive plants, check out the California Invasive Plant Council's website, CAL-IPC. The lesson here is to consider the unintended consequences of the things we do. After researching weeds for the past few weeks, I am vowing to be careful about the new plants I introduce into my garden.
Workshop: U. C. Master Gardeners of Napa County will conduct a workshop on “Rose Pruning and More” on Sunday, January 22, from 1 p.m. to 3 p.m., at the Yountville Community Center, 6516 Washington Street, Yountville. Learn 10 important facts about roses, rose pruning and rose care and maintenance. Registration is $12 per person, free to Yountville residents. Register with Yountville Parks & Recreation or call 707-944-8712.
Workshop: The Integrated Grape Team from the U. C. Master Gardeners of Napa County will host a workshop on “Home Vineyard 1” on Sunday, February 5, from 12:30 p.m. to 4:30 p.m., at White Rock Vineyards, 1115 Loma Vista Drive, Napa. Learn what to do, what to look for and what to plan for in the vineyard between February and August. This is an outdoor lecture so dress accordingly. Registration is $5 per person.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.
There have been many times that I have considered purchasing a machete. What better way to eradicate gardening blunders, and in such a flamboyant manner? I make many of my mistakes through ignorance and often from just not reading instructions.
I own two plants that might not be considered invasive plants, but they definitely have invaded my garden and most assuredly are mistakes. They are Potentilla and morning glory.
More than 20 years ago, when I was just starting out in the gardening game, I was looking to do something in my side yard. The space runs the full length of the house—about 45 feet—and is about 7 feet wide. I was looking for an easy fix that required little or no maintenance but would be pleasant to look at.
My husband and I were in the midst of raising three kids and working 40 hours a week, after all. Being an inexperienced gardener, I did not realize that the traits I sought are rarely found together.My research turned up a groundcover called Potentilla. With its deep green ground-hugging foliage, cute yellow flowers and low water requirements, what's not to love? I ordered several flats and proceeded to plant the Potentilla in the side yard.
Had I done more research and asked around, I would have found out Potentilla's true nature and perhaps decided against it. I can only imagine that the person responsible for naming this plant did so with tongue in cheek. I mean, it is truly “potent.”Virtually impossible to assassinate.
Potentilla is now growing throughout my entire yard:popping up in the lawn, in all the garden beds, around the copping on the pool, everywhere. Every year it gets a rust fungus that is hard to eliminate. Part of each time segment I spend in the garden is dedicated to Potentilla patrol. I see no end in sight. It must be said, though, that the side yard looks great.
You would think that I would have learned my lesson and not committed a similar error again. In my defense, perhaps my head was so swollen with pride at my recent graduation from the University of California's Master Gardener program that I wasn't thinking clearly. When I received a congratulatory card with morning glory seeds enclosed, I lost my mind and planted them. This packet of seeds turned intothe gift that keeps on giving.“Big mistake” hardly describes the situation.
True, the morning glory flowers are fun and beautiful to look at. The phrase “a riot of color” comes to mind. They bloom in the morning, as their name suggests, and are largely closed by noon. A small seedling becomes avine that clambers up and over virtually any obstacle to create a carpet of color.
So what's the problem? First, because they are annuals, they die back in cold weather and go to seed. So now your landscape is festooned with yards of spent vines. I learned the hard way that you need to pull the vines down before they go to seed. If you wait until the vines are dry and the seeds are falling or ready to fall, pulling the vines down unleashes a shower of seeds.
The propagation potential is frightful enough, but to add insult to injury, the seeds are poisonous. Birds, normally nature's little vacuum cleaners, will not touch them. The seeds also endanger people and pets. The toxicity is mild to moderate but common effects include diarrhea, anemia, uncoordinated movements and liver failure, depending on how much was ingested.
So now I not only have to remove the vines but I practically have to use tweezers to pick up all the seeds. Any seeds that I miss will grow into a plant in the spring, repeating the entire cycle. Maybe morning glory is lovely in the wild.In my yard, not so much.
The moral to the story is, research a plant's characteristics and growth patterns before planting it. Ask at local nurseries, consult your neighbors and look online. The Napa County Master Gardeners staff a help desk to give advice and planting information. Check our website (address below). Avail yourself of these resources before you, too, find yourself on Potentilla patrol.
Tomato Sale and Education Event: Napa County Master Gardeners are hosting their third annual Tomato Sale on Saturday, April 18. Join us in the South Oxbow parking lot in Napa, 9 a.m. until sold out. We have a bountiful selection of strong, young plants: heirlooms, hybrids, cherry, paste and just plain good eating tomatoes of all sizes. Remember to bring your own box to safely transport your plants home. Click on the link above to read descriptions of the varieties for sale.
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, 1710Soscol 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
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.