Advice for the Home Gardener from the Help Desk of the
UC Master Gardener Program of Contra Costa County
Response from the MGCC's Help Desk: Thank you for contacting the UC Master Gardener Program Help Desk with your request for weed identification. We really appreciate the picture that you sent along too. It was very helpful.
From your picture, this appears to be a weedy mallow. There are two types of weedy mallow that are common in California, the common mallow (Malva neglecta) and little mallow (Malva parviflora). Both of these mallows are also known as cheeseweed.
Malva (mallow) species look very similar. Neglecta and parviflora can only be distinguished by comparing the flower petals and fruit shape. Flowers bloom nearly year-round. They are small, white to pale pink and about 2/5 of an inch in diameter. Flower clusters are found at the bases of leaf stalks. Neglecta petals are longer than parviflora petals and the fruit of neglecta are smooth while those of parviflora are wrinkled. The fruit for both is sometimes described as looking like a tiny wheel of cheese with wedge-shaped sections therefore giving them the common name of cheeseweed. Each wedge of the fruit contains one reddish brown kidney shaped seed.
These annuals begin growing from seed with the first rains in the fall and quickly develop a deep taproot that becomes woody and makes the plant difficult to remove by hand or even with tools (as you have found). Left alone, these plants will spread and can grow between 2 to 5 ft. tall.
- Mallows are best controlled mechanically by hoeing or pulling out young plants.
- Young mallow can also be killed by cutting them off at the crown but older plants may re-sprout from the crown.
- Solarization is not effective for mallow control nor is flaming.
- Insects do feed on mallows but there are none that are specialized for control of these weeds.
- There are no chemical controls available for home use that are effective for controlling mallows. Mallow is one of the few weeds that glyphosate (“RoundUp”) is ineffective in controlling.
- Cultural control can be done by planting competitive desirable plants in areas where mallow is a problem. The shade provided by these plants will reduce germination and growth of mallow seedlings.
- Mulches can also be effective. At least 3 inches of organic mulch, such as bark or wood chips, will make it difficult for the seedling to emerge and will screen out the amount of light that mallow requires to effectively sprout. It is important to maintain the needed depth otherwise, the seedlings can push through and become established again.
I'm including two links that have additional information:
http://ipm.ucanr.edu/PMG/PESTNOTES/pn74127.html
http://ipm.ucanr.edu/PMG/WEEDS/little_mallow.html
I hope this information is helpful to you. Please let us know if you have any questions.
Help Desk of the UC Master Gardener Program of Contra Costa County (JMA)
Note: UC Master Gardeners Program of Contra Costa's Help Desk is available almost year-round to answer your gardening questions. Except for a few holidays (e.g., last 2 weeks December), we're open every week, Monday through Thursday for walk-ins from 9:00 am to Noon at 2380 Bisso Lane, Concord, CA 94520. We can also be reached via telephone: (925) 608-6683, email: ccmg@ucanr.edu, or on the web at http://ccmg.ucanr.edu/Ask_Us/. MGCC Blogs can be found at http://ccmg.ucanr.edu/HortCoCo/ You can also subscribe to the Blog (//ucanr.edu/blogs/CCMGBlog/)
Help for the Home Gardener from the Help Desk of the
UC Master Gardener Program of Contra Costa County
Client: I need help identifying the alliums in my backyard garden. These alliums have been growing in the backyard for 20+ years on their own. I always thought they were leeks but after pulling one out the other day to examine it, I'm not sure what it is anymore. It smells like an onion but it doesn't have all of the layers. Thank you for your help!

The description of A. triquetum is:
• leaves are mid-green with a rib running up one side that makes them more rigid;
• spherical white bulbs that reproduce vegetatively by dividing;
• white flowers atop a triangular stem in April and May;
• the whole plant dies back after blooming and setting seed
You can compare the group of photos (right) of Allium triquetum to compare to yours.
However, what is a little confusing is that there are no flowers evident in your photos, and this makes me question the identification. If you could bring us a sample of your plants, we would be able to do a more positive identification. Or you could send us photos of the flowers and confirmation that your plants die back after flowering.
We look forward to hearing from you.
Help Desk of the Master Gardener Program of Contra Costa County (SEH)
Note: The UC Master Gardeners Program of Contra Costa's Help Desk is available year-round to answer your gardening questions. Except for a few holidays, we're open every week, Monday through Thursday for walk-ins from 9:00 am to Noon at 75 Santa Barbara Road, 2d Floor, Pleasant Hill, CA 94523. We can also be reached via telephone: (925) 646-6586, email: ccmg@ucanr.edu, or on the web at http://ccmg.ucanr.edu/Ask_Us/ MGCC Blogs can be found at http://ccmg.ucanr.edu/HortCoCo/ You can also subscribe to the Blog (http://ucanr.edu/blogs/CCMGBlog/).
/span>Advice from the Help Desk of the
UC Master Gardeners Program of Contra Costa
Client: This weed is growing in my lawn. Could you please tell me what it is and how do I eradicate and/or prevent it?
MGCC Help Desk: Thank you for bringing the weed sample from your lawn for identification and recommendations on its elimination and control.
Annual bluegrass loves damp, shady areas. You can reduce favorable conditions for this weed by watering deeply and infrequently. The weed's shallow roots will not be able to reach down to where the moisture is. Annual Bluegrass will also invade lawns where the soil has become compacted. You can reduce lawn compaction by aerating during non-sprouting periods. This will allow water to settle deeper in the soil away from the shallow-rooted weeds.
For more information on this weed and its control, please see the UC Davis publication, How to Manage Pests in Gardens and Landscapes - Annual Bluegrass at http://www.ipm.ucdavis.edu/PMG/PESTNOTES/pn7464.html.
Please let us know if you have any additional questions
Help Desk of the UC Master Gardener Program of Contra Costa County (VLT)
Note: The UC Master Gardeners Program of Contra Costa's Help Desk is available year-round to answer your gardening questions. Except for a few holidays, we're open every week, Monday through Thursday for walk-ins from 9:00 am to Noon at 75 Santa Barbara Road, 2d Floor, Pleasant Hill, CA 94523. We can also be reached via telephone: (925) 646-6586, email: ccmg@ucanr.edu, or on the web at http://ccmg.ucanr.edu/Ask_Us/ MGCC Blogs can be found at http://ccmg.ucanr.edu/HortCoCo/ You can also subscribe to the Blog (http://ucanr.edu/blogs/CCMGBlog/).
Garden Advice from the Help Desk of the
UC Master Gardener Program of Contra Costa
(minor correction October 31, 2016)
Client's Request: How can I get rid of oxalis in my yard? I pull it out and think I've got it all, but it just comes back with more gusto the following year. It's annoying, to say the least!
Homeowners and gardeners wishing to eradicate Bermuda buttercup face a tenacious, prolific weed which has devised many successful survival strategies. Each year, after the first seasonal rains, and sometimes before in a dry year, about a dozen ovoid bulbils develop along the length of the threadlike, underground rhizome. These readily detach from the rhizome to replenish the soil seed bank.
Another survival technique of Bermuda buttercup is that, after initial removal by hand, new plants will grow from broken off stem segments left in the soil. Several passes at hand weeding may be necessary to completely remove this new growth. Discouraging survival of Bermuda buttercup can usually be accomplished by gently pulling on the plant and removing all of it just as it is about to flower. By this time, the parent bulb energy reserves are exhausted. The parent bulb should be completely dried out and most young bulbils are too immature to survive disturbance.
Though prevention is the best control method, soil solarization can reduce the bulb population. To be effective, solarization using a clear plastic tarp treated with an ultraviolet light inhibitor must be in place for no less than 4 consecutive weeks during June, July, or August. The sun's rays will heat up the soil to temperatures that are lethal to Bermuda buttercup bulbs (and most everything else in the top several inches). Some researchers investigating approaches for controlling Bermuda buttercup also suggest covering it with stiff cardboard and applying a thick layer of mulch. The goal is to weaken the bulbs and deprive the plant of sunlight, causing an inability to photosynthesize and eventual death by starvation. Chemical control can affect the top growth but is ineffective in preventing bulb germination.
The lack of movement of water and air between compacted clay soil molecules promotes the survival of Bermuda buttercup bulbils. Adding nitrogenrich organic matter will loosen existing soil particles and benefit soil structure by increasing porosity and improving drainage.
While complete eradication is practically impossible to achieve, following strict noncontamination practices, mulching, solarizing, improving soil structure and drainage are all steps gardeners can take to create an environment unfavorable to the establishment and survival of Bermuda buttercup.
For further information on managing this pest, visit www.ipm.ucdavis.edu and download UC's free Pest Notes publication 7444 entitled “Creeping Woodsorrel and Bermuda Buttercup.” (http://www.ipm.ucdavis.edu/PMG/PESTNOTES/pn7444.html)
UC Master Gardener Program of Contra Costa's Help Desk (CG)
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This is an updated article authored by Chantal Guillemin, UC Master Gardener, and originally published in the March 19, 2011, Contra Costa Times. The HOrT COCO blog editor takes all responsibility for the above updated version.
A minor error was corrected Oct 31, 2016 to reflect, per the Pest Note above that woodsorrel can be a pest in nursery container-grown plants, while Bermuda buttercup isn't. See the Pest Note referenced abov for the specifics..
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Come to the UC MGCC Program's Great Tomato Plant Sale
Walnut Creek 4/2&9, Richmond 4/9, and Antioch 4/16
Click for locations and plant lists!
Dozens of heirloom tomatoes & vegetables chosen especially for Contra Costa
Note: The UC Master Gardeners Program of Contra Costa's Help Desk is available year-round to answer your gardening questions. Except for a few holidays, we're open every week, Monday through Thursday for walk-ins from 9:00 am to Noon at 75 Santa Barbara Road, 2d Floor, Pleasant Hill, CA 94523. We can also be reached via telephone: (925) 646-6586, email: ccmg@ucanr.edu, or on the web at http://ccmg.ucanr.edu/Ask_Us/ MGCC Blogs can be found at http://ccmg.ucanr.edu/HortCoCo/ You can also subscribe to the Blog (http://ucanr.edu/blogs/CCMGBlog/).
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Hairy Bittercress (Cardamine hirsuta)
I've become fascinated with this weed, at least so far. I've more-or-less got it under control in my garden. I really don't remember it from years ago, but it sure has been a pest the last 5 years or so. Not a native of California, it is now here for the foreseeable future… and beyond. I can't say it's the worst weed in the garden, but it sure requires attention to keep it under control. Especially these days when it will be competing for available water.
Hairy Wintercress
Because Hairy Bittercress thrives in moist conditions and disturbed soil, it is also a pest in nurseries, and can be brought home via plant purchases. If you think that's a problem for you, some cautious gardeners carefully remove the top inch or two of soil in the pots before planting. (If you do this, you should dispose of the scraped-off soil in your green can.)
If all else fails, Hairy Bittercress is a member of the mustard family and is edible, but you need to do your own research to find the right recipe to enjoy it (for an example, see http://www.eatingniagara.com/2013/04/weed-wednesday-make-that-hairy.html). To get ahead of its persistence in the garden, it's definitely worth patrolling your garden for this weed once or twice a week during the winter and spring. It's easy to hand pull when young. Once the seeds pop, you'll be fighting a much bigger crop next year and it's rare that herbicides would be considered appropriate for control in a home garden.
Another reason it's my “favorite” weed? I still remember a fellow student in our Master Gardener class relating how she had “convinced” her young son to help weed the spring garden and he was complaining about the weed seeds popping in his face. She answered him by telling him to go in the house and get his safety goggles on and keep on weeding… something you might be considering adding to your gardening tools if you let Hairy Bittercress (Cardamine hirsuta) go to flower and reseed.
Steve Morse
Contra Costa Master Gardener
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