- Author: Help Desk Team
Note: This was originally published in the Contra Costa Times
Conquer weeds by understanding their life cycles
As a gardener in Contra Costa County, you know from observation that weeds have an immense capacity to produce seeds. In fact, the high reproductive output of weeds is astounding. Per plant, pigweed produces 117,400 seeds, mullein 223,200, lambsquarters 72,450, shepherd's purse 38,500, johnsongrass 80,000, curly dock 29,500, and wild mustard a mere 16,000 seeds.
Weed flowers can be small and inconspicuous, but, after flowering profusely over a period of several months, they produce a tremendous quantity of seeds. Black medic, kikuyugrass, and spotted catsear flower 5 to 7 months. Dandelions bloom 9 months out of the year and each flower produces thousands of wind-borne minutely barbed pappus-bearing seeds which can germinate year-round.
The sheer quantity of seeds ensures waves of seedlings. Yet, germination is discontinuous: it doesn't happen all at once. In gardens and in other disturbed areas, seeds are stored in the soil until shallow tillage brings them to the surface where conditions for germination are ideal.
Weed seeds persist in the soil below the germination zone and can be viable for a surprisingly long period of time. Mustard seeds thought to be 600 years old were excavated from a monastery garden in Denmark and 11 of them germinated. The longevity of field bindweed seeds is over 50 years. Lambsquarters seeds are viable for 20 to 50 years. Grass seeds tend to live an average of 3 to 10 years, whereas broadleaf weed seeds can be part of the soil seedbank for a much longer time
Life Cycle of Weeds:
Like other members of the plant kingdom, weeds are classified as annuals, biennials or perennials. The seeds of summer annuals germinate in the spring and mature plants generate seeds in summer and fall. Winter annuals sprout in the fall, live through the winter and produce seeds during the winter and spring. Biennial weeds spend their first year producing leaves before they flower and bear seed during their second and final year of life. Perennial weeds propagate by seeding but also vegetatively by means of creeping roots, rhizomes, taproots or bulbils. Weeds in their various stages of growth, flowering, seed production and dispersal are with us all year.
Weed Seed Dispersal:
Weed seed dispersal is varied and opportunistic. Though many mature weed seeds fall next to the parent plant, quantities of others are tumbled along or parachuted for miles by wind. Some burst out of capsules, landing 3 to 15 feet away. Others hitch a ride by attaching themselves to animal fur with burs or seed hooks. Many are digested by birds or livestock, transported by water or by the gardener's boots and tools. In their quest for territorial expansion, weeds use gardens as seed factory sites, as seed storage facilities and as launching pads for seed dispersal by gardeners.
Production of large quantities of seed, opportunistic seed dispersal, long- flowering periods, long seed viability, year-round seed production, and
discontinuous germination are successful strategies that weeds use to ensure their survival and expansion.
Managing Weed Seeds:
Weed seed management works best if you combine methods of control. Choose an irrigation system such as drip irrigation or microsprinklers so that only your plantings are watered. Be aware that cultivation brings weed seeds to the surface where they can germinate. Do not let weeds go to seed and replenish their weed seed reservoir in the soil. Reduce weed seed germination by eliminating their light source through use of a thick layer of mulch.
For More Information:
If you would like more information about identification of and controls for specific weeds, consult these University of California web sites:
https://wric.ucdavis.edu/
http://ipm.ucanr.edu/PMG/menu.weeds.html
http://ipm.ucanr.edu/PMG/PESTNOTES/pn7441.html
Help Desk of the UC Master Gardeners of Contra Costa County (CG)
- Author: Help Desk Team
Bermuda buttercup (Oxalis pes-caprae) has become a tenacious and frustrating weed throughout California. From November through April, bright yellow flowers on leafless stalks and green shamrock-like leaves pop up in many of our landscapes. While it was brought from South Africa as an ornamental plant, it escaped cultivation on its route to being a chronic nuisance. It competes with other plants and is very difficult to control.
Bermuda buttercup develops from underground bulbs that produce a single vertical stem. A loose rosette of leaves will appear at soil level after the first rain. Small, whitish bulblets develop on the stem, and new bulbs form underground. Each plant can produce about a dozen small bulbs each year that easily detach from the plant and will increase the plant's spread quickly.
A couple of our favorite vertebrate pests (gophers and voles) consider oxalis bulbs to be a yummy food source and can spread the bulbs to new locations as they carry them back to their underground dens.
The best way to control Bermuda buttercup is to prevent its introduction into your garden. Don't move soil or plants from an infested site to another location that is free of the weed. Unfortunately, for many of us, it's too late for that tactic. So, what can we do when faced with the cheery yellow flowers popping up throughout the landscape?
Hand pulling can provide control if the entire plant is removed, including the underground rhizome and bulb. It's difficult to find all the bulbs without sifting the soil very carefully. Repeatedly removing the tops of the plants will eventually deplete the bulb's resources, but it can take years to be successful. It's important to remove the tops of the plants before they flower and form new bulbs.
It is difficult to smother Bermuda buttercup with thick mulch or even weed block cloth because it is a strong plant. If cardboard covered with a thick layer of mulch is used to try to smother the weed, continued vigilance in monitoring and pulling new growth will be needed in subsequent years. In one garden, weed cloth was laid under a brick walkway. The following winter, Bermuda buttercup pushed its way up through the weed cloth between the bricks. This made removing the plants even more difficult because the plants were being held in place by the weed cloth.
Several herbicides will effectively kill the tops of the plants, but will not kill the bulbs, so regrowth will occur.
Whatever method you choose to combat a Bermuda buttercup invasion, you will need to be persistent and prepared to continue in subsequent years.
For more information about managing Bermuda buttercup, see this web page: https://ipm.ucanr.edu/PMG/PESTNOTES/pn7444.html
Help Desk of the UC Master Gardeners of Contra Costa County (SEH)
Advice for the Home Gardener from the Help Desk of the
UC Master Gardener Program of Contra Costa County
Dear Help Desk: I'm writing to try to figure out the best approach to “fixing” our front yard: 4 years ago we pulled up the lawn and laid down weed block and put redwood chips on top. The weeds still spring up, and this year has been particularly bad. The wood chip “lawn” has essentially been overtaken by weeds. We'd like to retain the wood chip “lawn” in this part of the yard. Do you have suggestions for a fix? Should we just pull up the weeds and add 6” more wood chips as has been suggested by a friend?
1) Removing all the weeds currently growing. This ideally would be done by hand weeding, but you may also consider the use of herbicides. Which herbicide would work best is going to depend on the specific weed. If you need help identifying specific weeds, you can use the link below and we can provide help as well.
2) You may then want to water the area, wait for the weeds to germinate and then remove them while they are small. Doing this repeatedly a few times will greatly reduce your weed population long term.
3) Once you have adequately prepared your site, you will want to install a weed barrier. Ideally you want to use something organic that will decay such as cardboard or burlap. However, you may also try landscape cloth again.
4) After applying your weed barrier you will want to cover the barrier with 1-5 inches of mulch. The amount of mulch needed depends on which barrier you select. Landscape fabric requires less mulch than organic barriers.
5) This will not prevent all weeds and will need ongoing management. You will want to continue to remove weeds as early as possible, ideally by hand weeding. As your mulch breaks down, it also creates an organic layer that is very amenable to weed growth. The mulch layer does need to be periodically refreshed.
The following references may be helpful as you revitalize your front yard. It is certainly understandable that you want just mulch and no plants in your front yard, but it may be worth considering that putting desired plants into your yard will also help decrease weeds by competing for resources (sun, water, nutrients). Once you have eliminated these weeds, you may want to consider putting in some succulents or low-water native plants which may reduce the maintenance you need to do long-term.
http://ipm.ucanr.edu/PMG/PESTNOTES/pn7441.html
http://sacmg.ucanr.edu/files/163135.pdf
http://ipm.ucanr.edu/PMG/weeds_intro.html
Best of luck with your lawn and let us know if we can help further.
Help Desk of the UC Master Gardener Program of Contra Costa County (SES)
| Don't miss our 2019 Great Tomato Plant Sale - Antioch 4/13. Click here for more information>>: http://ccmg.ucanr.edu/tomato/ |
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.
Advice for the Home Gardener from the Help Desk of the
UC Master Gardener Program of Contra Costa County
Client's Request: I've heard that I can use yellow corn meal to control weeds. Is this doable and will it hurt the soil?
Help Desk Response: Thank you for contacting the UC Master Gardener Program Help Desk with your question about cornmeal and weeds. I am going to assume that you mean corn meal gluten (CGM), a by-product of corn starch manufacturing that is marketed to home gardeners for pre-emergent control of weeds, especially in lawns. Yellow corn meal makes great polenta, but won't do much for weeds!
University of California research has not shown CGM to be an effective weed control strategy, but in a lawn, it may work because it is high in nitrogen and will feed the lawn, making it more dense, and likely crowding out weeds. Lawns already fed with high nitrogen fertilizers probably won't show any significant benefit from CGM.
CGM will have no effect on already-emerged weeds; it only suppresses some seeds' ability to sprout. It is sometimes used though where only organic herbicides are permitted, but its effectiveness is still questionable. It should not have adverse effects on soil. Because it is high in nitrogen, it could be beneficial if your soil is deficient in that nutrient.
Better weed control can be achieved by heavily mulching the area, which will prevent weed seeds from sprouting. At this time of the year, late winter, when many of our weeds have already come up, you can try hand-pulling or hoeing out the small weeds. They are always easiest to control when they are small. This link will give you great information from UC about weed management in the landscape: http://ipm.ucanr.edu/PMG/PESTNOTES/pn7441.html. The key to successfully reducing the weed problem in future years is to make sure none of this year's weeds go to seed.
Weeds in our gardens are frustrating and seem to be extra-abundant this year because of all the rain we've had. Good luck!
Help Desk of the UC Master Gardener Program of Contra Costa County (SEH)
Don't miss our 2017 Great Tomato Plant Sale:
http://ccmg.ucanr.edu/EdibleGardening/GreatTomatoPlantSale/
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/).
Advice for the Home Gardener from the Help Desk of the
UC Master Gardener Program of Contra Costa County
Client's Request: As we discussed on the phone this morning, I have recently installed extensive drought-resistant landscaping. I have also added wood chip mulch to prevent weeds. However, I'm concerned about how to maintain it weed-free as well as other areas in my garden. Our phone discussion covered many of the usual techniques to prevent weeds in this situation. You said that you would do some further review and possibly provide me with some more options.
UC MGCC Help Desk Response: Thank you for contacting the UC Master Gardener Program Help Desk with your questions about weed control in your new landscape.
The first option is to put down a weed fabric (not plastic) on the edges of your landscaping to control the small, sneaky weeds that appear where the wood mulch tends to be thin. Once the fabric is installed, you can cover it back up with your wood mulch. This will stop the weeds from coming up on the edges of your pathways.
Another option we didn't discuss is using a weed flamer. Flamers require no chemicals, and don't result in groundwater contamination or chemical residues on garden. One plus for weed flamers is that they are usually considered an organic gardening method. For effective weed control, you can use flamers in spring and early summer as annual and perennial weeds emerge. Killing larger, mature plants requires more heat, so save time and fuel by flaming weeds when they're still young and tender. This is a good option for larger areas that need treatment.
You can Google ‘weed flamer' for local and online suppliers as well as additional safety guidance. The idea of weed flamers isn't to burn the plants, but to quickly pass over to apply the right amount of heat to cause the water in the weed cells to boil, causing the plant to atrophy and die. Torch remaining weeds once every two to three weeks in ongoing applications or as needed until the next frost. Flaming kills annual weeds completely but does not completely eradicate the roots of perennial weeds.
If you do decide to use a flamer, be sure to keep a water supply handy, and do not get the flame near anything flammable, especially your dry wood mulch back, for safety purposes. To be safe, you may need to pull the mulch back before using the flamer or drench the mulch first with water.
Here is a link to more (and extensive) information on weed control in your garden:
http://www.ipm.ucdavis.edu/PMG/PESTNOTES/pn7441.html
Please don't hesitate to give us a call if you have additional questions!
Help Desk of the UC Master Gardener Program of Contra Costa County (SLH)
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/).
