The Coastal Gardener - February, 2005
The month of the weeds
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February is the month of weeds. They are everywhere, the rains set their long dormant seeds in motion and the lengthening days encourage them to take off quickly. We all work with weeds whether we garden or not and I am surprised to find out how little most people know about weeds and how they work. To beat a weed you have to think like a weed.
First, weeds are opportunists. They have the ability to germinate quickly and take advantage of changes in the landscape. Most weeds are looking for disturbed mineral soil recently exposed to sunlight. This makes your garden an ideal spot to try since it is often kept tilled and open, like spaces between vegetable rows. Weeds avoid undisturbed land covered with vegetation or layers of organic materials like forest duff. Cultivating to get rid of weeds actually gives them new habitat to exploit.
Second, weeds can run to seed quickly, faster than native plants, producing vast quantities of seed with specialized mechanisms to send seeds far and wide. Think of foxtails stuck in hiking socks or tiny thistle seeds with a downy "sail" to catch the wind. The dreaded genista shoots it's seeds out of the pod in little explosions set off by dry, hot weather. Erodiums give each seed a needle like awn that screws the seed into the ground like a drill.
So now that we are thinking like weeds, how to we stop them? Deny them their needs. Thick mulch covering bare soil keeps weed seeds from receiving light and air, choking them out. Intensive vegetable planting or groundcovers work the same way keeping weeds from reaching the sunlight. Deny weeds the mechanism to reproduce. Pull genista in bloom before seeds can ripen, which can still open even if the plant is pulled out. Many a good broom puller is defeated by seeds that simply fell off the dying plants back onto newly disturbed soil.
Then there are weed killers; a subject not to be taken lightly and often is. Herbicides are specialized chemicals that damage a weeds ability to grow and many are created to kill just certain types of weed. These are called selective herbicides created to kill either grassy plants (monocots) or leafy plants (dicots). A selective grass killer like Grass-B-Gone will only work on grassy plants, weed or not and will pass over other weeds like dandelions and thistles (both dicots). Anything touched by a herbicide will de damaged so be careful, always read the label before you grab a spray and use it according to directions. Weed killers work best if a plant is in full leaf, actively growing.
Some weed dos and don'ts:
*DON'T spray on windy or rainy days. NEVER spray weeds near running or open water; over-spray can kill fish and amphibians.
*DO spray each weed carefully and completely, thoroughly soaking the leaves.
*DON'T spray tree trunks, vines stems or exposed roots that will soak up the chemical and harm valuable ornamentals or natives.
*DON'T cut weeds down first; you need to have an actively growing plant with good leaf surface to soak up the chemical.
*DO give the killer time to do it's work which can take up to 2 weeks and do reply a spray quickly if the plants does not die completely the first time. Never let the weed gain its strength back.
*DO deal with weeds in the earliest stages as seedlings, not robust adults ready to seed.
*DO use weed killers ONLY as a last defense after manual removal has failed. Pulling the weed out of the ground and disposing of it is really the most effective option that gives it no chance of resprouting or seeding.
Lastly, a weed is really a plant out of place and we should be careful of introducing plants that have a reputation for self-sowing in coastal settings. Generally hybrids and named cultivars are less likely to become invasive than those that grow true from viable seed. Check with the California Native Plant Society and Cal Invasive Plant Council for info about invasive plants and what to avoid.
Must have plant of the month: Euryops virgineus 'Tara' Rounded evergreen shrub from South Africa smothered in bright yellow star-like flowers December to May. More fine textured, graceful and maintenance than the common Euryops. 'Tara' can be grown as a woody shrub (average lifespan about 3-4 years) or as a winter /spring annual.
Underappreciated plant of the month: Mahonia repens. Pointed holly-like leaves on spreading shrubs to 1 foot tall, native to north facing slopes from Baja to Oregon. Mahonias have sulfur yellow flower clusters on branch tips in winter followed by edible purple fruit. Deer and drought resistant. A tough groundcover for sun or shade; under pines and oaks, Mahonia is perfect for mass plantings.
Enjoy! Dave Egbert
