What about weeds?
From California Natives Wiki
There will always be weeds. The wind is the key way that weed seed find their way into your yard. And all sorts of critters carry and drop seeds in their travels through the urban wilderness. Your soil also "banks" seeds. When plants drop their seeds, many can remain dormant for years until the right conditions cause them to germinate. With weedy plants sending their seeds into your yard, it is important to be vigilant and employ different strategies to keep them under control.
The main question is whether you let weeds bully your garden or you bully them. The fact of the matter is that the more you weed, the less you'll have to weed. When you diligently remove these unwanted plants, especially before they set seed, you'll gradually and effectively reduce the number of weeds that germinate in your garden.
Diligence is the key. Spend a certain period in your yard every day or every week to remove weeds. As you spend this time in your garden through the year, you'll learn their life cycles and you'll be better prepared to attack them in the appropriate manner and at the appropriate time. They are plants, after all, and have certain characteristics that you can learn and use to their dis-advantage. You'll learn when certain weedy grasses germinate, that some have deep taproots that need to be pulled up as well, that some are evil geniuses that have developed incredible survival techniques, and that some are actually push-overs...you just need to hit them before they seed.
Remember the old adage, "One year's seeds equal seven year's weeds."
Minimize Soil Disturbance
Your first strategy is to minimize soil disturbance in your yard. Any time you dig around your soil, you will expose seeds to the surface. You'll often find new weeds germinating in areas where you have recently planted, weeded, or otherwise moved a little dirt around. Many weedy plants are very effective at colonizing these disturbed areas. When you move or disturb any soil in your yard, watch those areas more vigilantly the first year or two.
The Bradley Method
The Bradley sisters developed a habitat restoration process in Australia to combat weeds. As they hiked along wildland trails, the sisters would pull invasive weeds. Over time, they discovered that invasive species were reduced in number. You can employ this same process in your yard. As you walk through your yard each day, pull a few weeds. Make sure you focus on those that are flowering or about to go to seed. Another approach is to pick a starting point in your yard and every day for just 15 minutes or once a week for half an hour start pulling weeds from that point. You'll eventually work your way through your yard, clearing weeds as you go.
In southern California, its always weed season. But different species appear at different times of the year. Poa annua will start popping up in late Fall and be finished by Spring, while various Chamaesyce species germinate easily with warmer temperatures and spend the Summer spreading across pathways and disturbed areas. Learn which weeds appear during which season, and adjust your strategies based on their specific life cycles.
Should I Use Herbicides?
There is great debate about using herbicides such as Roundup. Many people are uncomfortable using poisons in the garden, especially when children and pets are around. This can be the fastest way to eliminate problem weeds, particularly in a large area.
Common Weeds in Southern California
Here are several common weeds that you should know:
- Ehrharta erecta: This weedy grass is an import from South Africa. It germinates most readily in Fall when the weather cools and rains begin. It can grow fast, survives summer drought, and loves garden conditions that provide additional water. The California Invasive Plant Council (Cal-IPC) lists E. erecta as a plant that cause serious problems in native ecosystems. Virtually all E. erecta seeds will germinate, so it is critical to pull these plants before the seeds drop. Better still to pull them before they flower. This grass will easily bully its way into your yard and crowd out other plants.
- Oxalis pes-capra: Many are charmed by this diabolical invader...until they try to contain it. O. pes-capra is endangered in its native South Africa, but is rampant throughout California. It forms small bulbs deep in the ground and sends out fleshy stems and roots in Fall when the weather cools and rain begins to fall. By Spring, cheery yellow flowers are massed over a clump of clover-like foliage. But it can spread. Those roots form multiple new bulbs during the growing season, resulting in an exponential growth unless contained. And containment is difficult. Pulling leaves behind root segments that can form new bulbs. Herbicides tend to slow it down, but don't outright kill it. Diligent, steady, constant attention is needed to get these under control. Schedule at least one day per week when you will pull or dig O. pes-capra, and do so with strict regularity.