General Weed Control
Prevention is by far the best weed control. Avoid carrying seed on clothing, shoes, automobile tires or pets. Check potted plants for any weed seedlings. Diligent attention to the spread of weeds can save a lot of extra effort later. That being said, weeds do have effective dispersal methods that allow them to spread. Avoiding creating conditions that favor weed seed is also important.
Bare, sunny soil is ideal for weeds. Whenever possible avoid clearing ground completely. This is particularly important when thinning vegetation for fire prevention. Thinning should be limited to 50% cover to minimize weedy, flashy fuel, that will only increase fire risk.
What is 50% cover? Picture an orchard with staggered rows of trees. This is a model for what you want with native bushes. Looking straight down from above half of what you would see is foliage and half dirt. This provides spaces where embers can settle out while limiting fire spread from plant to plant when one ignites.
What can be done if you already have weeds? This often depends on the type of weeds you may have. While this can be very specific, there are techniques that generally apply.
Annual weeds are those that live their entire life cycle from germination to mature seed production in one year or season. These plants tend to have relatively shallow roots and often will not regrow from roots. These can often be controlled by hand pulling or hoeing prior to flowering. After flowering they can still be pulled but the flowers and any seeds should be bagged and discarded.
Biennials have a two-year life cycle, generally staying small, often in a rosette, the first year before blooming in the second. Often they have a tap root that may be pulled. These can be treated like annuals. Repeated removal of the flower stalk can be effective. Sometimes, especially when the ground is hard and there is no time for repeated weeding, they may need to be controlled with herbicide.
Perennials are plants that live for more than two years. They often reach maturity and produce seed over several seasons. Often they have extensive root systems that are difficult to pull. Herbicides are often the best way to control these weeds. However, perennial seedlings can be dealt with like annuals.
What if I have a bare yard that I want to plant? In this case it is more effective to rid the yard of weed seed. Using a per-emergent herbicide is one approach which can work if you are planting. 'Water Up Weeds' is another alternative. This involves watering the sight to stimulate seed germination. These seedlings can then be removed before they produce new seed. Rake the soil to expose yet more seed and water again. This will germinate more plants that can be removed. Keep repeating until not more weeds grow. The weed soil seed bank will be depleted and you can plant or sow seed.
A word about herbicides…while herbicides can be an effective tool for controlling weeds, they do pose a potential hazard to people and the environment. Read, understand and follow all label directions. If in doubt, ask. The County Ag Department/UC Cooperative Extension is a resource that has the most up to date information and can provide options and alternatives for your situation. This resource can also help identify your plants: http://www.sandiegocounty.gov/content/sdc/fha/location.html