Spring brings out the best and the worst in the garden. While warm season annuals and vegetables are getting established, so are a variety of weeds. Just like other annuals and perennials, they respond to the changing weather. Cool weather and moisture stratified their seed through winter. Warming moist soil prompts germination. Warm and sunny spring weather promts rapid growth.
There are all sorts of weeds. A few are big trees like bluegum eucalyptus and shamel ash. Some are substantial shrubbery, like privet and cotoneaster. Pampas grass and giant reed are big grassy perennials. The most familiar and prolific weeds are annuals or small perennials, like foxtail, burrclover, purslane, bindweed, sowthistle, pimpernel, spurge, crabgrass and Bermudagrass.
It is best to pull weeds as soon as they are big enough to grab onto. It will take more effort to pull them as they disperse their roots, and as the soil gets drier through spring. Unwanted shrubbery and tree weeds should be pulled like any other weed because they are likely to regenerate from roots if merely cut down. Once they recover and grow more, they will be much more difficult to pull.
Many small grassy weeds can be cut down low with a weed whacker, instead of pulled out completely. In some situations, low cut or mown weeds are better than bare soil. Some types of weeds will neither bloom nor disperse seed if mown. However, many types adapt to mowing by merely blooming and seeding lower. Dandelion and foxtail are notorious for their defiance to mowing.
Weeds are very efficient and creative with the dispersion of their seed. It is impossible to prevent seeds from coming into the garden from the outside. Yet, it is still best to inhibit the production and dispersion of seed from within the garden. Spurge and oxalis bloom and disperse seed in secret before they seem to be mature enough to bloom. Other weeds have taller or more prominent blooms that can be cut down before producing seed, even if the weeds are not actually removed completely.