UNITED STATES—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 prompts 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.
Some of the biggest and nastiest weeds are thistles. The most common is annual sowthistle, which can get taller than four feet in just a few months. It is relatively easy to handle, since the bristly foliage and stems are somewhat soft, almost like coarse lettuce. Blessed milkthistle is much nastier, with sharp foliar spines that can penetrate boots! It can get more than five feet tall and broad!
Most thistles are biennials or perennials, with spiny lobed foliage. They produce low foliar rosettes during their first year, and then bolt and bloom on tall floral stalks during their second year. Biennials usually die after bloom, but sometimes regenerate from the roots later. Perennials are more likely to regenerate and bloom annually for several years. Some thistles get rather shrubby.
The roots of many types of thistle would not be too difficult to pull from well watered soil if only the spiny foliage were not so difficult to handle. Larger plants might be easier to pry out with a shovel. If foliage is merely cut off at the the surface of the soil, it will regenerate from the large tap roots left below. However, cutting down flower stalks before bloom interferes with seed dispersion.