In the vegetable garden, there are annual and perennial weeds. Control and prevention steps vary somewhat with the type, so it is helpful to know which of your weeds is an annual (returning each year by seed) or a perennial (returning each year from over-wintering roots).
Most common weeds in vegetable gardens are annuals. Although they sometimes seem to survive all efforts to kill them during the growing season, they do eventually die at the end of the season. However, if they are permitted to spread their thousands of seeds before they die, their progeny will crop up next season. Annual weeds are highly prolific and produce enormous numbers of seeds per plant. For example, a single chickweed will produce 15,000 seeds, shepherd's purse will put out 40,000 seeds per plant, and lamb's-quarters is right up there with 70,000 seeds. These seeds lie in the soil, just waiting for the light, warmth and water they need to germinate for the new season.
While annual weeds are relatively easy to kill (step one), prevention (step two) takes some effort. The key to preventing the return of annual weeds is to control their seeding activity . To prevent them from emerging again next year they must be killed before they have a chance to release seed.
It is the perennial weeds that represent the most serious problem in a vegetable garden. Plants like creeping charlie, plantain, thistle, poison ivy, and clover require very direct attention. They are tough plants that often grow right through a heavy mulch. Again, to get rid of perennial weeds for the season (step one) does not truly solve the problem. It is necessary to prevent perennials from returning (step two) which means their roots must be killed. They tend to have amazing root systems, which make them extremely difficult to prevent and eliminate. Leafy spurge, for example, has roots that grow 4 to 8 feet deep, while Canada thistle's roots may penetrate to depths of 20 feet! It's no wonder that these weeds are very difficult to completely root out. In most cases, any small piece of the root inadvertently left in the ground will regenerate the plant.
Identifying Annual Vs. Perennial Weeds
If you pull a weed and it grows back in a few weeks, you can generally assume that it is a perennial weed. While some are vinelike, spreading over the ground by means of underground runners, most are individual plants. They thrive in inhospitable soil and seem able to live without water indefinately. They are stubborn, tough plants capable of growing right through a heavy mulch. Many of us have been astounded to discover these weeds growing through an asphalt driveway.