What is a weed?

Any plant that is unwanted, out of place, or just has no discernable value can be considered a weed. Approximately 3% (8,000 of 250,000) of plant species found worldwide are classified as weeds.

Types of weeds

Weeds are typically grouped into 2 categories based on their plant structure:

• Broadleaf weeds usually have flat leaves, net-like veins, and grow by means of a taproot or coarse root system. When they first germinate, two leaves emerge from the seed.
• Grassy weeds grow narrow, upright leaves and have parallel veins. They sprout only one leaf from the seed pod and develop a finer, more fibrous root structures.

Weed life cycles

Weeds are also classified by their life cycle. Just like flowers and other desirable plants, they can be annual, biennial or perennial.

• Annual weeds sprout, flower, seed, and die, completing their life cycle, within one year or less, and can be further divided into summer annual and winter annual species—depending on when they begin to grow.
  • Winter annual weeds germinate from seed in the cool soil of fall and early winter, then grow and flower early the following year. After dropping their mature seeds, they die. Examples are common chickweed, hairy bittercress, henbit, purple deadnettle, speedwell, and annual bluegrass.
  • Summer annuals germinate in the spring or early summer after sitting dormant all winter. These weeds grow all summer before dying in fall, usually when frost arrives. Examples include crabgrass, foxtail, purslane, pigweed, lambsquarters, spotted spurge, black medic, groundsel, and yellow woodsorrel.
• Biennial weeds take two years to germinate, bloom and die. They are the least common type of weed and will germinate in any growing season. Examples include bull thistle, wild carrot, prickly lettuce, and common mallow.
• Perennial weeds live at least two years and have the potential to reproduce indefinitely. If you don't remove the entire root system, they'll grow back again and again. Examples include dandelion, white clover, plantains, wild strawberry, Canada thistle, and california buttercup.

To find a weed and the Preen product to get rid of it, please visit our Weed ID.

Why control weeds?

Weeds rob plants of nutrients. Weeds deprive desirable plants of needed water, light, and soil nutrients.

Weeds can be harmful to us. Some weeds can scratch and irritate skin, aggravate allergies, and even harbor insects and diseases.

Weeds are opportunists. Weeds are simply nature’s way of quickly covering up bare ground. They are opportunistic and aggressive and genetically designed to germinate, grow, and propagate faster than most desirable plants.

Weeds spread easily. Weed seeds are specially adapted to spread. Their seeds are widely distributed by animals, insects, hay, mulch, topsoil, and by air. Once they find their way to your lawn and garden, they can remain there. While most weed seeds only exist in the soil for a few years, some can remain dormant for decades, waiting for the right growing conditions to sprout.

Weeds can be prolific seed producers. Most plants only produce several hundred seeds, but weeds are especially prolific. One single weed can produce anywhere from 10,000 to over 100,000 seeds. With these odds, it’s easy to see how weeds can quickly take over your garden or lawn if left untreated.