How to Kill Weeds

Pulling weeds is often a dreaded chore, but if you are tempted to let weeds grow another week or two, consider this: Redroot pigweed (Amaranthus retroflexus) is an annual weed that invades most flower beds. It produces 1 million seeds each season, which remain viable in soil for up to 40 years. Pulling just one weed eliminates almost one million new weeds for four decades. Let the case of pigweed be your motivation.

Weeds rob garden plants of light, water, nutrients and space to grow above and below ground. Weeds can host unwanted insects and spread diseases. In some cases, weeds affect human health causing skin rashes and allergies.

Pulling plants by hand is the most targeted way to eliminate plants you consider weeds. It is important to hand-pull weeds before they flower and turn to seed. Pull them as soon as they emerge.

If the weed is mature with strong roots, the hand pulling is easier with wet soil. Saturate the top 6 to 8 inches of soil around the weeds. Using your entire hand, reach down below the soil line and grasp the top of the taproot. With a firm grip on the taproot, pull straight up in a twisting motion. Twisting the weed breaks the taproot free from the feeder roots. If the weed is an annual, removing the taproot ensures that same weed will not be back this season. If the weed is perennial, any small pieces of root remaining can grow into a new plant. Perennials often require chemical herbicides.

There is no single herbicide that kills every type of weed. To find the proper chemical treatment for your weed problems, you must know the type of weeds you have. There are four types of weeds: broadleaf, grass, sedge and aquatic. Broadleaf weeds have wide leaves with veins branching out across each leaf. Grass weeds have flat stems and narrow leaves arranged in sets of two. Sedge weeds have narrow leaves in sets of three and aquatic weeds live in water for part of their growth cycle.

The categories for herbicides are pre-emergence selective, post-emergence selective and post-emergence non-selective. Pre-emergent selective herbicides are mixed into the top 1 to 2 inches of soil. They kill grass and broadleaf seedlings as they germinate. They do not kill emerged weeds. Examples of this herbicide category include DCPA, trifluralin, bensulide, dichlobenil, EPTC, simazine and oryzalin.

Post-emergence selective herbicide is used when broadleaf weeds are emerged and growing. The product can drift and damage other plants. Examples of this herbicide are 2,4-D, MCPP and dicamba.

Non-selective post-emergence herbicide is applied to broadleaf and grass foliage after weeds are emerged and growing. It cycles through the weed, killing the roots of annuals and perennials. Drifting spray is a significant danger to other plants in the garden. It breaks down in soil. Glyphosate and triclpyr are examples of this category.

When choosing a chemical herbicide, read the label carefully to determine if the product targets the types of weeds you have. You may need more than one herbicide. Do not mix products.

Chemical herbicides are approved by a number of government agencies before being sold to the public. When used as directed, most herbicides are safe for people and animals. Here are some additional precautionary measures to follow:

• Always leave herbicides in their original containers and keep out of reach of children. Do not pour any unused herbicides down the drain, on the ground, in streams or in ditches.

• Wear protective clothing including a long-sleeved shirt, long pants, socks, shoes, safety glasses and gardening gloves. Wash skin after applying chemicals.

• Only use one sprayer for each kind of chemical and label the sprayer accordingly.

• Do not eat, drink or smoke while applying chemical herbicides. Avoid touching your eyes, mouth or skin while working.