Fall Weed Control - photo by Soni Cochran

Weed Control in Landscape & Gardens

submitted by Sarah Browning, Extension Educator

Nothing takes the fun out of gardening like pulling weeds. So instead of ignoring weeds until they get out of hand this year, why not develop a plan for controlling them that takes as little time as possible and lets you spend your energy on more enjoyable activities?

The two main weed control techniques are 1) cultural methods, such as cultivating, hoeing, and mulching, or 2) the use of herbicides. Generally, cultural weed control provides good results, but in certain instances herbicides have distinct advantages. For example, if a garden plot is overgrown or is being established in a new location, chemicals help control large numbers of pre-existing weeds that might otherwise be difficult to eradicate.

These weed control techniques don't have to be exclusive; in fact, they work best when used together.

Cultural Weed Control

Organic mulch is your best friend when it comes to weed control. Not only do mulches control weeds, they also prevent the evaporation of moisture in the soil and keep the soil cool. This can help maintain uniform soil moisture, which results in better quality fruits and prevents some plant health problems, such as blossom end rot in tomatoes. As it breaks down, mulch adds organic matter to the soil, improving soil structure, and creating a better growing environment for garden plants, too. Maintain a 2-3 inch layer of organic mulch, such as newspaper, chopped leaves, pine needles, wood chips, shredded hardwood, or herbicide-free grass clippings, in all planting beds, throughout the summer.

Sheets of plastic can be used in the vegetable garden as a method of weed control, and work well when used in conjunction with drip irrigation. Weeds are smothered and overheated under the plastic layer. Vegetables are planted through individual openings, and water is delivered only to the vegetable plants, and not to weeds. The plastic is taken up at the end of the growing season. Hoeing, pulling weeds by hand and using mulches to smother weeds or prevent them from germinating are common cultural methods of weed control. Timely hoeing and weeding, done when weeds are still small, can limit weed problems before they become overwhelming. A quick weekly walk-through of landscape beds to hoe out any newly germinated weeds can provide good control throughout the summer. Weed Control with Herbicides If applied correctly, herbicides decrease labor, time and plant competition, often an appealing prospect when crab grass begins to overtake gardens in the heat of summer. Herbicides can be particularly labor-saving for those with large gardens. They help control deep-rooted perennial weeds such as bindweed effectively, something that is very difficult to do organically.

Two types of herbicides can be used, pre-emergent and post emergent. Pre-emergent herbicides kill weed seeds as they germinate, and work best in established gardens or landscape beds. However, if vegetable gardens are planted using seeds, pre-emergent herbicides can be applied AFTER the vegetables are up and growing. This will minimize weed pressure throughout the rest of the summer.

Pre-emergent herbicides are meant to form a continuous chemical barrier in the soil. If the barrier is disrupted by hoeing or digging, then weed seed may successfully break through. Apply pre-emergent herbicides after a 2-3 inch application of mulch for best weed control.

Post emergent herbicides are applied to kill weeds that are already growing. Spot applications are best; they result in the smallest amount of herbicide being used, saving you money and protecting the environment. Many post emergent herbicide products are available, and you need to know two things about the weed to be killed for good control; 1) is it an annual or perennial, and 2) is a grassy or broadleaf weed. You also need to consider the plant or crop where the weed is growing and if it will be damaged by the herbicide you plan to use. For specific recommendations on post emergent herbicides, talk with your garden center professional, or consult with your local extension office. To find your local office, visit here.

However, herbicides cost money and must be used with caution. Always read and follow label directions, paying particular attention to the label's listing about crops where each herbicide can be used. Remember, the label is the law. Always apply herbicides carefully to avoid drift onto susceptible crops or landscape plants.

Pre-emergent Herbicides

The most common type of landscape pre-emergent herbicide is trifluralin, most commonly sold as Preen Garden Weed Preventer. It is labeled for use in landscape beds, around trees and shrubs, non-fruit bearing fruit and nut trees, and in the vegetable garden. Trifluralin breaks down in sunlight, so should be watered into the soil immediately after application.

A second pre-emergent product available for home gardeners is corn gluten meal, sold as Wow, Concern, or Preen Organic. Corn gluten meal is a natural by-product of the corn wet milling process, but it provides both pre-emergent herbicide activity and some nitrogen when used in the garden or landscape. It can be applied around established vegetables, herbs, and fruits, as well as landscape beds.

Make the first application of a pre-emergent herbicide in your gardens when soil temperatures reach 55° Farenheit for several days in a row. Usually that happens around the first week of May. Applications of both trifluralin and corn gluten meal provide about 4-6 weeks of weed control, so the product should be reapplied as needed to provide season-long control.

The information on this Web site is valid for residents of southeastern Nebraska. It may or may not apply in your area. If you live outside southeastern Nebraska, visit your local Extension office

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