Application of chemical herbicides can be a useful strategy for controlling weeds in flower gardens. Attention to soil conditions can help maximize herbicide effectiveness, while care in timing and application will ensure that your flower garden is safe from any unintended herbicide damage. Different kinds of herbicides work best in different environments and at different points in the plant growth cycle, so plan ahead to find the chemical herbicide appropriate for your flower garden requirements.
Herbicides are classified into general types: preemergent and postemergent. Preemergent herbicides are placed in or on the soil to deter weed seed germination. Postemergent herbicides are sprayed directly on the growing weed. Postemergent herbicides require caution to avoid the danger of killing desired flower plant specimens along with the weeds, while preemergent herbicides take forethought and planning, and may not be as effective.
Postemergent herbicides like glyphosate (such as the brand Roundup, from Monsanto) present challenges when used in an established flower garden. The best time to use chemical herbicides is before the flower garden is established, to eliminate perennial weeds like quackgrass and mugwort before you install your ornamental plantings.The Cornell University Cooperative Extension Service recommends applying glyphosate at high applications in the fall to areas intended for flower garden planting the following year.
Weeds compete with flowers for nutrition, water and, if left to get overgrown, even sunlight. Hand weeding, boiling water or propane-torch weed killers, along with heavy mulch to deter weed emergence, are the most environmentally sound methods of weed removal, and are also safest for your flower plants and your health. However, these methods may well be too time-consuming for use in large estate or business landscape flower gardens, or when reclaiming a neglected home flower bed which has been overrun by weeds. Hands-on weed removal may also be difficult when the weeds in question are poison ivy or prickly things like nettles or burdock. Chemical weedkillers provide time-efficient weed control over large areas without scratching up your arms.
The Ohio State University Extension Service recommends that you understand your soil type and consider soil moisture levels before choosing the most effective appropriate herbicide for your flower gardens. Trifluralin- and Oryzalin-based herbicides (like brand-names Treflan and Surflan) work best in sandy environments, while chloramben herbicides are recommended for clay. Water is necessary to activate most herbicides; application during a dry spell will render them ineffective. Water before applying the herbicides to the soil, then mulch to retain the moisture content while the chemicals go to work.
Faculty at the Penn State College of Agricultural Sciences warn that spraying herbicides can create drift or fumes that damage or even kill other plants at considerable distances from the intended target. Avoid spray drift by applying herbicides only on very still days, and never use a sprayer for fertilizer or other applications once it has been used for herbicides.
Different herbicides have been related to a variety of negative environmental and human health effects. The U.S. Department of Health and Human Services maintains a Household Products Database which lists the required warning label advice for each common garden herbicide (See Resource 2). The warnings regarding Roundup, for example, indicate that it is toxic to fish and aquatic invertebrates, so care should be taken to ensure it does not reach water sources. This herbicide may also cause temporary skin and eye irritations or allergic reactions in humans. Faculty at the University of Florida Agronomy Department note that most modern herbicides have a toxicity rating considerably less than that of table salt--but ordinary precautions should still be taken in any herbicide application.