Friday, March 5, 2021

Chemical Control of Weeds in the Flower Garden


The traditional methods of weed control in flower plantings consist of manual cultivation, hand pulling and mulches. However, in recent years chemical companies have introduced a number of herbicides for the home gardener. These weed killers have been formulated and packaged by lawn and garden supply firms and sold through garden centers, hardware stores and other businesses dealing in garden products.


Generally, herbicides are categorized for use as post-emergence or pre-emergence. The former refers to products sprayed directly on the weed. These types, such as liquid 2, 4-D and Amitrol-T, cannot be used safely in flower gardens due to the likelihood of injury to desired plants. Pre-emergence herbicides are applied to the soil before germination of weed seeds. This type of herbicide kills germinating seeds or young seedlings but will not affect existing weeds. Pre-emergence herbicides will be the subject of the remainder of this fact sheet.

Proper Selection Important

At this time no herbicide will control all weeds, nor is one safe to use around all flowers. The user must read the label and follow directions with respect to type of weeds that will be controlled and ornamentals tolerant of the herbicide. Too often, applicators believe that once an herbicide has been applied, all weeds will be controlled. This is usually not true, particularly with perennial weeds such as dandelion, bindweed, quackgrass and thistle. Select the herbicide for your yard depending on weeds normally present and flowers to be grown.

Cultural Factors

Several cultural factors are important for successful results with pre-emergence herbicides. Knowledge of one’s soil type is helpful. Certain products, such as those containing trifluralin and oryzalin, are more effective in lighter, sandy soils, while chloramben is most active in clay loam soils. The soil should be moist before application or the application followed by rain or irrigation. Herbicides applied to dry soils without rain or irrigation for 7 to 10 days will often fail as weeds will germinate before the herbicide becomes active. The soil should be weed free at the time of application and preferably freshly tilled, cultivated or hoed. Effectiveness of herbicides is improved if the product can penetrate the soil with water 1/2 to 1 inch deep. Mulching following application of an herbicide enhances effectiveness. Should some weeds germinate prior to the expected weed control period of four to eight weeks, shallow cultivation can be done. Cultivation or hoeing up to 2 inches deep often extends the weed control period; however, avoid disturbing the soil more than 2 inches or the weed killer becomes too diluted within the soil.


Most herbicides are suggested for use on an area basis. Thus, it’s important to know about how much area is included in the beds to be treated. Once the area has been calculated, weigh or determine the amount of herbicide needed for a bed and apply with the equipment suggested on the label. In certain instances, it’s advisable to rent sprayers or granular applicators from tool rental agencies rather than applying with equipment that cannot be calibrated properly. Always make certain all application equipment is calibrated properly prior to use. Following use, thoroughly clean the herbicides from the equipment.

Recommended Herbicides

The underlined products represent one trade name; there may be many for each product. In parentheses is the common name, which must appear on the label. If the trade name listed is not available, ask for it by its common name. For example, DCPA at one time was the ingredient in 24 products, Dacthal being just one.

  • Betasan or Lescosan (Bensulide): The granular form is recommended to control annual grasses. Incorporate and irrigate after application Registered for use with 24 herbaceous plants.

  • Dacthal (DCPA): Wettable powder and granular forms available to control annual grasses and some broadleaf weeds. Recommended for use with 62 types of flowers.

  • Devrinol (Napropamide): Excellent for cool season weed control in spring and autumn. Use with aster, chrysanthemum, dahlia, daisy, geranium, gladiolus, petunia, zinnia and daffodils.

  • Eptam (EPTC): Incorporate 6 inches deep before planting to control annual weeds and possibly some perennial weeds. Safe to use with alyssum, ageratum, amaranths, aster, balsam, begonia, chrysanthemum, dahlia, daylily, dianthus, nasturtium, marigold, pansy, petunia and zinnia.

  • Furloe Chloro IPC (Chloropropham): This compound is especially effective in controlling annual grasses, chickweed and dodder. It is recommended for 23 herbaceous plants, including bulb, corm and tuberous crops such as daffodil, dahlia, dutch iris, gladiolus, lily and tulip.

  • Surflan (Oryzalin): Controls annual grasses, chickweed, purslane, lambsquarter and pigweed. One-half inch of water is necessary to activate the herbicide following application. It is labeled for begonia, mums, gazania, geranium, impatiens, marigold, pansy, petunia and zinnia.

  • Treflan (Trifluralin): Best against annual grasses in sandy soils. Apply before planting and incorporate 2 to 3 inches in soil. Labeled for more than 40 flowers.


  • Thoroughly read the label and follow directions. Do not use on vegetables, turf or other crops not on the label.
  • As a result of varying environmental conditions, herbicides do not always result in the same degree of control each year.
  • Pay particular attention to timing and apply as directed before planting or following the suggested period of establishment.
  • A trial plot in a small section of the flower garden is suggested the first time herbicides are used.
  • If herbicides are spilled on skin, wash thoroughly with soap. If swallowed, in contact with the eyes or absorbed to the point or showing symptoms, call a doctor immediately.

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