Broad Spectrum

• A broad-spectrum herbicide that contains glyphosate kills off weeds and other unwanted vegetation before flower planting. Glyphosate kills weeds by inhibiting their ability to produce proteins. In addition, liquid herbicides that contain glyphosate leave little soil residue behind that harms seeds or flowering plant's root systems. Gardeners using a broad-spectrum herbicide must be careful when using it around landscape plants or grass, because its chemicals kill off anything that the spray comes in contact with.
  
  

Pre-emergent Herbicide

• Pre-emergent herbicides prevent weed seeds from germinating. This herbicide works by creating a barrier in the soil, which keeps weeds from popping up. In order for pre-emergent herbicide to work, gardeners must apply before soil temperatures favor germination of broadleaf or grassy weeds in the early spring. For example, liquid pre-emergent herbicide that contains trifluralin must be applied before right before soil temperatures hit 50 degrees Fahrenheit. To use a herbicide that contains trifluralin, dilute the mixture in a sprayer and apply to the flower garden.
  
  

Post-emergent Herbicide

• Control grasses with selective post-emergent herbicide. Selective herbicide is chemically formulated to control grassy weeds without harming ornamental broadleaf plants. Gardeners may use a liquid herbicide that contains fluazifop to control common grassy weeds such as crabgrass, ryegrass, sedges or your own turf. When using a post-emergent herbicide, gardeners must thoroughly coat weed foliage with the chemicals without runoff. Herbicide runoff pollutes groundwater and may harm your landscape plants such as juniper trees and shrubs.
  
  

Other Factors

• Flower beds must be monitored throughout the year for weeds. Post-emergent liquid herbicides are typically employed throughout the growing season. Pre-emergent liquid herbicides are used twice a year to control both warm- and cool-season weed growth. Gardeners use pre-emergent herbicides in the spring and in the fall. It is important to check the label of the pre-emergent herbicide before using. Pre-emergent herbicides containing trifluralin prevent spinach seed germination for 12 months after use.