Weeds can make ornamental plantings look unsightly. Weeds also may harbor insects and diseases that may cause problems on more desirable ornamental plants. The weeds will also compete for light or use water and nutrients that ornamental plants could use for growth. Successful weed control depends on preventive methods, proper weed identification, and the timely use of cultivation or chemicals.
Perennial weeds come up every year from the same roots. These are the most difficult weeds to remove. Many hard-to- control perennial weeds are brought into the landscape as perennial flowers or as ground covers. The plants then escape and become weeds (plants out of place). Chemicals that kill these plants will also kill ornamental plants.
Annual weeds come up from seed each year. These can be somewhat easier to control because the pre-emergence herbicides will kill the seedlings before they emerge from the ground. Mulching and cultivating are other options that control annual weeds. Annuals vary in the time of year when the seed germinates, so some can become problems at the end of the growing season.
Herbicides can be used effectively to control weeds. Unfortunately, these useful chemical tools are often misused. Weed control chemicals are designed to kill plants. Many chemical controls do not differentiate between weeds and ornamental plants. If they are applied improperly, they can injure ornamentals. The most serious problems occur when total vegetation killers are used to kill grass around trees and shrubs. Once they reach the roots, these chemicals will also injure the trees and shrubs.
Timing of herbicide applications is important. Pre- emergence herbicides will not control weed seedlings if they are applied after the seedlings have begun to grow vigorously. Young weeds are easier to kill than old, established weeds. Post-emergence herbicides are used on existing weeds.