Not to be confused with patching, overseeding is the planting of new seed into an established turf area to extend its time of use. Usually the grass being applied is different from the established species. The practice of overseeding has been common on southern golf courses for many years. As the autumn and winter seasons begin, the warm season grasses go dormant and turn brown. The application of a rapidly germinating cool season grass that thrives in the reduced temperatures brings back the green that golfers want to see. Another common use of overseeding is on athletic fields where the established turf, such as Kentucky bluegrass, wears away before the season ends, so overseeding with a rapidly germinating perennial ryegrass can bring back the lush green appearance in only a few weeks. It is usually done in conjunction with aeration, since it is important to get the seeds in contact with the soil.
Overseeding is enjoying increasing popularity as a maintenance technique for commercial landscapes. Its appeal to homeowners is less dramatic, but increasing nonetheless.
Weed Control in Established Lawns
Turfgrass plantings can be marred by the presence of weeds. The weeds may include undesirable grasses and broadleaf plants. They may be annuals, biennials, or perennials. Many are prolific seed producers and infiltrate the lawn each year, often invading from the lawn of a neighbor who is not conscientious about control. Other weeds are indicators that something is wrong with the lawn. For example, certain weeds are predictable where the soil is too compacted for healthy grass growth. Others are found where winter pavement salt has killed off the turf.
For a review of weeds and herbicides, see Chapter 6. Preemergence herbicides are used to control many weeds in lawns and must be applied several weeks in advance of the weeds’ germination to be effective. The time of application will vary depending on the region of the country and the weeds involved. Preemergence herbicides are the preferred means of controlling annual grass weeds.
Postemergence herbicides are used against weeds that have already germinated and are visible in the lawn. They are usually applied to the lawn rather than to the soil. They may be formulated as either contact or systemic herbicides, depending on the product. Postemergence herbicides are most often used against perennial grasses and broadleaf weeds.
Selectivity is an important characteristic of turf herbicides so that the desirable grasses are not damaged by the control effort. Annual grasses and broadleaf weeds are commonly controlled with selective herbicides. However, perennial grass weeds require the use of a nonselective herbicide (one that kills all vegetation that it touches). Nonselective herbicides must be applied on days without wind and with applicators that control the amount and direction of flow very carefully. After the treated area is free of weeds and time has rendered the herbicide harmless, new patch planting can take place.
For products recommended against specific turf weeds, turf managers can consult their local college of agriculture or Cooperative Extension Service. Because turf weed problems and recommended controls do not vary greatly from state to state, helpful information can also be found in trade journals that serve the turf industry.