| One person’s weed may be another person’s wild flower, so first decide how you feel about the plant in your own yard or garden. Then, learn more about the plants you want to reduce or eliminate to determine how and when it is best controlled. Primary, is to first determine if the plant is an annual or perennial and if the plant is a grass or broadleaf. These will in large part determine how the plant can be controlled and where.
Annual weeds grow from seed each year and die at the end of the season usually by midsummer or are killed by frost (note the special case of winter annuals below). Perennial weeds on the other hand will come back year after year and often spread above ground by stems that root or below ground by rhizomes.
Broadleaf weeds are weeds that are botanically classified as dicots such as dandelions, plantain or red root pigweed. Grassy weeds are monocots with strap-like leaves and include crabgrass, quackgrass and Bermudagrass. Nutsedge looks grass-like but is actually a sedge. It is a common weed in lawn.
Following are the major groupings of weeds. The gardener should begin to recognize. More information can be found under individual listings for each group or specific weeds.
Grasses, annual:
Grow from seed each year.
Examples: crabgrass
Can usually be controlled with pre-emergent herbicides applied before the seeds germinate in the spring. Some can also be controlled with post-emergent herbicides during the growing season.
Grasses, perennial:
Come back year after year and may spread by above ground or below ground stems and/or rhizomes.
Examples: Bermudagrass, nimblewill, quackgrass
Cannot be controlled selectively in lawn using herbicides. Non-selective herbicides, such as Roundup, can be used to kill the weed grass but desirable grasses will also be killed.
Broadleaf weeds, annual:
Grow from seed each year
Summer annuals germinate in the spring and die normally by early fall or are killed by frost.
Examples: red root pigweed, lambs quarters
Pre-emergent herbicides can be applied before the seeds germinate in the spring. Many post-emergent herbicides will also give control during the growing season. Late season control may not to necessary, as frost will kill true summer annuals
Winter/spring annuals germinate in early fall, begin growth, overwinter as small plants and then make rapid growth in early spring. By early summer they have flowered, produced seed and died. Spring annuals may germinate in very early spring and likewise complete their lifecycle by early summer.
Examples: henbit, dead nettle, chickweed, cress
Pre-emergent herbicides applied before winter annuals germinate in the fall give good control.
Broadleaf weeds, perennial
Once these weeds are established they come back year after year and may increase in size. If allowed to go to seed the weeds can spread rapidly.
Examples: dandelion, plantain, wild violet, lespedeza
Many species of broadleaf weeds growing in lawns can be killed with post-emergent herbicides such as 2,4-D. Establishment of new plants can be controlled by using pre-emergent herbicides before weed seeds germinate. Some broadleaf weeds can be difficult to kill, repeat application or special herbicides may be required to give good control. See information on specific weeds. | 
