Common Purslane (Portulaca oleracea) is an annual weed that reproduces by seed. Its leaves and stems are fleshy and succulent, often tinged slightly red. The stems grow prostrate over the soil surface, and root easily if the main root system has been disturbed.
Purslane is usually more of a problem in flower and vegetable gardens, or other areas where the ground has been disturbed, than it is in lawns. In gardens, pre-emergent herbicides such as trifluralin (Treflan, found in Greenview Preen) and dacthal (found in Ortho Garden Weed Preventer) can be used in spring to keep purslane seeds from sprouting. These herbicides also prevent many flower and vegetable seeds from sprouting so be sure to read and follow label instructions carefully. You will probably have to wait until flower or vegetable seedlings are up and growing before applying pre-emergent herbicide to the bare soil surrounding them.
Covering bare soil with mulch is another way to keep purslane from sprouting. In an unmulched garden, you can slice off purslane with a sharp hoe. Deep hoeing is unnecessary. Slice the weeds off frequently; their roots will run out of stored energy and give up. Don't leave cut purslane lying around if the ground is moist, though. Plants can re-root if conditions are favorable.
Purslane is rarely a problem in a well-maintained lawn. Regular watering, fertilizing, and mowing usually keeps turf thick enough that purslane can't compete. The best way to control purslane in the lawn is to concentrate on improving the lawn itself.
If purslane is a problem in your lawn, you can prevent most of it by applying a pre-emergent herbicide meant to control crabgrass in early May. Good pre-emergent purslane control chemicals include Dacthal, Balan, Betasan, or Tupersan (siduron), and others as their active ingredients. These chemicals are usually mixed with lawn fertilizer, but are sometimes packaged separately.
If you are planning on seeding a lawn in spring and still wish to control annual weeds, use the herbicide containing Tupersan (siduron). This chemical will not prevent the germination of desirable grass seeds. All others will stop grass seeds right along with the weed seeds.
You can also use a broad-leaf herbicide containing 2,4-D and MCPP to eliminate purslane, as long as there is no young grass in the lawn. It is most effective when purslane is still small, temperatures are between 60 and 85 degrees, wind is calm, and no rain is expected for at least 24 hours. As always when using a pesticide, read and follow label instructions carefully, and try to target only weedy areas in the lawn to reduce unnecessary pesticide use.