Dear Ivamae,

Thank you very much for your inquiry. Purslane can be a difficult weed to control. Your black plastic idea could work, but it will only solve the problem temporarily as there is a large seedbank in the soil for the weeds to come back from time after time. (For chemical control, you can use either Bayer Advanced All-in-one or Ortho Weed B Gon MAX plus crabgrass killer, as they both have quinclorac, an excellent herbicide for this weed) The first thing we need to realize is that weeds are opportunists and are growing where we allow them to grow. Weeds are not the cause of poor turf, but rather the effect of poor turf management. So, once we control the weeds we must do something to promote the turf, if possible.

The big question is how the other cultural practices are contributing to your weed population, namely mowing, fertility and watering. If these are out of balance, putting down the weed killer can get pretty tiresome as the results will not be dramatic. Since I do not know the particulars about your actual lawn, let me start with some general guidelines.

To begin with, you must mow frequently and follow the one-third rule. This means never cut more than one-third of the leaf blade off in any single mowing. This promotes turf density and the density is the key to preventing the light requirement for the weed to germinate. Second, follow a balanced nitrogen fertility plan. Apply judicious amounts of nitrogen when the grass is actively growing. For cool season grasses, this centers on spring and fall and for warm season grasses, late spring and summer. Do not over fertilize as this will cause rapid growth and then you will end up scalping the grass if you cannot keep up with the mowing and then weeds can encroach.
The final issue is watering. This one is not straight forward as climate, soil type, grass, and time of year will dictate the water needs of the plant. One rule to begin with is to assume that your turf will need 1.0 inch of water per week during the growing season. This can be applied in a variety of ways and rainfall needs to be counted in the total. For best results, try to water early in the morning. The wind is at it least and you can be the most efficient with the least contribution to disease pressure.

Again, thanks for the question and let me know if you have more.

Respectfully

Trey Rogers, The Briggs & Stratton Yard Doctor, YardDoctor.com

I didn't make myself real clear.

This was a vegetable garden area with no grass. I got compost from the city and then got the matt of purslane. I want to get the weed killed so that I can put grass seed on it. I hate the thoughts of seeding it with all this weed. There is presently a channel iron frame work around this large area and it has not gone outside of this - at least not to any extent. I want to eventually be able to remove this channel iron , seed this, so that it is included in the lawn.