Glyphosate is deactivated on contact with soil. It only works by absorption through the green part of plants. Grass seed could be applied straight after the application of the weedkiller but realistically it is better to wait until the weeds are dead as it may be necessary to retreat some of the more persistent weeds […]
Persistent weeds must be removed before they take over completely or build up a large bank of seeds in the soil for future years. Regular hand weeding or can help, but relatively large areas need to be sprayed using a concentrated lawn weedkiller, such as Verdone.