Lawn sand is a combined weedkiller and lawn fertiliser, (comprising ammonium
sulphate, iron sulphate and fine sand). It should be applied between April and
September, in dry conditions, but preferably when rain is expected within a
couple of days. Follow the application instructions on the packet, but do not
exceed the stated application rate otherwise the grass may be killed. It will
probably turn black but quickly recover. Annual use, will also keep worms, and
therefore worm casts off the lawn.