There is now a product on the market which is certified organic - it is not systemic and does not harm earthworms or soil life. It works by dehydrating the foliage by intercepting the transpiration process, causing cell collapse and root stress. The product is a restricted input under Bio-Gro certification.

Otherwise, Richard Llewellyn Hudson, author of Organic Gardening in New Zealand, says that hoeing off the new growth in the weeks following cultivation will knock out a lot of weeds. This is followed by laying on as much compost as possible to smother new seedlings. Don't allow annuals to shed seed or put seeding weeds in the compost, unless your compost is hot enough to kill them. Laying thick layers of newspaper topped with a thick layer of mulch will starve them of light, a process done during the growing months, rather than when seeds are dormant. Once they are cleared, keep them at bay with mulch.

He says that digging is often the only way of ridding the ground of the perennial deep-rooted weeds which compete with food plants, but avoid bringing the subsoil to the surface.