The RHS believes that avoiding pests, diseases and weeds by good practice in cultivation methods, cultivar selection, garden hygiene and encouraging or introducing natural enemies, should be the first line of control. If chemical controls are used, they should be used only in a minimal and highly targeted manner.
On a small scale plants can be dug out by hand. In larger areas improving drainage by installing land drains will discourage the sedge, as will liming to reduce acidity. Cut plants regularly to prevent seeding of Carex pendula and C. binervis (C. hirta grows from a rhizome and seeds much less).
In lawns and meadows: Apply a high nitrogen fertilizer to encourage strong growth of the other grasses. Selective mowing of the sedge will help limit its spread. If in a meadow situation, goats give good control of rushes (Juncus) and sedges (Carex).
In lawns and meadows
Carex are resistant to selective lawn herbicides. Individual plants can be spot-treated with a ready-to-use spray containing glyphosate. Glyphosate is a non-selective, systemic weedkiller applied to the foliage. When the sedges are killed, raking in some grass seed will help the bare patch to regrow quickly. Where weed infestations are heavy, the whole site may need to be sprayed off and reseeded. Chemical control is unlikely to be effective unless done in conjunction with improving drainage.
In uncultivated areas
If the site is heavily infested with sedge seeds, only thorough fallowing may clear the site. This is achieved by clearing the site of vegetation, preparing a seed bed, then allowing the sedge seeds to germinate, killing them (with a contact weedkiller such as Weedol Gun! Fast Acting), then cultivating again to bring more dormant seeds near the surface. The new seeds on the surface will then germinate where they can be sprayed off. The operation should be repeated, if necessary 3 or 4 times, until the top 2 or 3 inches of soil have been virtually cleared of dormant sedge seeds.
Inclusion of a weedkiller product does not indicate a recommendation or endorsement by the RHS. It is a list of products currently available to the home gardener.
Weedkillers for gardeners (Adobe Acrobat pdf document outlining weedkillers available to gardeners; see section 3 and 4)
Chemicals: using a sprayer
Chemicals: using safely and effectively
Chemicals: using spot and broad-scale
Weeds: non-chemical control