Couch grass is a common and invasive garden weed. It is a perennial grass which rapidly spreads by

Rhizomes are creeping swollen root-like structures that are actually adapted stems. Roots, stems with leaves and flowers are produced along its length. See plants such as Anemone nemorosa, bamboo, canna, border iris.

Couch grass looks like just a tuft of any grass, but underneath the ground the roots form a dense network. It spreads rapidly by means of thin, wiry and sharp-ended rhizomes.

From its tips, new shoots are produced in spring and autumn that quickly produce tufts of leaves and more rhizomes.

The network of rhizomes become entangled in clumps of herbaceous perennials and among shrubs and fruit bushes causing great problems, as they are difficult to remove. Couch can easily spread from infested lawns into adjacent borders.

Couch is usually spread from garden to garden unwittingly when small sections of rhizomes become hidden among the roots of plants or in manures or soil.

Couch is self-sterile and, as each spreading colony is usually a single clone, seeds are not often produced.

First, consider whether this can be done using non-chemical means such as digging out or suppressing with mulch. Where these methods are not feasible, chemical controls may need to be used.

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.

Cultural control

First consider non-chemical control options;

In uncultivated areas, forking out is possible in lighter soils, as much of the underground stem system is fairly shallow, but it is easy to leave behind small sections of rhizome in the ground. These quickly regrow and need to be removed before they form a new network of rhizomes.

In cultivated areas, hand weeding can be done where there are small isolated infestations among herbaceous perennials. This is best done in early spring when the plants will soon re-establish and around bulbs as the bulb foliage is dying, but is not practical around trees, shrubs and roses where roots may be considerably damaged.

Strip off infested lawns and dig out any remaining couch grass roots before re-turfing.

Weedkiller control

Glyphosate

Glyphosate-based weedkillers (e.g. Roundup Ultra, Doff Weedout Extra Tough Weedkiller or Westland Resolva Pro Xtra Tough Weedkiller) are very effective and, if correctly applied, should kill even heavy infestations of couch.

As these products are not selective, care is needed to prevent spray landing or drifting on to other cultivated plants and causing damage. Protect them with polythene while spraying and remove only once it has dried. Follow this advice for spraying:

• In spring, spray when the new growth has reached a minimum 10-15cm (4-6in) high with each shoot having not less than four or five new leaves. Spraying at this stage of growth, in mild conditions when growth is active, will usually be very effective
• If attempting control in the autumn, the best period for spraying is early October to mid-November, but before the first frosts. Try to avoid drought conditions, as results can be disappointing
• In heavily couch-infested areas it may be better to dig up cultivated plants, carefully tease out any couch grass roots that may be in the rootball and relocate them temporarily while treatment takes place. It is unnecessary to remove bulbs that have died back where no part of the plant is visible above ground
• Couch grass should die back within three weeks; but treat any regrowth as soon as possible. Do not cultivate the soil until the grass has been completely killed

Lawn weedkillers

There are no selective lawn weedkillers that will kill couch grass while leaving the rest of the grass unharmed.

Infested lawns can therefore be sprayed off with glyphosate until the grasses are fully killed. Only then can the area be dug over and prepared for re-sowing or re-turfing.

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.

Download

Weedkillers for gardeners (Adobe Acrobat pdf document outlining weedkillers available to gardeners; see section 4)

Image: © GWI/Jacqui Dracup. Available in high resolution at www.gardenworldimages.com