Bittercress

Bittercress may be small and short-lived but its ability to produce and disperse large amounts of seed makes it an exacerbating weed. Often introduced unwittingly on the compost of container plants, it can be hard to be rid of in a garden.

Bittercress

Quick facts

Common name bittercress, hairy bittercress, wavy bittercress
Latin name Cardamine hirsuta (hairy bittercress), C. flexuosa (wavy bittercress)
Areas affected surface of containers, bare soil, paths
Main causes weed with explosive seed capsules
Timing remove whenever seen

What is bittercress?

Hairy bittercress (Cardamine hirsuta) (see image above) is an annual species, common throughout the British Isles, particularly on bare ground, path-sides, and on walls. It may often be seen growing on the surface of containers in nurseries and garden centres and the seeds can be introduced into gardens unwittingly with container-grown plants.

Wavy bittercress (Cardamine flexuosa) (see image below) is a biennial or perennial plant, common in moist shady places, such as by streams, throughout the British Isles. It may occasionally be troublesome in gardens, usually in moist or poorly drained soils.

Appearance

Related to the pretty cuckoo flower (Cardamine pratense), bittercress is a much drabber plant with insignificant white flowers and pinnate leaves. The arrangement of flowers and seed heads is typical of members of the mustard family (Brassicaceae).

Hairy bittercress (C. hirsuta) is the smaller of the two, sometimes growing just a few centimetres. Wavy bittercress (C. flexuosa) can grow strongly to reach around 50cm (18in) in height in damp conditions but is usually shorter in gardens.

The problem

Bittercress has an explosive seed mechanism by which seeds can be dispersed up to 1m (3ft) away or considerably further if carried by the wind. As with all annual weeds it is essential to destroy it before seed can be produced.

Cardamine hirsuta has a short life cycle. Seedlings may appear at most times of the year, but mainly in the summer or early autumn. As it is frost hardy it can survive the winter and will flower as temperatures rise in early spring, producing several generations in a season. Cardamine flexuosa is longer-lived but is less common as a weed in gardens.

Control

Non-weedkiller control

Cultural control methods are more successful if applied before the weed has had time to set seed. Where infestations of bittercress are light, fork out before the weed sets seed. Among ornamentals or vegetable crops, careful hoeing or hand weeding is the only practical means of destroying either weed. If, however, they have been allowed to seed, they may remain a recurring problem for some time.

On borders or bare soil, a deep mulch (15cm (6in)) of organic matter such as garden compost or bark should help suppress the weed.

Weedkiller control

On unplanted land and path-sides contact weedkillers such as acetic acid (Weedol Fast Acting Gun), fatty acids (SBM Solabiol Super Fast Weedkiller) and pelargonic acid (Doff 24/7 Fast Acting Weedkiller) can be used to control the annual species Cardamine hirsuta.

With heavier infestations of Cardamine flexuosa apply the herbicide glyphosate (e.g. Roundup Fast Action, SBM Job done General Purpose Weedkiller or Doff Glyphosate Weedkiller), letting the weed grow to flowering stage before application. When using glyphosate take care to avoid leaves and other green parts of all garden plants as it is not selective in action. Used with care, glyphosate is safe to use around the base of non-suckering woody plants, as long as the bark is woody, brown and mature. Glyphosate is not active through the soil and there is therefore no risk garden plants will absorb it through their roots.

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 3 and 4)

Links

Chemicals: using a sprayer
Chemicals: using safely and effectively
Chemicals: using spot and broad-scale weedkillers
Weeds: non-chemical control


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