What is shepherd's purse?

Shepherd’s purse is a common annual weed of both cultivated and bare ground. Plants produce vast quantities of seed throughout the year, which germinate quickly, meaning it can easily become a nuisance in beds and borders.

Appearance

Rosettes of variably shaped and toothed green leaves grow from a long, skinny taproot. Small, white flowers are borne on slender racemes 30-40cm (1ft-16in) tall and quickly followed by distinctive heart-shaped seedpods. Foliage and flowers may be produced year-round, but commonly it is only the rosette which overwinters, with flowers produced in spring.

The problem

A single plant is able to produce an average of 2-3000 seeds each, with three generations per year. Seeds are long-lived in the soil and will germinate quickly if brought to the surface by cultivation.

The weed is also a common host plant for the foliar disease white blister, which affects members of the Brassicaceae, Asteraceae and Aizoaceae. Shepherd’s purse may harbour the disease, increasing the chance of it spreading to ornamental and edible plants in these families. The weeds can also act as a reservoir to maintain the disease in a garden, even when susceptible plants are not being grown.

Control

Non-weedkiller control

Eradicating the weed using non-chemical approaches can be difficult and requires time and patience. However where the weed occurs in beds and borders, these approaches may present the most effective and practical control:

• Regular light hoeing of seedlings soon after they appear will sever rosettes from their taproots and prevent flowering and seed production. Use a long-handled hoe to quickly tackle a border and a hand hoe for weeds growing near or between established plants. Non-flowering seedlings can be composted
• Applying organic mulches, such as bark chips, to affected beds and borders will prevent growth if applied to a depth of at least 8cm (3in). Opaque mulching films are also effective

Weedkiller control

In beds and border

The contact herbicide pelargonic acid (Doff 24/7 Fast Acting Weedkiller, Roundup NL Weed Control, Resolva Xpress Weedkiller) fatty acids (SBM Solabiol Super Fast Weedkiller) or the systemic herbicide glyphosate (Roundup Fast Acting) can be used in such situations to scorch off foliage. This should be done before plants produce seed. Take care if applying these non-selective herbicides between ornamental plants by covering them with plastic sheeting whilst spraying. Covers can be removed once the spray has dried on the weed foliage.

In uncultivated areas or around established trees and shrubs

SBM Job done Tough Weedkiller (ready-to-use only), SBM Job done Path Weedkiller (ready-to-use only) and Weedol Pathclear products containing glyphosate/diflufenican and can be applied once a season to natural surfaces where no plants are to be grown, and can also be applied under and around established woody trees and shrubs. This product kills off existing small green growth and prevents or checks developing growth. Check manufacturer’s recommendations before use to avoid damaging sensitive plants.

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 sections 3, 4 and 5). 

Links

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