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.
First, consider whether control can be achieved using non-chemical means such as digging out or suppressing with mulch.
Where these methods are not feasible, chemical controls may be necessary. Choose a weedkiller that is most appropriate for that purpose by reading the label carefully before buying or using. Contact weedkillers or glyphosate-based products, which have low persistence in the soil, may suffice. Take particular care when using residual weedkillers, which persist in the soil for several weeks or months, as they can move deeper or sideways in the soil, leading to possible damage of underlying roots.
- In an established lawn, try feeding and top-dressing to improve turf vigour
- Vigorous wire raking in mid-September will remove much of the weed
- Where Oxalis corniculata persists, it may be necessary to strip the affected turf from the site and destroy it, then re-seed the area in spring or autumn
- In herbaceous borders, repeatedly hoe to kill the weed and prevent seed being formed
Oxalis debilis and O. latifolia
- Forking out is best done in the spring when the tiny developing bulbils are firmly attached to the parent plant and before Oxalis latifolia has produced seeds. Later in the season they are easily detached, causing the weed to be spread further around the garden
- On infested shrub borders apply a heavy mulch of leaf litter, and replenish as necessary to keep the oxalis well buried. The mulch may need to be maintained for several years
- In a single small bed it may be possible to remove all the soil to a depth of several inches, bringing in fresh replacement soil
Unfortunately, Oxalis corniculata (which is problematic in lawns) shows strong resistance to the full range of selective lawn weedkillers.
Some control can be gained by treating oxalis with the non-selective weedkiller glyphosate (e.g. Roundup Fast Action, SBM Job done General Purpose Weedkiller or Doff Advanced Concentrated Weedkiller). The most effective period for application is in spring when the oxalis is growing actively and vigorously. Be prepared for some re-growth later in the season or the following spring, which will need a repeat application of weedkiller. Protect grass and garden plants from accidental spray drift, or apply glyphosate specifically to the leaves of the oxalis. 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.
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 home gardeners (Adobe Acrobat pdf document outlining weedkillers available to gardeners; see section 4)
Chemicals: using safely and effectively
Chemicals: using a sprayer
Chemicals: using spot and broad-scale weedkillers
Weeds: non-chemical control