Oxalis is the generic name for a large group of flowering plants, of which many species are commonly known as wood sorrel, or yellow or pink sorrel.
Originating from regions such as South America and southern Africa, many oxalis species are hardy enough to survive in this country’s climate. Several are grown as ornamental plants, as their clover-like foliage and pink or yellow flowers are certainly attractive - but some species can become hard to control and pests in the garden.
Here's everything you need to know about Oxalis.
What do oxalis plants look like?
All oxalis have three-part, clover-like leaves; in fact, one common name for some species is false shamrock. Oxalis corniculata (below) has a creeping stem, small yellow flowers and upright seed capsules; there’s also a purple-leaved variant.
The tropical American Oxalis debilis has deep pink flowers from July to September; Oxalis latifolia has the same flower, but from May to September. The latter species has particularly broad leaves, with triangular leaflets, making it easily distinguishable from others.
How does oxalis spread?
Oxalis spreads via seeds, or bulbils - small bulb-like structure on the leaf, which fall easily to form a new plant. In Oxalis corniculata, an annual, the main means of spread is by seed, ejected from its ripe seed pods.
Most of the other perennial species, including Oxalis debilis, rarely produce seeds but their bulbils, attached to the parent plant, are easily spread when digging and can remain dormant in the soil for several years. Oxalis latifolia reproduces both by seed and by bulbils.
How do I kill off oxalis?
You can kill off oxalis using non-chemical means; try digging out Oxalis corniculata in particular, or suppressing it with mulch.
A tough raking regime in mid-September can help shift most of this weed, but in particularly difficult cases you may need to strip the turf and re-seed in the spring or autumn. Repeated hoeing can help kill it in herbaceous borders.
In the cases of Oxalis debilis and Oxalis latifolia, try forking out the weeds in spring when the bulbils are still developing and are firmly attached to the plant - later in the year they will come off easily and cause the weed to spread further around the garden.
In shrub borders, apply a heavy leaf mulch and keep it topped up to ensure the oxalis stays buried – you may have to continue mulching the area over a number of years.
If you have to resort to weedkiller, you should choose a glyphosate-based product which shouldn’t stay in the soil too long, but will kill any other plant it touches, so take care – and don’t use it if rain is forecast.
Unfortunately Oxalis corniculata is fairly resistant to most domestic weedkillers, so spray directly in spring, but be prepared to have to re-apply later in the year.