Oxalis has small, pale green clover-like leaves made up of three heart-shaped leaflets. Flowers vary in colour from white, yellow and pink to red. Clusters of leaves grow from finger length to hand length in height and form mounded rosettes.
There are a wide variety of Oxalis species and many of them can be problem plants in our gardens. Low growing Oxalis is more of a nuisance than anything else. If allowed to get out of control, it can form a dense carpet of foliage that suppresses the growth of other plants. This would make it a particular problem in a permanent planting like an asparagus patch. Oxalis doesn’t attack and trample neighbouring plants but it does compete for essential nutrients and it is very persistent and invasive thanks to a few clever tricks.
Oxalis spreads by seed as well as small bulbils that develop from the roots. When you come across the clover-like foliage in your garden and yank it out of the ground by hand this releases a parent bulb and numerous smaller bulbils in the soil below. All of these will simply grow on unhindered. If you are digging through a bed and you dig up Oxalis plants to remove foliage then the small parent bulb and even smaller bulbils will be even happier as they are hard to see and most often get freely distributed through your soil to grow into even more plants.
Controlling Oxalis without the use of chemicals takes time and patience. You can certainly make a difference and reduce the quantity of Oxalis present in your soil – even if you end up learning to tolerate it over time.
Remove all foliage whenever you see it. This will weaken plants considerably over time and help to prevent re-growth. The aim is to be even more persistent than Oxalis itself and to keep depriving it of its ability to nourish its bulbs hidden in the soil below.
A similar method of foliage control is to drench leaves and immediate surrounding area with the following mixture:
2 tablespoons of baking soda
1 squirt of washing up liquid
Spray the solution onto foliage – ideally on a hot dry day for the best effect. Repeat whenever new leaves appear and continue to apply until no more re-growth occurs.
I dig up Oxalis whenever I come across it, carefully lifting each plant with the soil that surrounds its roots. I then sift through the soil around the roots and locate the parent bulb and smaller bulbils. It is important to dispose of the bulbs in a way that stops them re-entering your garden or compost heap where they will simply re-grow as new plants. Crushing them on hard paving seems to work well. This might seem painstaking but it is worth the effort and does greatly reduce the amount of Oxalis in a vegetable garden where it is present.