If you’ve noticed small, clover-like weeds with heart-shaped leaves spreading across your lawn, you’re likely dealing with Soursob (Oxalis pes-caprae). These persistent little weeds are one of the most common challenges homeowners face, and unfortunately, they can’t be conquered with a quick spray-and-forget approach.
Make sure you don’t confuse these with clover or creeping oxalis – they look similar but grow differently and therefore treatments for clover and creeping oxalis will not work on your soursob.
Identifying Soursob
Soursobs are regularly confused with creeping Oxalis due to their very similar leaf appearance. Soursobs spread with large heart shaped leaves along the ground, producing flowers with 5 petals and have a long white tuberous root.
Cooler conditions are when Soursobs like to appear in Autumn and Winter, specifically June to October here in South Australia. The problem with Soursobs is that they are extremely resilient to herbicides and have a fast-growing system of onion like bulbs growing beneath the surface.
In addition to this, they have small secondary bulbs known as bulbils. These bulbils are attached to the root system and each Soursob can have as many as 20 bulbils! When you remove the plant, the bulbils are left behind that then detach and grow into a new plant and the cycle continues.
One of the most important things to do is to try and target Soursob before it flowers. It is when it is flowering that the bulbils are growing and creating more plants.
Why Traditional Herbicides Fall Short
Due to the extensive bulbing growing system, Soursob can’t be controlled with your standard herbicides. They may temporarily burn off the visible top growth of Soursobs however they won’t touch the bulb system underground and therefore their way to regrow and spread.
The result? The weeds keep coming back because the bulb remains intact and ready to produce new growth.
How to tackle a Soursob infestation
Completely eradicating Soursobs from your lawn will take a bit of time and effort. Unlike many other weeds, it is not recommended to remove them by hand, as the bulbils will break off and continue to grow beneath the soil allowing it to reappear. There are also no selective herbicides readily available for domestic lawns that will target the Soursobs, so you will need to take a few other steps to try and remove it.
Mowing them off regularly will weaken the plant helping your grass to overcome the infestation. Bulb exhaustion occurs just before flowering, so this is the perfect time to implement your mowing and non-selective herbicide application, when the plant is weak. This is the only stage that physical removal will be an option, by digging up under the plant and removing the soil around it as well.
You will be able to tell the plant is at the exhaustion stage if you carefully dig up a plant – the adult bulb will be shrivelled and the root under the bulb won’t have grown yet or is extremely young and thin. Spot spraying carefully or using a weed wand with an application of Glyphosate (Round Up or Zero) will be your best course of action, but you must be careful when applying as it will kill your turf as well. Acting quickly will also help you to stop them in their tracks before they produce more bulbils.
Soursob are prolific (over 1.2 million hectares in SA are infested), but with some patience and regular mowing you can tackle them head on.
