Oxalis Eradication

It is the Winter Solstice in the Southern Hemisphere and the yellow-flowered weed Oxalis pes-caprae is beginning to flower in our local parks and reserves. You will want to stop this weed in its tracks if you have it in your garden or  native wildlife reserve. 
 Oxalis is not an easy plant to suppress because, as well as spreading by seed, it produces tiny underground bulbs that break off when you pull out the plant.

 Early to mid-winter is an ideal time to tackle Oxalis. One person can do this alone in a domestic garden but in a park or reserve it is better to divide up the area into bight-sized pieces and share the load between a group of volunteers. I am experimenting with the following method of weeding a small area near the bridge in Newell's Paddock Urban Park. If successful, this method might work for our Friends of N. P. and other volunteer groups:




 Seven Step Glysophate-free Method of Controlling Oxalis
1. Concentrate on thoroughly eradicating a small area to begin with. Choose a site that is easy to access and that you will enjoy intensively weeding. If you have a large area of Oxalis it will be impossible to clear the entire infestation in one season. Choose a small area (no more than 2 sq. meters per person) to intensively weed by hand but don't ignore the remaining infested areas. Hand-weeding Oxalis will take several years and requires commitment. I weed my special site for ten or fifteen minutes once or twice a week, combining it with dog walking. I always keep my chosen hand-tools- a two pronged weeder and an old bread knife- plus an extra plastic bag in my dog-walking kit.

2. Avoid disturbing the soil. Remove Oxalis plants as early in their growth stage as possible by digging out the plants using a small hand-tool. If the Oxalis is coming up through another plant, try easing it out using a screw driver or knife so as not to disturb the roots of the plant you want to keep.
Alternative safe chemical method: In a small spray bottle, mix 4 teaspoons of Baking Soda to a litre of warm water, add some washing up detergent and shake. Squirt a dose of this mixture directly onto the leaves of individual Oxalis plants on a dry, sunny day. I haven't tried this yet but a combination of both methods might be a good approach. Be prepared to repeat this process throughout the winter growing season. Repeat the process diligently next winter as many Oxalis bulbs will remain in the ground. Eventually, without leaves, they will run out of energy.

3. Don't infest another area*. Dispose of dug-up Oxalis plants by placing them in a plastic bag, sealing it and leaving it in a sunny place to sol-anise (cook). I wait until I have filled a plastic shopping bag with weeds before I place it on the roof of the shed at home for a couple of weeks before putting the bag in our landfill garbage bin.

4. Nature abhors a vacuum. Plant to replace the weeds in the area you have intensely weeded. Aim to smother or out-compete weeds with local ground-covers. Seek out suppliers of local indigenous ground covers. Salt bushes are the first line of defense, then Poa, Dianella and Lomandra species. In a bush-land garden or wildlife reserve, observe to see if indigenous plants spontaneously appear.

5. Nip it in the bud. It is important to remove all the buds and flowers of Oxalis growing within a radius of at least 5 meters from your intensely weeded site. Using garden shears or a bread knife, cut off the flowers and seal them in a plastic bag*. As you finish completely clearing one small area you can begin to expand into the surrounding areas. The seed pods of Oxalis burst, releasing hundreds of tiny seeds that can be dispersed by the wind, enabling thousands of Oxalis plants to reappear next year, including in the area you have already spent hours intensively weeding. 

6. Mulch the surrounding area. Aim for a layer about 750 mm deep. Each Oxalis plant has a fleshy tap root to store energy to tide it over to the next season. Oxalis will break through a thin mulch. Oxalis seeds can germinate in thick mulch but at least seedlings will be easier to pull out!
 
7.  Be prepared to persist for at least three years. Expand your intensely-weeded zone next year and in the years following. Revisit and deal with any Oxalis outbreaks in your original intensively weeded area.