Plant Doctor Archive

Combating oxalis

I HAVE a nasty weed rampant in my garden - oxalis - which has a white flower. The bulbs are covered in little bulblets that pop off into the dirt as you dig them up and they spread even more. I have managed to keep some areas at bay by smothering them with newspaper and bark, but it is incredible how far they will creep. The worst place it occurs is in the vegetable patch where it has spread through compost. If hoed over, it just pops up again the next day. My elderly neighbour has told me he got rid of his by dabbing the leaves with creosote which burnt the bulbs. As I can't imagine this would do the soil any good, I was hoping you could make another suggestion.

THERE are several types of oxalis that can be a nuisance once they get established. It sounds as if your problem is probably Oxalis incarnata, though its flower tends to be pale lilac rather than white. However, control is the same regardless of type.

Probably the easiest way is to use one of the many glyphosate-based weedkillers on the market, such as Roundup, Glyphosate 360 or the convenient ready-touse types like Zero or Weedmaster Blue that come in trigger packs and need no mixing. The active ingredient (glyphosate) is absorbed through the leaves and travels through the plant to the bulbs, killing them, as long as enough of the product is absorbed.

Apply the first spray when there's a lot of oxalis foliage present to absorb the active ingredient, then spot-spray regrowth regularly as it appears. If you're vigilant you should reduce the problem, but it can take time and patience.

Glyphosate breaks down in the soil and doesn't affect nearby plants, as long as you don't get it on their foliage or stems.

Another product effective against oxalis is Escort, but it's generally more expensive and less widely available than glyphosate.

Reproduced with permission from the former Weekend Gardener magazine. The views expressed here are not necessarily those of the RNZIH.