Saturday, July 24, 2010

A Horrid Weed... Oxalis!

"Oxalis? Any magic cure for this horrid weed?"  Jane

By chance the subject of Oxalis came up as I joined a gardening forum at Burnley Gardens last Sunday.  I was lucky enough to hide behind those more knowledgeable and absorb information that turned out to be immediately valuable.

Oxalis is not a weed that causes nursery problems.  We are troubled more by the annuals that spread quickly by seed, Flick weed, willow herb and chick weed.

This is a form of flick weed, a type of mustard that flings seed far and wide once the seed pods have matured. Comes up like hair on a cat's back if we don't maintain our hygiene.

Oxalis is particularly horrid in gardens because it's an herbaceous perennial with a tiny bulb that lurks deep under the soil surface waiting for the opportunity to sprout.  The bulb is designed to protect the plant and that's why is it so successful. You can quite easily remove the top of the plant but it's near impossible to get at the bulb, especially once it has established. And they multiply!

The usual response to Oxalis is RoundUp (Glyphosate), I think most gardeners are aware of RoundUp or Zero.  It has been around a while now and it's very effective and apparently safe.  It works by interrupting the photosynthesis process (that's why they say it can't hurt us, we don't photosynthesize) which should starve the plant, roots and all.  Because the Oxalis bulb stores energy for the plant you might need a few goes to kill the bulb.

Most gardeners I know prefer not to use chemicals so the question becomes how do you control Oxalis without spraying.  My grandfather used to get me to dig them up from the formal beds at his home.  Very carefully digging down to find all the bulbs. The soil was well worked so the digging wasn't too difficult, but that's just the environment Oxalis loves. The agreed solution at the Burnley College forum was to crowd the weeds out with mulch.  Heavy mulch. Try a layer of cardboard, newspaper or even carpet underlay under a more regular and attractive mulch to force the weeds to stretch too far to find a path to light. The alternative was a really thick ground covering plant like Myoporum parvifolium (I have to say I'm sure I've seen Oxalis bursting out from this type of ground cover so layering all these various mulches sounds the best option).  I'm honestly not sure if the bulbs eventually starve under all the mulch or how long it would take to happen. Still, I'm a big fan of mulching... although that lead to another discussion over the merit of mulching in fire prone areas.  Best leave that for another day.


  1. Hi Peter we dig ours up, over time they stop coming back but it does take a while!

  2. These are a type of yam. EAT the bulbs!

  3. Oxalis is toxic, don't eat.


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