Monday, December 20, 2010

Oxalis, how I loathe thee

I’ve heard people say that weeds are just unloved flowers; plants whose virtues have not yet been discovered; or perennials that haven’t been educated yet.

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Common yellow oxalis sprouting with abandon
in our succulent bed

I don’t agree. What I do agree with is the Danish proverb “Weeds never die”. When everything else is on the wane, weeds are busy laying the groundwork for next year’s invasion.

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Oxalis growing between the stems of a sea urchin sedum
(Sedum lineare ‘Variegatum’)

My biggest enemy in the realm of weeds is oxalis, or wood sorrel. There are many oxalis species grown as ornamentals, and yes, they can be beautiful. The one I’m having a beef with is the common yellow wood sorrel (Oxalis stricta). It grows everywhere and at any time of year—the photos in this post were taken just now, a few days before Christmas—and it seems to prefer places where I would have to sacrifice skin and blood to get to it, like the base of prickly succulents. It prefers alkaline soil, which is pretty much all we have, and it loves the sun, of which we have plenty as well. Its roots go straight down and its stems are weak, making it impossible to pull out neatly. If you leave any of the root behind, the plant will happily make a comeback.

Roundup (glyphosate) is an effective weapon, but for every oxalis you kill, ten more are waiting in the wings—and it’s all to easy to damage desirable plants growing nearby. Plus, the environmental impact of herbicides is something that does concern me, so I only use Roundup when I absolutely have to.

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Newly sprouted oxalis at the base of a potted Bambusa dolichomerithalla 'Silverstripe'. This is fresh soil that we had brought in a month ago; I doubt that the oxalis seed was in the soil. It somehow landed on the soil after I potted up this bamboo.

So, what to do about this noxious devil with the pretty yellow flowers? I’ve read of people using the wand of a steam cleaner to literally cook weeds in situ. I was going to give this a try but our steam cleaner is for mopping floors only and doesn’t come with a wand. If any of you have successfully employed this method, please let me know. I like the idea of it, but I’m not entirely convinced that it would destroy the roots of oxalis, too, and unless you kill those, the leaves will grow back in a hurry.

Another solution I’ve heard about is using a portable flame thrower, or “weeding torch”, that public works departments often use for weed suppression in parks. While I don’t have one of those, I do have a chef’s torch—the kind you use to caramelize sugar on top of crème brûlée. Being the curious mind that I am, I decided to give it a try.

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My trusty chef’s torch, never used for anything this crude
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Chef’s torch in action—will the oxalis survive the blaze?
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Before…
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…and after

The chef’s torch certainly worked. It burned the oxalis to a crisp in a matter of seconds, creating a pretty nasty smell in the process. Since our succulent bed is criss-crossed by drip lines, I had to be careful not to get too close. That severely limits the usefulness of the chef’s torch, or any other fire-spewing implement, in this bed and all others that are on a drip system.

But this was just a quick experiment anyway. I’ll keep a close eye on the areas that I torched to see if the oxalis will come back. I have no idea how deep into the ground the heat penetrated so I don’t know if the roots are dead or alive.

To get rid of the rest of the oxalis, I’ll resort to my tried-and-true methods. Old-fashioned weeding implements work, at least in easily accessible places. Smothering the seedlings with newspaper plus a layer of mulch does the trick as well. And as last resort there’s always a well-placed squirt of Roundup for the areas that I just can’t get to easily, combined with a quick plea for forgiveness from Mother Nature. But no matter how many minor battles you walk away from victoriously, it seems that you simply cannot win the war against oxalis.

6 comments:

  1. Ah, we cold-climate gardeners have a little advantage here: there are a few months where we don't see the wood sorrel, or at least don't care about it. =)
    .
    I wouldn't say this is my worst weed, but it's one of the contenders. I have one bed in particular that the sorrel has invaded, and it's a never-ending battle. I think pre-emergents like corn meal gluten help somewhat.
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    The only thing good about wood sorrel is the sour-tasting stems.

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  2. Oxalis is everywhere in our garden. It has a nasty habit of getting intertwined with desirable plants so it's pretty much impossible to eradicate. That's what I want to be more diligent now as the seedlings come up.

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  3. Oxalis is an irritating weed here too. I find it an enigma, in that as you've said, they tend to appear more on the bases of plants and places where it's tricky to reach without getting pricked and scratched. Difficult to totally get rid of.

    I refer to it as 'Nursery's favourite freebie' too, unfortunately they come in 'free' together with the plants you buys, especially palms and agaves :)

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  4. Mark, I love what you call it, "favourite freebie". That's so true. When I planted the bamboos in our horse troughs, every plant had a bunch of oxalis growing in it. I'm sure I didn't get it all out and soon there'll be whole colonies invading these troughs.

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  5. Hi Gerhard, this is the most frustrating weed for sure. We are professional gardeners, and every landscape is infested with this stuff no matter the frequency of weeding or spraying. Sigh. As an alternative to flaming, you can also try the organic herbicide "Burnout" but it only top-kills and you have to protect other plants. Good luck!

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  6. Thank you for the recommendation. I'll check out Burnout for sure. The two small areas I'd flamed with my kitchen blowtorch have already grown back--if not from the roots of the plants I thought I'd destroyed, then from freshly sprouted seeds.

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