Plant identification
Question from Charlie:
I am trying to identify a small bulb that I thought was cute when it first arrived in the soil of another plant. Now I think it is a weed – very prolific. I suspect it is in the oxalis family: 3 lobed leaf, red stem, pretty pink flower that is petunia-like & about 3″ tall, but lays on the ground. It has taken over my garden & I’m trying to dig it out. It starts as a seed & becomes a bulb. Can you confirm my suspicions? Any suggestions on getting rid of this plant? (I looked under oxalis in my Western Garden Book & didn’t find any that matched my plant.) Will Roundup kill it?
Answer from Pat:
The small, winter-blooming, pink flower with yellow eye, and three-lobed, grayish-green foliage is Oxalis purpurea ‘Cherry’, a selection of a South African corm. This dwarf, ground-hugging variety you have is somewhat rare. However, the surprising fact is that I have it in my garden also where it is often admired and where I cherish it myself. There are many other named cultivars of this species of oxalis but you have one of the rarer types. I’m surprised you don’t like it, but I imagine the difference is how it is being used and whether it gets inadvertently moved around. I have it growing on the edge of a raised bed that is walled with un-mortared stone. For the most part it stays close to the rocks and graces one side of a path. In this area, it’s neat and tidy looking. The foliage springs up with the first rain and is soon dotted with flowers that bloom in a cheerful shade of deep pink all winter long. As soon as hot weather returns it dies to the ground and is not seen again until fall. The color of the flowers looks particularly good inside each individual plant’s rosette of soft gray-green foliage. So far as I can tell this oxalis has no pests nor diseases. Caterpillars, slugs and snails all shun it.
You mention the fact that for you it is invasive. If one digs up the ground in the area where it is growing one might spread the corms. That has happened in my garden and a few of these plants are now growing in a wildflower bed in my garden, but they are as welcome there as they were in the other location. I don’t think this plant makes seeds, and in my garden it stayed in one place for many years and actually took many years before I had enough of them to share with my friends who wanted some. Maybe you are being too good to it?
If you really want to kill this oxalis I suppose Roundup would do the job, but I am not sure, since the corm might continue to live—corms tend to be persistent—, and anyway, as an organic gardener I don’t believe in Roundup. If you used Roundup you will find that seeds will not germinate well for several years in that area. Here are three ways for getting rid of it: One: You might be able to ask your local garden club to come and dig these plants up and pot them for one of their garden sales since it’s much admired by many gardeners and difficult to find. Two: I would think that the best way to get rid of this plant would be too dig them up during growth and bloom and sieve the soil, throwing away the corms. Start digging them up in fall and continue until spring, getting rid of the plants each time a new one sprouts. Three: Shade kills this plant. Cover the ground with a thick layer of mulch and you will not have it any more. I think the reason my little patch of this oxalis never spread is because I habitually mulch the ground. The only place it could survive was in the earth-filled crevasses of a dry wall.
Thank you. I will go take a better look to see if it matches the picture that you sent. I’ve never seen any seeds, but it has spread so far that it has to be the birds spreading it. It went from my back yard to the front & it’s in the grass. Also, when I do dig them up (I haven’t used the Roundup as it has woven itself throughout my other plants), many just go straight down, with no bulb, but others, with a little more root, have the start of a bulb. Older ones have a bulb that is dark brown & oval – they look like little footballs. As I said, when I first got it, I too thought it was very pretty. But this past year it has gone crazy & invaded many beds – anywhere there was an ounce of bare soil. It does die down once the hotter days arrive. Now I can’t wait to check it out, as I don’t remember the yellow throat or the darker color near the throat. Does the cherry oxalis have a red stem?
Where do you live? There is a pink oxalis that is widely grown in Texas. It has dark stems and is known to be a bit weedy and spread all over the garden. Also, it has more than one flower per stem. My type of oxalis has only one flower per stem. I went down into the garden and looked at the stems of my oxalis and no they are not red. They are green, so perhaps you have another species, one that is far weedier than what I have and that spreads by seeds. Mine is probably a hybrid variety that only spreads by corms or possibly by bits of root. I may have more of these plants this year than other years but the ones that have spread were the result of digging, not seeds spread by birds. This particular species of oxalis that I have does not make seed pods, nor does it attract birds nor bees nor any other insects who might pollinate it. What climate zone are you in? This also can affect the ability of a plant to spread by seeds, since soil temperatures are key to seed germination. Some seeds fail to germinate in my garden because temperatures don’t drop low enough to trigger germination. You may have Oxalis ‘Grand Duchess’. It is taller than what I have and somewhat more invasive—though folks say never weedy—but it will grow in partial shade better than my pink hybrid oxalis. The pink Oxalis purpurea ‘Grand Duchess’ looks almost identical to what I have but the flowers are larger and petals longer. I used to grow a white cultivar of ‘Grand Duchess’ but my gardener pulled it all up one time when I asked him to pull the weeds that were mixed into it. He thought I meant pull up everything. Anyway, it never came back so I think you could get rid of this by repeatedly pulling and digging up the corms.
I live in Lakeside, climate zone 21 I think (same as the citrus in Western Garden Book), or zone 9, depending on the scale you use. Quite cold (for here) in the winter & hot summers. I only have one flower per stem, but like your idea of sifting the soil to get the bulbs. I also think this is going to be a dig it up project, but wanted to know just what I had. I do have a white oxalis in my yard, although I planted it in the shade. It doesn’t seem to be prolific like the other one.
Thanks so much,
You’re welcome. Good luck with sifting the soil and getting rid of the corms. If you keep at it, it will work.