Acceptable Oxalis

Ron Vanderhoff
Wed, 29 Apr 2009 21:12:18 PDT
Nice discussion. Invasiveness is a variable measurement. By the same definition many common groundcover plants could be considered "invasive" - Hedera, Vinca, Gaultheria, Lonicera, Pachysandra, etc. It's all relative.
Yes, Oxalis obtusa can colonize are area of a garden, especially in mild climates like ours in California. Soil texture seems to have a great deal to do with the speed of colonization of species like Oxalis obtusa. In loose, sandy soils, such as that of a plunge bed or in containers many species of plants spread underground rather quickly. Those same species, when in a garden environment with heavier soils, will expand much more slowly.
Another form of dispersal and "invasiveness" that some of the most troublesome South African Oxalis employ is to produce aerial bulbils. These above ground miniature bulbs are usually developed in the leaf axils of the parent plant. They are often produced by the hundreds, even thousands, especially on South African species like Oxalis inaequalis, fergusoniae and convexula. As the plant desiccates, the bulbils are detached and, because of their tiny size, are easily dispersed. It is interesting that the species that produce big quantities of aerial bulbils also have very short underground rhizomes. They rely on above ground dispersal, rather than below ground.
In my collection I find these the most dangerous of the Oxalis species and they can get out of hand very, very quickly in a collection or in a mild climate garden, even if grown in very secure pots. Fortunately, these species are not terribly common in collections or gardens.
 Ron Vanderhoff

From: Michael Mace <>
Sent: Wednesday, April 29, 2009 3:30:40 PM
Subject: Re: [pbs] Acceptable Oxalis

Jane wrote:

>> O. obtusa in a warm pink hue. It IS an invasive one, swarming around in
the plunge sand among the pots

I can definitely picture O. obtusa being invasive in plunge media.  In pots,
some of them multiple explosively for me.  But in the ground I've found that
it not only doesn't spread, but tends to fade away over time in my part of

Two things seem to limit its growth:

--Unlike O. pes-caprae, it doesn't grow taller when there's competition.  So
the annual grass that dominates in California seems to choke it out.

--California's rodents love, love, love to eat Oxalis obtusa.  I would have
lost all of mine if in pots if I didn't embed chicken wire in the top of the

Have other folks found that O. obtusa is invasive in the garden?


San Jose, CA (min temp 20F) 

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