Weedy oxalis

Christiaan van Schalkwyk cvschalkwyk@lantic.net
Wed, 24 Nov 2010 06:56:21 PST
Hi All

In my nice South African garden Oxalis convexula has never formed axial 
bulbs. But some other species do. Salter in his monograph noted that O 
convexula is such a vigorous plant, that it kept growing inbetween the pages 
of his press, he had to poison it in order to make herbarium specimens.

One needs to remember that most Oxalis species will not form seeds in 
cultivation, with the exemption of much collected species, such as O obtusa, 
O purpurea, O flava, O hirta, and possibly O ambigua (there might be more - 
but that's all I can think of at the moment!). Even O pes-caprae does not 
set seeds, it is the bulbils thats causing all the problems.

I have planted many Oxalis in my garden, which gets water weekly throughout 
the year. O. obtusa did not survive. Different forms of O flava, O purpurea 
as well as O stenorrhyncha, O adenodes, O annae, O gracilis and O convexula 
looked very stunning this year (the 2nd year) Some bulbs were removed 
(garden rearrangement ! ) and were definitely more abundand, but did not 
spread much wider that where they were orriginally, with the exeption of the 
white flowered form of O purpurea, which sent up a tuft about 30cm from the 
mother plant.

Mostly I would recommend pot culture, as it is still the safest way to grow 
Oxalis. But the pots should not sit on the ground - the drainage holes are 
excelent for escapee bulbs to form and spread. The only species I can regard 
as being invasive in my garden is O zeekoevleyensis (I had (HAD!) two 
different clones and they did set seeds abundantly) and O haedulipes - once 
again too many colections thus more than one stylar form + being in the 
centre of it's natural distribution + the necessary insect vectors = seeds. 
Even with more than 70 forms of O obtusa and deliberate pollination, I very 
seldom see seeds on this species. The other invasive Oxalis species are 
Oxalis corniculata (non bulbous, and set seeds easily) and O latifolia, an 
invasive weed from North America.

Happy growing !

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