Acceptable Oxalis

Most of the winter growing south african species of Oxalis should be quite
winter hardy. Some beautiful species and forms are found in the vicinity of
Sutherland, which is regarded as the coldest place in South Africa, with
daytime (winter) temperatures often below 5 degrees Celsius, and night
temperatures well below zero(up to -15 !). (Over the whole year an average
low of 3 degrees, and an average high of 20.5, according to
http://www.sutherlandinfo.co.za/).

It must be remembered that very few Oxalis in cultivation will produce
seeds, as it is not self fertile. However, when large quantities of various
clones or collections of the same or similar species are cultivated, seeds
might be produced. This could happen with Oxalis obtusa, the Oxalis
flava/fabaefolia group, O. purpurea, O. luteola, etc., of which many
different forms have been collected and are available. So if only one clone
is grown no seeds will be produced - this is true even for Oxalis
pes-caprae! (this, however, is not true of the weedy Oxalis of the
America's - but then they are mostly annuals, and do not produce bulbs).

All the "spreading" and "invasiveness" of (South african) bulbous Oxalis is
thus more due vegetative reproduction, and if Oxalis are kept in a pot, this
should keep the species where you want it to be. I say should, becouse
Oxalis roots can grow very deep, and if the pot is placed directly on (or
in) a suitable growing medium, the roots can go through the holes in the pot
and into the soil, and voila ! an escapee ! - most probably this is the
source of Jane's plants in the plunge sand.

Most Oxalis renew their bulbs each year, and various different forms of
vegetative structures (stolons, rhizomes, runners, etc.) are formed, along
which bulbs can develop. Species with these structures are more invasive
than those who just quietly multiply where they are. Oxalis lawsonii (which
is a spectacular species) is reported to produce bulbs up to a metre from
the orriginal bulb in a single season. Many forms (not all!) of O purpurea
(and similar sp.) do not form these structures, and will multiply locally,
but do not spread as much or as quickly.

Unfortunately the underground system of Oxalis is not well studied, and the
info that's available are not easily accessable. The easiest method to test
an Oxalis' ability to spread is to plant a single bulb in a large pot, and
check it the second year to see where all the new plants pop up in the pot.
If it is in the centre (where the orriginal bulb was planted) it is not
aggresive, if plants pop up all over the place underground runners or
stolons have been produced, and the species are thus more aggresive.

And luckily most unwanted Oxalis succumb to a single touch of a brush dipped
in a systemic herbacide . . .

Christiaan

----- Original Message -----
From: "Lauw de Jager" <contact@bulbargence.com>
To: "Pacific Bulb Society" <pbs@lists.ibiblio.org>
Sent: Tuesday, April 28, 2009 10:24 PM
Subject: Re: [pbs] Acceptable Oxalis

Dear all,
It is very hard to overcome the prejudice against Oxalis. I offer about 15
species and forms and try to be very careful not to offer species which can
spread dangerously.