Trading weeds

Thu, 07 Feb 2013 10:48:34 PST
The spread of Oxalis that do not set seeds can be put to carelessness. With
regard to O. pes-caprae, one could say that most of California has been
horticulturally careless, even though this is a beautiful and unique
species with a distinct floral fragrance.  Contained in pots there should
be no problems controlling their spread. I recommend an austere regimen of
mineral soil (mostly sand), very little fertilizer and full sun. From my
experience growing many dozens of accessions of Oxalis, I found there are
two basic requirements for seed production: pollinators and multiple clones
(or species that will cross). Most species seem to be self-incompatible.

Oxalis that set seed are usually obvious because the flower stalk is firm
and even a little taller after the flower wilts. Unfertilized flowers
wither quickly. The young fruits can be pinched off before they distribute
their seeds but it is easy to miss a few and end up with volunteer
seedlings. This can be a nightmare but also can result in some very nice
chance hybrids. If you are growing more than one form of, say O. obtusa,
then it can be a challenge to keep them "pure" over time.

Oxalis is an extraordinarily diverse genus with bulbous, tuberous and
fibrous-rooted species. Off-hand I cannot think of another genus of
geophytes that exhibits both bulbs and tubers. Some produce rosettes of
beautiful foliage for many years before they offset (if they ever do) and
never set seed. Others that make rice grain bulblets can be a real menace
and should not be promoted. It might be worthwhile to designate on the Wiki
those species that are known to be weedy.


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