Flowering Oxalis
Mary Sue Ittner (Fri, 20 Nov 2015 08:37:12 PST)

Note to those who care, in my response I'm going to use bloom and
flower as synonyms in this post.

I got hooked on Oxalis a long time ago and found a few things that
have contributed to growing and flowering a number of them. I have
the best luck with the ones that bloom in fall, but also Oxalis
purpurea and Oxalis obtusa have long periods of bloom. I suspect we
all have different experiences and since they grow in different areas
of South Africa with different conditions probably there is no advice
that works for all of them. You will no doubt get different advice
from different people.

I usually repot them every year and share the smaller ones with the
BX. I remember how generous some of you were sharing yours with me
and pay it forward. A few species are in my raised beds that are in
pots, nestled in pots, and those don't get repotted very often. A few
species disappeared with this treatment, but a few others have been
very successful left alone. One of the Oxalis luteola forms blooms a
long time every year and for the first time this year Oxalis
palmifrons bloomed in my raised beds. That was exciting as it had
never bloomed before when I repotted it every year so perhaps not
being disturbed may have been to its liking. Who knows.

The ones I'm going to repot I leave in paper bags once I unpot them.
I open the bags every now and then and when I see signs of activity I
pot them up and water them. This is usually in August. Some of them
can start blooming in August or September. Fall blooming is perfect
for my climate since it hasn't started to rain yet and we have less
fog. Unless there is sun and warm temperatures the flowers don't
always open. Many of the species I grow do better in deeper pots.
Oxalis melanosticta 'Ken Aslet' was a shy bloomer until I started
potting it in a deeper pot. This year the first flowers appeared in
August and new ones continued into October.

Others with three to four months of flowering this year starting in
August to September and some still going strong: O. commutata, O.
hirta, O. pardalis, O. imbricata, O. bowiei, Oxalis pulchella v.
tomentosa, O. peridicaria, O. zeekoevleyensis, O. versicolor, O.
engleriana, O. assinia, O. caprina. O. massoniana, O. depressa.

Others bloomed for only a couple of months, but that is still more
satisfying than days or weeks as is the case for some of the other
bulbs I grow. O. bifurca, O. callosa are two in this category. Other
species start to bloom later like Oxalis luteola and O. compressa,
but may last for many months (five months for O. compressa last
year). If it starts raining a lot, some of them are done, but others
like O. purpurea continue. Last year when we had two "atmospheric
rivers" I had some serious problems with many of the species that got
such heavy rain so plan to shelter them from a lot of rain if we get
it this year as predicted. Some years I've put the pots in a cold
frame and closed it when we got a lot of rain. I grow several forms
of O. flava and some do better than others (one to three months of
flowers in the fall). O. polyphylla is not in flower for me as long
as other species and O. glabra is a bit weedy so I don't have a pot
of it anymore although it is appearing in other pots and usually
flowers later. O. obtusa starts later (December to February and lasts
until March).

You should look in the archives as there is a lot of information. For
instance there was a Topic of the Week on Oxalis with this introduction.
http://pacificbulbsociety.org/pbslist/…

Also Mike Mace wrote about his experiences:
http://pacificbulbsociety.org/pbslist/…

Sorry this is so long, but hope it helps. I think Southern California
is ideal for growing these and as you go farther north it is probably
more challenging. In our four years of drought I think they have been happier.

Mary Sue

Mary Sue Ittner
California's North Coast
Wet mild winters with occasional frost
Dry mild summers