I'm sorry, I dont have much to contribute but I'd also like to hear from people that grow it! My mother brought me home two little baggies of 'Iron Cross' bulbs and I simply planted them like the directions said without any special treatment and nothings happening...best way to get these going? I also tried a pot of them in the unheated mini greenhouse to see if the cold from winter will help them come up in spring....
~Michael

I cannot help with the hardiness issue, but I do know that they are not invasive, unlike others of their tribe.
Here in the Mediterranean, we have a massive problem with the South African Oxalis pes-caprea. It has taken over the entire island of Crete.
When I moved in to this little house, I waited a whole year before planting to make sure I had eradicated all of it from my garden. Huh... I need not have bothered. It has seeded back in from the surrounding area and is now a nightmare.

My daughter sent me a mixed box of bulbs from England last September including Oxalis Iron Cross.
It is strange, but even though I know that they are not invasive, I cannot bring myself to plant them in the garden.
I planted some in pots and they were up and flowering by November. They are lovely, very pretty. Now they have finished flowering, I am looking at the pots of very attractive foliage, wondering what to do with them.
I still cannot bring myself to plant them out in the garden.
Completely irrational I know.
Daisy

I also planted them in zone 6b to 7a, and they didn't overwinter.

-Daisy, I feel your angst in planting other oxalis. Over here O. corniculata is a real pest. Last year I was kind of tempted by an O. rosea offered at a local plant sale, but chickened out. LOL.

-dbarron, thank you for your comment on hardiness! I was a little suspicious of my catalog hardiness rating....
CMK

They have overwintered here for maybe 10 years & multiplied somewhat, not aggressively. I will be looking for them this spring, our temps have gotten below 0 several times this year. We've been in the single digits since they have been planted, & there was a reduced number of them the following year, this might be the year they don't come back.

-ngraham, appreciate the info. Do you have yours in a sheltered or open situation? If you have the time, would you maybe post again come spring and let us know if they survived?
CMK

I'll try & remember to let you know. They are always late to show up, so will be a while, I'm thinking late May. If I forget, you might shoot me an email to remind me. I have several different varieties, none have been aggressive for me, & a couple I don't expect to return this spring. Mine are fairly close to my house, but on the north side & unprotected by shrubs or larger plants.

-ngraham, many thanks! ;-)
CMK

Sorry to be so late in my reply. I had 4 different varieties of oxalis, including Iron Cross. Iron Cross was the first to show up this year, but not til mid July. We had an exceptionally harsh winter, I had given up on it. Another variety with bright pink flowers showed up just a couple of weeks ago. The purple leaf variety showed up just a couple of days ago. All are much diminished from last year. I think I'm going to pot the last 2 varieties up for the winter, they were so late to show up, & we usually get our first frost mid October. We're having cooler weather earlier than normal though, so who knows.

So it sounds like they're barely hardy in your zone and/or you have them planted deeply? (just a guess)
Typically oxalis grows barely below the surface (or even 1/2 on top)...but in that sort of exposure, Iron Cross would certainly die (I think). I'm thinking some parts of yours were below the freeze damage line, and sprouted (finally) above the soil.

On a whim, I am trying these. Not only are hardiness zones all over the place but so are bloom times, planting depths and even prices.

I saw one site selling them 100 for $5 while others seem to want 10 for $5. Go figure...

Some places say that they bloom March - May, others say June to Sept.

One site claims Full sun only, others say Part Sun/Part shade.

I will plant some now before winter, others after just in case....

I think some of the confusion in the bloom times would be because in southern areas, they bloom in the winter and then if we get a heavy frost they hibernate for awhile, but are back up and blooming early in February and march -to may when they then get rust and disappear before the heat hits and stay gone till late september/october. Mine are up now. They like our cool weather and hate our heat and humidity. I have grown the purple leafed varieties and the wood sorrel grows itself.

Just thought I would add, these were originally planted quite shallow, I suppose it is quite possible over the years some might have moved deeper. We had an especially harsh winter last year. Most years we have a few days of temps under 10 degrees, last year we had several weeks of temps closer to 0, several days -15 or so. I was quite surprised that I had any survive. I had 4 varieties of oxalis, only 1, the newest, did not survive.

I grow these in pots, bringing them in in winter. They go into my south facing sun porch, away from the windows. I gradually let them go dormant.
Outside I have one pot in shade and one in the sun. The one in sun blooms, In fact it just finished. The one in shade didn't bloom at all.
I start watering them in March, and don't bring them outside until all danger of frost is over.

I received some as a "bonus" with other misc bulbs I ordered - forget the complany..... I was pleasantly surprised when I saw that they had sprouted this week. The flower is a such a pretty deep rose color. Mine are planted along a northern edge of the garden under a Kronprincessan Victoria rose and next to a lenten rose. If they stay well behaved, I might use them more to tuck here and there along my edges.

I also have two pots of these bulbs, and give them about the same treatment as flowergirl. I think they are pretty nice. They bloom for me with just morning sun. Last year I repotted them into some new soil in the spring and threw the old soil out into the mostly shady flowerbed. They bloomed okay there with sun from 11 to one PM, but later than when the photo was taken. You can just see the buds starting.

I got a surprise one summer about 20 years ago when one came up in my vegetable garden. I like the plant a lot, but it has spread because I have tilled a bit. In pots it does not survive out side here in zone 8. I should move the dirt from the vegetable garden some where more suitable. I can imagine that mulching in the fall could allow them to survive eastern WA winters. I think that they could make a nice house plant also.