In my opinion Oxalis like night time temperatures 40 to 45 degrees and 60 plus in the day time. That's the overall objective.
When temperatures drop into the lower 20's, I use a thermal blanket and cover the top and doors of the frame. There's lots of condensation inside on the clear plastic of the frame. The blanket does get covered in snow and ice, but it tends to eventually melt as inside the frame is warmer than the surroundings. The Oxalis are nice and snug. Just don' t get your hands wet while watering at 20 degrees! Oxalis always need good air circulation. That's one of the problems with growing them indoors.
Very important to get this right. For South African plants I use 5 parts course sand, 2 parts small pebbles, 1 part professional potting soil and 1/2 part perlite. I get the sand and small pebbles at the neighborhood materials store as 50 pound bags each. The sand is sold as concrete sand and costs $2.95 and the pebbles are $3.95. A really small investment. I go through more than 200 pounds of sand a year. The mixture is created in a large pail. Remember to wash your perlite!
I also use one inch of wet potting soil at the bottom of the pot. This prevents the sand and bulbs from falling out the bottom. Most North and South American Oxalis use strictly professional potting soil mix.
Oxalis from the Pacific Northwest grow well in spagnum moss. South African bulbs will rot in soil too organic. Solid fertilizer is not required. Oxalis are able to get most of what they need in the Oxalis mix.
I also use only Terra cotta pots as they have great drainage. I use them with great results and have no experience nor opinion using any other types of pots. The best pot size should be 5-6 inches across.
My cold frame is situated over 20 stories high with direct southern exposure sunlight. I believe that many South African species need lots of sun. They can never get enough sun. The North American Wood Sorrels like more shade or filtered sun. Some of these love lots of sun too. Its really a judgment call per plant. You need to document these notes and attempt to make better plant placement the next season. I've learned you can't remember everything.
South African Oxalis need lots of water. Remember its they're rainy season. Heat builds up in the cold frame to 70 degrees or more on sunny days so the sand dries out quickly. A little water in every pot goes a long way which allows for better flowering and propagation. To sum this up do a soaking water, let it dry out over a day or so then water again. Other Oxalis get watered when dry, but they all tend to get a little water almost every day.
Oxalis that are not watered can go dormant early, which can mean plant failure if its original bulb needs to produce a new bulb to survive. Pacific Northwest species get watered like my Orchids.
There is no question that bulbs need to be planted at the first signs of growth. Sometimes this can not be possible because of space limitations or bad weather. Bulbs are significantly weakened if they are put through the stresses of no growth when they want to grow. Most bulbs will die if not planted in their next growing season.
Some Oxalis like the Flavas and Polyphyllas generally need to propagate new bulbs to carry on the species for the next year. If the plant is forced into early dormancy for any reason such as
temperature, wrong soil, drought or pests the plant will most likely die, because the current bulbs will have become soft, incapable of supporting life for the next growing season.
Plants that are allowed to freeze will probably die as well. You know it is over when the stem begins to rot and soften at the level of the sand. If you dig up the bulbs and they have become soft and no longer viable.
For years my biggest problem was Aphids. Aphids come in different types and will suck all the life out of your plants. They come as green ones, black ones, large and small. But when they infest a plant it usually means doom. The key to Aphids is a product sold in the USA called Azitin XL (Azadirachtin). They claim is non human nor phytotoxic. I read that in Africa its used for toothpaste, but I didn't rush to try it. A concentrated quart is expensive, maybe $150.00!, but it makes never ending gallons of solution for my spray bottle. It doesn't kill the Aphid, but it interferes with its reproduction cycle and prevents them from making more Aphids. It doesn't really hurt the South African Oxalis, though I question if there's a reduction in the flowering. It does however appear to burn the leaves of all North American Oxalis, but has yet to do that to any South Africans; curious. If sprayed on the bottom and tops of the leaves, twice a day, it controls the Aphids and they just eventually vanish.
There's also tea solution with soap mixture. This will kill the Aphids, but its not a long term solution to the problem. Also ladybugs don't work, because they leave.
Some plants are generally Aphid proof. Oxalis Crassipies and Articulata rarely ever have Aphids on them, while some South African plants are more suceptible to Aphids than others.
Spider mites are also a problem. They won't kill a collection like the Aphids will. The infected plant just needs to be removed and isolated. I've yet to find a spray that doesn't hurt the plant.
Mice. Well you know there's one around if you have a tunnel leading down the center of the plants soil. I have already lost several Oxalis in August 2001 to a mouse that found every bulb in a pot. I had a whole pot of Oxalis Rhomboidea and I was left with one bulb. I have now propagated four more bulbs and now have five planted for this year. Its a work in progress. Sticky traps will get them every time. A quick experienced eye will prevent problems with mice if handled swiftly.
Some of my friends get rust for which they use some kind of fungicide. I never get rust and therefore have no experiences to share.
There is one last issue and that's overcrowding your pot with bulbs. Though it may not lead to plant failure, what happens above the soil is related to how much room a given bulb has between the next bulb. For South African plants mature bulbs need space between other mature bulbs. I have found that it is more important to let a mature bulb grow then to put lots of bulbils around it. The Oxalis needs room to spread its roots and doesn't need bulbils to compete with. This effects flowering and future propagation. The bulbils should be either planted separately or given away for others to raise.
Your Oxalis usually only grows, during the course of a year, for several months of maybe a season or two. There's no question that bulbs mature best when the pot is removed of its dead leaves and left standing in a cool dry dark spot until its ready to grow again.
For me this is impossible as I need more room for my summer plants, When the South African Oxalis begin to wither in April-June the bulbs are removed and stored in non-air tight bags. I usually rinse the bulbs with water, then dry them out over two days. They are then packaged and labeled. Visually, I know exactly when it comes time for planting.
I plant a winter growing Oxalis as soon as I see growth from the bulb. The faster its planted in mid to late summer, the more time it has in growth with good temperatures. That's why I have some in full growth in September. The plant goes dormant in February or March which gives me room to plant something else.
There are lots of Oxalis that can not survive outside of soil. Oxalis Regnellii and Articulata all need full soil all year round. They can never be bagged and stored for months; if so you're creating plant failure. But most of the bulbous North American species need to sit in their respective bags for more than half a year. They withhold water completely and if stored and
handled correctly you can be assured that they will be ready for full growth.
Growing Oxalis can be considered an labor of love. Your plants do better with experience, but they can be complicated and difficult to grow. Each plant is a little collectors item.
Excess bulbs should be shared with others that have an interest. Just because I have set up an environment that works, doesn't mean that someone else can grow the same Oxalis with the same successes that I've had. My instructions are explicit and work for me in my planting zone which means they may not work for the reader, at another given place.
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