I've never tried to grow an oxalis. I usually have it outside in a moist shady spot. maybe cooler temps and lots of water is the key?

Oxalis will appreciate a soil that you can keep moist but will still have plenty of aeration. I tend this plant for my mom in a south window behind shears & use Foliage-Pro 9-3-6 on it because it contains ALL the essential nutrients, but you would do well with any other 3:1:2 ratio fertilizer (like MG 12-4-8 or 24-8-16, both 3:1:2 ratios as well).

No matter what you do, the plants will at times look ratty. They may be telling you they need a rest. I've had good luck withholding water at that time for several weeks and letting the plants die back before starting my water/fertilizer regimen again.

Burned leaf margins could be a sign that soluble salts levels in the soil are too high, or you're using too much fertilizer. Fertilize every couple of weeks with a 1/4 strength dose ONLY when the plants are growing well, unless you're using a soil that allows you to water profusely at every watering (so at least 10-15% of the total volume of water used exits the drain hole), in which case you can fertilize more frequently at low doses with no concern for salt build-up.

Al

Hmmm, maybe it is an issue of water, then. I am a chronic underwaterer. I also thought that since they have bulbs/tubers (not sure what it is, exactly) that too much water could rot them... but perhaps that is just because I know that other plants with such structures are prone to rot. I guess that can't be true for everything, though, otherwise bog or aquatic plants with bulbs wouldn't be able to survive... good to be reminded of that.

Do they prefer a fertilizer that is higher in nitrogen? I've been using a fairly balanced fertilizer (I think it is 14-12-14). No burned leaf margins, and I water until it drains out the holes. Sometimes I water straight from the tap instead, so I'm not fertilizing every single time either. Mainly, it is the frequency of times that I water that is an issue. Luckily, it is near the kitchen sink, so it is less a victim of my underwatering than some.

I'll try more frequent watering then. I'm still curious about the fertilizer ratios, though. The only fertilizer I have with higher nitrogen numbers is one designed for orchids grown in bark, and I think it's something like 30-15-15.

Thanks for the input!

Some plants like moist soils, but insist on excellent drainage (potatoes and blueberries come to mind). Oxalis likes a moist soil, but doesn't tolerate wet feet well. The key then, is a well-aerated, fast draining soil that you CAN water frequently without the worry of water retention so great there is a risk of rot.

If you could take an average of all the plants, you would find they use NPK in a ratio of about 3:.5:2. Fertilizers with a ratio of 3:1:2 (examples: 24-8-16, 12-4-8, 9-3-6) very closely match this ratio. If you look at the P and say why is there more P in the 3:1:2 ratio fertilizers than the plant uses, it's because P is not measured in how much P there actually IS in fertilizers. It's a measure of how much phosphorous oxide (P2O5) there is in the blend. To get the actual amount of P in the fertilizer, you would multiply by .43, so the 3:1:2 ratio fertilizers supply nutrients in almost exactly the same ratio as plants use. I'm already way more technical than I wanted to get, but I thought I'd explain about the ratios, since you asked. If you want to know WHY it's better to use a fertilizer with nutrients in a ratio closer to what plants use, just ask.

Al

Hi Quinnfyre. I have purple oxalis..do you think they have the same needs?
Mine started as one bulb, multiplied over the years. It's in a south window. As for fertilizer, it gets All Purpose once or twice a year.
It's best to water during the morn/early afternoon..they tend to sleep at night..notice the leaves fold around dark?
They bloom several times a year..when flower fade, they're then deadheaded.
That's it..
Hope all is well with you..haven't seen you around..Toni

I'm assuming they have the same needs. Funny you should mention the leaves folding. I never had one before, and it seemed like every time I looked at it, it was all folded up, and I sort of wondered what was up with it, but as it was an impulse buy, it wasn't going to bother me if it didn't last. Well, one day, I actually saw it in daylight for the first time in a while, and then I figured it out... it folds its leaves up at night. That amused me.

I use the fertilizer that I use because I have more African violets than anything else (it's a urea free fert balanced for AVs), and I mix up a large batch of fertilizer and water and store it in my room so I don't have to lug watering cans of water up two flights of stairs every time I need to water. Once the weather starts warming up, I'll probably start mixing up a bloom booster formula as well, for non-AV flowering plants (like jasmine) for the extra phosphorous. Is it detrimental to your average houseplant (such as oxalis, pothos, peperomias, dracaenas, etc) to be using the 14-12-14 formula? If so, I'll see what else I have that I can use, and mix up yet another set.

I've been good, Toni. I was actually going to say the same thing, haven't seen you around. Usually I am in the orchid forum though. You still doing well with your violets?

It's pretty much a certainty that high-P fertilizer formulas provide far more P than a plant can ever use. E.g., a popular blend like MG 15-30-15 provides 12 times more than a plant could ever use (compared to N). Here's something I wrote about it a while ago.

Lets first look at the role of fertilizers in general. There are 6 factors that affect plant growth and yield; they are: air, water, light, temperature, soil or media, and nutrients. Liebig's Law of Limiting Factors states the most deficient factor limits plant growth and increasing the supply of non-limiting factors will not increase plant growth. Only by increasing most deficient factor will the plant growth increase. There is also an optimum combination of the factors and increasing them, individually or in various combinations, can lead to toxicity for the plant.

From the above, we can say that when any nutritional element is deficient in the soil, plant growth slows. We have a term for this occurrence: environmental dormancy. When the deficient element is restored to adequacy levels the environmental constraint caused by the deficient element is eliminated and plant growth can resumes at a normal rate, as long as there are not additional limiting factors. Continuing to increase the element beyond the adequacy range offers no benefits and can deleteriously affect the plant - often in several ways, depending on the element.

Somewhere along the way, we curiously began to look at fertilizers as miraculous assemblages of growth drugs, and started interpreting the restorative (of normal growth) effect of fertilizer as stimulation beyond what a normal growth rate would be if all nutrients were adequately present in soils. ItÂs no small wonder that we come away with the idea that there are Âmiracle concoctions out there and often end up placing more hope than is reasonable in them. In couplet with the hope for the Âmiracle tonic is Âmore must be betterÂ. IÂll use the latter idea as the lead-in for my thoughts on high-phosphorous fertilizer blends.

Among container growers you often find common belief that high-phosphorus (P) content fertilizers are a requirement for promotion of root growth and/or flowering. Fertilizer blends like 15-30-15, and even 10-52-10 are sold under names that imply that you actually NEED these formulas for plants to bloom well and to produce strong roots. Lets examine that idea in a little more depth.

While anecdotal evidence abounds, there is very little scientific evidence to show any need for such products. IÂve mentioned in other posts that high-P fertilizers are a historical carry-over from when it was most common for plants to be started in outdoor soil beds, the soil in which was usually still quite cold at sowing time. Both the solubility of P and plants ability to take it up are reduced in cold soils, so it was reasoned that fertilizing with high levels of P insured that at least some would be available during periods of growth in chilled soils.

We know that tissue analysis of leaves, roots, flowers - any of the live tissues of healthy plants will reveal that P is present in tissues at an average of 1/6 that of nitrogen (N) and about 1/4 that of potassium (K). Many plants even contain as much calcium as P. If we know that we cannot expect P to be found in higher concentrations in the roots and blooms than we find in foliage, how can we justify the belief that massive doses of P are important to their formation?

It is well known among experienced growers that withholding N when all other nutrients are available at adequate levels induces bloom production, even on smaller and younger plants. Though plants USE nutrients at approximately a 3:.5:2 ratio (note that N is 6 times the level of P, and K is 4 times the level of P), most greenhouse operations purposely fertilize with something very near a 2:1:2 ratio to limit vegetative growth so they can sell a compact plant sporting pretty blooms to tempt you.

Simply limiting N limits vegetative growth, but it does nothing to limit photosynthesis. The plant keeps making food, but it cannot use it to grow leaves and extend stems because of the lack of N. To where should we imagine the energy goes? It goes into producing blooms and fruit.

What harm might there be in a little extra P in our soils? First consider that the popular 10-52-10 has almost 32 times more P than a huge percentage of plants could ever use. Even 1:1:1 fertilizer formulas like the popular 20-20-20 are already high P formulas because they have 6.25 times more P (in relation to N) than plants require to grow robustly and normally.

Evidence of phosphate over-fertilizing usually always includes some degree of leaf chlorosis. P competes with iron (Fe) and manganese (Mn) ions for attachment sites and causes antagonistic deficiencies of these micronutrients. Unfortunately, the deficiency of these elements causes interveinal chlorosis (yellowing), and the first thing we normally consider as a fix for yellow leaves is more fertilizer, so we give the plants a good dose of our favorite bloom-bomb which causes, no surprise - worsening of the condition.

IÂll close with an anecdote of how I used to fertilize plants with showy blooms before I had a better understanding of the overall picture. I would fertilize with a "bloom-boosting" fertilizer as long as foliage was bright green. As foliage inevitably yellowed, I would then switch to a high N formula until the color returned and start the cycle over again. I THOUGHT that the P was helping produce blooms and the yellowing was caused by a lack of N, which I quickly jumped to correct at the first evidence of yellow. I now understand that the high levels of P were what were causing the yellowing and it wasnÂt my returning to a high N formula that greened the plant up again, it was the reduction in the level of P in the soil when I stopped using the high-P formulation.

Al

Fascinating. I bought the bloom boosting formula because I was told that certain plants (dahlias and jasmine, in my case) required a high phosphorus concentration both in order to bloom, and to reduce "leggy" growth. I rarely used it however, because it was annoying to try and mix up a gallon's worth when all I needed to use it for were a few plants. The rest got some sort of Miracle Gro fert at the time. Now I've switched over to AV fertilizer (in this case, Optimara) and I've been using that pretty much exclusively.

It's food for thought. I'll have to decide how I want to deal with this. My focus is on African violets and mounted orchids, and the other houseplants are nice extras, although numerous enough for me to take this info into consideration.

Thanks! Happily, this went to my email, so I'll have a copy there that I won't have to do a search for : )