Gadenin日本語Get the appThe leaves folding shut at night is the plant working, not wilting
Almost everyone who grows oxalis for the first time has a moment of alarm in the evening. The mound of leaves that was open and flat all afternoon has collapsed into a cluster of closed umbrellas, each leaflet hanging straight down and folded along its midrib, and the whole pot looks as though it has been left dry for a week. By mid morning the following day it is flat and open again. This is a daily movement called nyctinasty, driven by water pressure in a hinge of cells at the base of each leaflet, and every healthy plant does it. Nothing is wrong.
It is worth knowing because it gives you a reading on the plant. Leaves that fold in the middle of a bright day are telling you something: usually that the light is too fierce and the plant is reducing the surface it presents to the sun, or that the compost has gone dry and it is cutting water loss. Leaves that stay half shut all day, morning included, mean the light is too dim to be worth opening for. Leaves that stop moving altogether, staying limp and open through the night, usually mean cold damage or rot at the base.
The flowers do the same thing, closing at dusk and on heavily overcast days and opening again when the light comes. A pot that seems to have stopped flowering during a dull spell has usually just shut its flowers, and they reopen on the next bright morning.
Light is what keeps the purple purple
The dark purple leaf color is anthocyanin pigment, and the plant makes it in response to light. Move a richly colored pot into a dim corner and within three or four weeks the new leaves come through a muddy bronze-green, the stalks stretch, and the tight mound turns into a sprawl of long-stemmed leaves that flop over the rim. That is the single most common complaint about this plant, and it is entirely a light problem. Feeding it does not help and usually makes the stretching worse.
Aim for a position that gets several hours of direct sun in the milder part of the day, plus bright indirect light for the rest. An east-facing window is close to ideal indoors. A south or west window works if there is a sheer curtain or a couple of feet of setback, because unfiltered midday sun through glass in high summer will scorch the leaf edges to a papery brown within a day or two. Outdoors in the growing season it takes considerably more sun than it does indoors, because there is air movement and no glass concentrating the heat: morning sun with afternoon shade suits it well.
Turn the pot a quarter turn every time you water. Oxalis leans toward light hard, and a pot that is never turned develops a bare back and a leaning front within a month. The green-leaved forms are slightly more tolerant of moderate light than the purple ones, but they all stretch eventually. Under electric light, twelve to fourteen hours a day at eight to twelve inches (20 to 30 cm) from a decent LED unit keeps both the color and the compact habit.
Watering: the top inch, and the two moments to stop
In full growth, water when the top inch (2.5 cm) of compost is dry to a pushed finger, and water thoroughly enough that it runs out of the base. In a warm bright room a six inch (15 cm) pot in full leaf will want that every four to seven days; outdoors in summer heat it can be every other day. Empty the saucer within half an hour. Oxalis has small bulbs sitting shallowly in the compost and they rot readily in a pot that stays saturated.
There are two moments to stop watering, and getting them right is most of the skill of growing this plant. The first is at planting or restart, before there are leaves, when the pot should stay barely moist at most until shoots appear. The second is when the plant begins to fade at the end of its growth cycle, with leaves yellowing and stems collapsing across the rim. That is dormancy starting, and the correct response is to reduce watering and then stop entirely, not to water more.
Tap water is fine. Oxalis is not fussy about water quality and shows no particular sensitivity to hard water or to chlorine. Water at the compost surface rather than over the leaves where you can, mostly because water sitting in the crowded leaf mound in cool conditions encourages the fungal leaf problems this plant is prone to. Do not mist it. Misting does nothing useful for a plant with this leaf structure and it keeps the foliage damp for hours.
Temperature, feeding, and reading trouble off the leaves
Oxalis grows best between 60 and 75F (15 to 24C). It slows above 80F (27C) and prolonged heat is one of the triggers that sends it into dormancy early, which is why plants in a hot conservatory often collapse in midsummer while a plant on a cooler windowsill keeps going. Most of the ornamental kinds are damaged below about 40F (5C) and killed by a real freeze at the bulb, so pots living outdoors in the warm months need bringing in before the first frost.
Feed only while the plant is actively growing: a balanced liquid feed at half the recommended strength, every three to four weeks. Stop as soon as the leaves start to yellow at the end of the cycle. High-nitrogen feed produces long soft stalks that flop, and a plant that has been overfed all season goes into dormancy with soft bulbs that rot more easily. Groom as you go by pulling out yellowed leaves and spent flower stalks with a gentle tug at the base; they come away cleanly and the pot looks better for it.
| Symptom | Likely cause | What to do |
|---|---|---|
| Purple leaves fading to dull bronze-green | Not enough light | Move to an east window or add several hours of direct sun |
| Long stalks flopping over the pot rim | Low light, or too much nitrogen feed | Increase light, halve feeding, cut the worst stalks out |
| Leaf edges papery and brown | Scorch from unfiltered midday sun through glass | Filter the light or set the pot back from the window |
| Leaves folded shut through a bright afternoon | Dry compost or excessive heat | Check the top inch and water; move out of direct heat |
| Whole plant yellowing and collapsing at once | Dormancy beginning, which is normal | Stop feeding, taper watering, let it die back |
| Base of the stalks brown and mushy | Rot from overwatering or a blocked drainage hole | Stop watering, tip out and inspect the bulbs |
| Fine pale speckling on the upper leaf surface | Spider mites, common in warm dry indoor air | Check the leaf undersides and treat immediately |
It will collapse, and that is not a failure of care
The single most important thing to know about caring for oxalis is that at some point the plant you have been looking after well will fall apart. The leaves yellow, the stalks go limp, and within two or three weeks the pot is bare compost. This happens after a flowering period, it is triggered by heat, day length or simply the plant having run its cycle, and it is not something you did wrong. The bulbs underneath are alive and are packing away reserves for the next flush.
Enormous numbers of these plants get thrown out at exactly this point, and it is a shame, because a rested pot comes back thicker than it was. The correct response is to stop watering, put the pot somewhere cool and dim for several weeks, and then start it again. That cycle is covered in full in the dormancy guide.
The practical consequence for care is simple: do not escalate. When a pot starts to fade, resist the instinct to feed it, repot it, move it to brighter light or water it harder. Every one of those interventions on a plant heading into dormancy makes rot more likely. Reduce, wait, restart.
The four things worth recording
Oxalis runs on cycles rather than on a calendar, and cycles are exactly the thing that memory handles badly. Four notes per pot per cycle turn a plant that seems unpredictable into one you can plan around.
Record the date the pot restarted, meaning the day you first watered it after a rest. Record the date the first leaf opened, which gives you the lead time between those two events in your conditions. Record the date the first flower opened. And record the date the leaves began to yellow in earnest, which is the start of the next dormancy. After two cycles you will know how long your plant runs in leaf, which is typically somewhere between five and nine months depending on the species and how warm you keep it.
Add a note of where the pot stood, because light position is the variable that changes the result most and the one people forget having changed. A short line such as east window, half strength feed monthly, first flower five weeks after first leaf, is enough to reproduce a good season deliberately instead of by luck.
If you grow more than one kind of oxalis, keep the records separately. The purple-leaved sorts and the four-lobed sorts run on noticeably different cycle lengths, and averaging them gives you a schedule that fits neither.