Oxalis Dying Back After Flowering: Dormancy, Not a Dead Plant

The collapse is the most misread event in growing this plant

After a long run of leaf and a period of flowering, an oxalis stops. The leaves yellow from the oldest outward, the stalks lose their stiffness and lie across the rim, and inside two or three weeks there is nothing above the compost but a few limp stems. There is no obvious cause. Nothing was moved, nothing was over or underwatered, and the plant looked excellent a month earlier. It is easy to conclude you have killed it, and an enormous number of these plants go into the bin at precisely this moment.

What is actually happening is that the plant has finished a growth cycle and is retreating to its bulbs. Oxalis is a geophyte: the visible plant is a seasonal structure that gets built, used, and dismantled, and the permanent plant is the cluster of small scaly bulbs an inch (2.5 cm) below the surface. Through the collapse it is pulling everything reusable out of the dying leaves and packing it into those bulbs, which is why the leaves yellow rather than simply going brown and dry. Interrupting that process by cutting the foliage off green robs the bulbs of the reserve they are storing.

The trigger varies. Heat above about 80F (27C) sustained for a couple of weeks will do it. So will a long dry spell, shortening day length, or simply the plant having run the number of months its species runs. Some plants do it once a year with clockwork regularity, others do it twice, and a few grown in even indoor conditions never fully collapse and just thin out for a while. All of these are normal.

Telling dormancy apart from rot, which looks similar for a week

The one situation where a collapse is a genuine problem is bulb rot, and it is worth being able to tell them apart because the treatment is opposite: dormancy wants less water, rot wants the pot tipped out immediately. The distinction is usually clear within a minute of looking at the plant properly.

Dormancy is gradual and orderly. Leaves turn yellow before they go limp, the oldest first, over a couple of weeks, and the stalks stay dry as they collapse. Rot is fast and wet. Leaves go from healthy to gray-green and floppy in days without yellowing much, the stalk bases are soft and darkened and pull away from the compost with a wet snap, and there is often a sour smell in the pot. If you are in any doubt at all, tip the plant out of the pot and look. A dormant bulb is firm and dryish; a rotted one is brown, soft, and squashes between finger and thumb.

Tipping a pot out costs the plant nothing at this stage, so do it whenever you are unsure. If the bulbs are firm, put them back and go on with the rest. If some are soft, discard those, let the rest dry off on a sheet of paper for a day, and repot the survivors into fresh gritty potting mix.

Putting a pot to rest, step by step

The resting period is a straightforward job that takes about five minutes spread over a month. The one thing to get right is dryness. A dormant bulb has no leaves and therefore no way to use water, so compost that stays damp around it for weeks is the ideal condition for the rot described above.

1. Stop feeding as soon as the yellowing starts Fertilizer salts left in the compost of a pot that is no longer drinking will build up around the bulbs. The last feed of a cycle should be the one before you see the first yellow leaves.
2. Taper the watering over two to three weeks Halve the amount you give at each watering and lengthen the gaps, then stop entirely once most of the foliage has gone over. Do not cut water off abruptly while there are still green leaves working, because those leaves are still loading the bulbs.
3. Let the foliage die back completely before removing it Wait until stalks are yellow or brown and pull away with a light tug. Then clear the lot off the surface so that decaying leaf litter is not sitting on the compost. Never cut green foliage off to tidy a pot that is only part way through this.
4. Move the pot somewhere cool, dim and dry A shed, a garage, the floor of a cool cupboard or under a greenhouse bench all work. Aim for 50 to 60F (10 to 16C) and no water at all. Light is irrelevant to a leafless pot, so a dark spot is fine and often more convenient.
5. Leave it for four to eight weeks Four weeks is the practical minimum for most ornamental kinds and six to eight gives a stronger restart. Label the pot with the date you stopped watering so you are not guessing later. Check it once a month for shoots, which sometimes appear on their own.
6. Refresh the compost before restarting, every second cycle Tip the pot out, separate the bulbs, discard anything soft, and replant the firm ones an inch (2.5 cm) deep in fresh gritty mix. You will usually find several times as many bulbs as you planted, which is the moment to divide or to thin back to a sensible density.

Waking it up again

Restarting is a single decision: give it one thorough watering, put it in warmth and good light, and then leave it alone. Move the pot to a bright spot at 60 to 70F (15 to 21C), water until it runs out of the base, let it drain, and do not water again until shoots break the surface. That is usually two to four weeks. Watering repeatedly into a leafless pot in the hope of hurrying it up is the most common way to lose bulbs that survived the whole rest period intact.

Shoots come through as tight pink or pale spears that unroll into folded leaves over a few days. From that point growth is fast, and the pot fills out over six to eight weeks. Begin normal watering as soon as the first leaves are open, and hold the feed back until the pot is properly in leaf.

If nothing has appeared after six weeks of warmth and moisture, tip it out and look. Firm bulbs mean the rest simply is not over, so give it another month dry and try again. Soft bulbs mean it rotted, and the cause was almost certainly water during the dormant period.

A rested plant should come back thicker than it went away, because the bulb cluster has multiplied. If your restart is consistently thinner than the previous cycle, the usual reason is that the previous season's foliage was cut off or lost too early, so the bulbs never finished loading.

Plants that never quite go dormant, and what to do with them

Grown indoors at a steady temperature with consistent light, some oxalis simply keeps going. It thins out, flowers less, produces smaller leaves for a couple of months, and then picks up again without ever going bare. There is nothing wrong with this and no need to force a rest on a plant that is not asking for one.

It is worth forcing one deliberately, though, when the plant is clearly running down: fewer and smaller leaves cycle after cycle, stalks that flop, and flowering that has stopped. Withhold water until the foliage goes over, clear it, rest the pot dry and cool for six weeks, refresh the compost, and restart. This is the standard reset for a tired oxalis and it works far more reliably than feeding one.

The other reason to force a rest is convenience. A pot put deliberately to sleep needs no attention at all, which makes oxalis an unusually easy plant to own if you travel, or to move outdoors and indoors with the seasons. There is no penalty for choosing when the rest happens as long as you let the foliage die back properly first rather than cutting it off green.

Write the date you stopped watering directly on the pot label, along with the date you intend to restart it. A leafless pot of bare compost in a shed is the single easiest thing in a garden to forget about for a year, and bulbs left dry for many months come back weak.