Gadenin日本語Get the appTreat it as half succulent
The plant sold everywhere as a bedding geranium is botanically a Pelargonium, and that matters for one practical reason: it stores water in its thick jointed stems. It is not a thirsty leafy annual and it does not want the steady moisture you would give a fuchsia or a busy lizzie. A geranium that has gone soft and limp on a hot afternoon will be upright again by morning without any harm done.
That storage is also why the plant tolerates neglect far better than attention. A pot left dry for a week in mild weather loses nothing. A pot kept damp for a week loses roots, and roots lost in summer are not replaced quickly.
The working rule for the whole season is simple. Water hard, then wait until the compost is dry an inch (2.5 cm) down and the pot is noticeably light before you water again. In high summer in a small pot that may be daily. In a cool wet spell it may be once a fortnight. The interval is set by the weather, never by the day of the week.
Yellow lower leaves mean too much water
Every grower meets this. The oldest leaves at the base of the plant turn a flat even yellow, sometimes with a brown papery edge, and drop off when you touch them. Nine times out of ten the compost is wet, the pot has no drainage or is sitting in a saucer of water, and the roots have been suffocating for a fortnight.
The plant is not short of nitrogen and it does not need feeding. Feeding a waterlogged geranium makes it worse. Stop watering completely, tip out any standing water, move the pot somewhere with more air and light, and pull the yellow leaves off so you can see whether new ones follow. If the compost is still damp four or five days later, the plant is in too big a pot or the compost is too heavy, and it needs repotting into something gritty and free draining.
Learn to tell that flat yellowing apart from the other things geraniums do. Yellow between the veins with the veins staying green on new growth is a nutrient problem, usually in old exhausted compost. Yellow rings or brown spots with a yellow halo on scattered leaves is a leaf disease, not watering. A single yellow leaf here and there through the season is simply the plant shedding its oldest foliage and needs nothing at all.
| What you see | Most likely cause | What to do |
|---|---|---|
| Even yellowing of the lowest leaves, compost damp | Overwatering, poor drainage | Stop watering, improve drainage, remove the leaves |
| Whole plant limp but compost bone dry | Simple drought | Soak thoroughly once; it recovers overnight |
| Pale yellow between green veins on new leaves | Exhausted compost | Half strength liquid feed every three weeks |
| Reddish or purple leaf edges in cool weather | Cold, not disease | Move somewhere warmer; color fades as it warms |
| Stem black and soft at compost level | Stem rot from wet compost | Take cuttings from the top now; the base is lost |
Write down the date you last watered each pot for the first month of the season. Most people are astonished at how short the real interval is, and that one record breaks the habit of watering on a schedule.
Feed sparingly and low in nitrogen
A geranium in fresh compost needs no feed for the first six to eight weeks. After that, a liquid feed at half the strength on the bottle every two or three weeks is plenty. Choose something higher in potassium than nitrogen, of the kind sold for tomatoes, because nitrogen goes straight into leaf.
An overfed geranium is unmistakable and disappointing. The leaves get large, dark and soft, the stems get thick and space out, and the flowering stops almost entirely. Nothing is wrong with the plant and nothing needs treating. Stop feeding, let it dry harder between waterings, and buds appear again in about three weeks.
Plants in the open ground in reasonable soil want no feed at all for the whole season. The commonest cause of a leafy flowerless geranium is a well manured bed.
Keep the plant open and tidy
Geranium leaves shed steadily all season, and a wet mat of yellow leaves and fallen petals lying on the compost is where botrytis starts. Clear it every time you water. Pull dead leaves off with a sideways tug at the base of the stalk rather than tearing them, so you are not left with a stub.
Pinch the growing tip out of a young plant once, when it has five or six leaves, to make it branch. After that the plant shapes itself and needs nothing beyond the removal of spent flower stalks. Do not shear a geranium over like a hedge in midseason; it responds by sulking for a month.
If a plant has gone bare and woody at the base by late summer, cut a third off the longest stems, cutting just above a leaf joint. It breaks from those joints within a fortnight and gives one more flush of flower before the season ends.
- Check by weight, not by eye Lift the pot. A dry pot is startlingly light and a wet one is heavy. The compost surface dries within hours in sun and tells you almost nothing about what is happening at the roots.
- Water until it runs out of the base Half watering wets only the top layer and drives roots upward. Soak the pot thoroughly, let it drain fully, and then leave it alone until it is light again.
- Empty the saucer every time A pot standing in water for a day is the single most reliable way to produce yellow lower leaves and stem rot. If a saucer is unavoidable, put the pot on pebbles above the water line.