Gadenin日本語Get the appYellow leaves in a basket are almost always locked-up iron
This is the single most useful thing to know about the plant. A calibrachoa basket that starts the summer deep green and turns a pale, washed-out yellow by midsummer is very rarely short of fertilizer. It is short of iron it cannot reach. Calibrachoa evolved on acid soils and takes up iron efficiently only when the compost sits around pH 5.5 to 6.2. Every watering with hard tap water adds calcium and bicarbonate, the compost drifts upwards through pH 6.5 and past 7, and at that point the iron already sitting in the pot becomes chemically unavailable. The plant starves in the middle of plenty.
The pattern is diagnostic if you look at which leaves went yellow. Iron shortage shows on the newest growth at the ends of the trailing stems first, and it shows between the veins: the leaf goes yellow or almost cream while the veins themselves stay a thin green net. The oldest leaves back near the crown stay green far longer. Nitrogen hunger does the exact opposite, starting on the oldest leaves at the base and turning the whole leaf a uniform pale green with no vein pattern at all.
The fix is an acidifying or iron-containing feed, not more general fertilizer. Use a liquid feed sold for ericaceous or acid-loving plants, or add a chelated iron tonic to the watering can. Chelated iron in the EDDHA or DTPA form stays available at higher pH than plain iron sulfate does, which matters if your water is genuinely hard. Applied to the compost, the plant regreens from the tips down over ten to fourteen days. Pouring on more balanced fertilizer at this stage makes the yellowing worse, because you are asking the plant to push out growth it has no iron to color.
| What you see | Where it starts | Cause | What to do |
|---|---|---|---|
| Yellow between green veins | Newest tips of trailing stems | Iron locked up by alkaline compost | Chelated iron or ericaceous feed; regreens in 10 to 14 days |
| Even pale green, no vein pattern | Oldest leaves near the crown | Genuine nitrogen hunger | Resume weekly balanced liquid feed |
| Yellow leaves that drop when touched | Lower half of the plant | Compost stayed sodden | Check drainage; let the top inch dry before rewatering |
| Whole stem limp and crisp | One or two stems only | That stem dried out completely | Cut it back to the crown; the rest recovers |
| Green plant, no flowers | Whole plant | Too little sun, or nitrogen-heavy feed | Move into full sun; switch to a high-potassium feed |
Rainwater is naturally slightly acidic and free of the bicarbonate that causes the problem. If you can collect even one butt of it, using rainwater on your calibrachoa baskets and tap water on everything else prevents the yellowing rather than curing it.
The basket must never dry out completely
Calibrachoa carries a very large amount of leaf and flower on a small root ball, and it does not tolerate drought the way a petunia does. A petunia that wilts in the afternoon will usually come back by evening none the worse. A calibrachoa that goes fully dry loses the fine root hairs, drops a band of leaves along every trailing stem, and takes three weeks to look right again even after you rewet it. That bare patch part way down each stem is the fingerprint of one missed watering in a heatwave.
Judge water by lifting the basket, not by looking at the surface, which dries within an hour of watering and tells you nothing. A watered basket is unmistakably heavy; a dry one swings easily on its bracket. In high summer a full basket in sun needs water once a day, and twice in hot dry wind.
Water until it runs freely from the base every single time. A half watering wets the top two inches (5 cm) and leaves the bottom of the root ball permanently dry. If a basket has gone bone dry and water now runs straight down the gap between the shrunken compost and the pot wall, stand the whole basket in a bucket of water for twenty minutes until the bubbles stop.
The one thing calibrachoa will not survive is standing water. Roots sitting in a saucer that never empties rot at the collar within days in warm weather. The symptom is a stem going limp and staying limp after you water, which is the opposite of the recovery you get from drought.
Feed weekly and never stop
The compost in a hanging basket is exhausted about six weeks after planting. From then on the plant lives entirely on what you give it, and calibrachoa is one of the hungriest things you can put in a basket. Feed a liquid fertilizer at full strength once a week, or at a quarter strength with every watering, which is gentler and gives a more even result. Do not stop feeding when the plant looks good; it looks good because you are feeding it.
Once the plant has filled the basket, use a feed higher in potassium than nitrogen, on the pattern of a tomato feed. High nitrogen carried through summer gives long soft trailing stems with wide gaps between the leaves and noticeably fewer flowers. Combine the two feeds through the season rather than choosing between them: a high-potassium feed most weeks, with an iron or ericaceous feed substituted every third or fourth week, keeps both the flower count and the leaf color where they should be in hard water areas.
- Weeks one to six after planting Water freely, and feed only lightly if at all. The compost still holds its starter fertilizer. Let the plant fill the basket and start trailing over the rim before you begin a feeding routine.
- From week six to the end of summer Full-strength high-potassium liquid feed once a week, or quarter strength at every watering. Never let the basket go a fortnight without feed once this point is reached; the pale, thin look that follows takes a month to reverse.
- Every third or fourth feed Swap in an ericaceous or chelated iron feed instead of the usual one. In hard water areas do this from the start of the season rather than waiting for yellowing to appear.
- Midsummer, if the middle goes bare Cut the whole plant back by about a third, feed immediately, and keep it evenly watered. New shoots break from the crown within a week and the basket is full again in two to three weeks.
You do not need to deadhead
Calibrachoa is self-cleaning. The spent flowers dry and drop on their own, and the plant sets so little viable seed that there is no seed pod pulling energy away from new buds. Nothing is gained by picking off individual dead flowers, and on a basket carrying several hundred blooms at once the job would be endless anyway. This is one of the real practical differences between million bells and the older large-flowered petunias, which do need deadheading.
What does help is a mid-season cutback. By high summer the center of the basket often goes bare while the trailing ends carry all the flowers. Shorten every stem by about a third with scissors, feed, and water. It looks brutal for a week and the basket is denser and more even than before within three weeks.
Sticky stems and leaves are also normal, not a sign of pests. Calibrachoa foliage is naturally glandular and slightly tacky. Judge insect problems by what you can see on the shoot tips and leaf undersides, not by stickiness.
What to record so next year is easier
Three notes make the following season noticeably better. Write down the week you planted the basket and the week you started feeding, because six weeks apart is a rule of thumb and your own compost may run out sooner. Write down the week the leaves first went pale, which tells you when your water chemistry starts to bite and lets you begin the iron feed a fortnight earlier next time.
Also record the position of each basket and the date of your midsummer cutback. A basket on a south wall and one on an east wall behave completely differently in the same summer, and knowing how long a cutback takes to refill lets you time the plant to be at its best for whenever you most want it.