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Calibrachoa is a tender perennial grown as summer bedding, so its year has four clear phases. Spring is propagation and planting. Early summer is establishment, pinching and the start of the feeding routine. High summer is watering, feeding and one hard cutback. Autumn is taking cuttings and deciding what to overwinter before the first frost ends the display.
Almost everything that goes wrong is a matter of timing rather than technique: feeding started too late, the cutback left until the plant had nothing left, or cuttings taken after the parent had already been frosted. Working to the sequence below removes most of it.
| Season | Main job | What to watch for |
|---|---|---|
| Late winter | Increase water on overwintered stock; start weak feed | New shoots breaking from the crown |
| Early spring | Take cuttings from overwintered plants; pot on | Soft pale growth from too little light |
| Mid spring | Pinch young plants; harden off gradually | Nights still below 50F (10C); do not rush outside |
| Late spring | Plant up baskets after the last frost | Water in twice on planting day |
| Early summer | Pinch tips once; even watering; begin feeding at week six | Compost drying out on hot windy days |
| Midsummer | Weekly high-potassium feed; cut back by a third | Yellow leaves between green veins: iron lockout |
| Late summer | Continue feeding; take cuttings for next year | Aphids and thrips on new growth |
| Autumn | Bring stock plants in before the first frost | Flowers shrinking as nights cool; this is normal |
| Winter | Keep stock frost free at 45F to 55F (7C to 13C) | Whitefly indoors; water only just enough |
Spring: propagate, pinch and plant
As light returns in late winter, overwintered stock plants start pushing new shoots. Increase watering, begin a quarter-strength feed, and let the shoots extend until they are long enough to cut. Those shoots make the best cuttings of the whole year because they are soft, disease free and full of energy.
Take cuttings in early spring and root them at 65F to 72F (18C to 22C). Pot the rooted cuttings on into 3 inch (8 cm) pots and pinch the tips once they reach about 4 inches (10 cm), which is the single most effective thing you can do for a full basket later.
Plant up baskets only once all frost risk has passed and nights are reliably above 50F (10C). Harden off over a week first. Planting a fortnight early into cold compost gains you nothing; the plants sit still, and one cold night can cost you the whole batch.
Summer: feed, water and cut back once
For the first six weeks after planting the compost still holds its starter fertilizer, so the job is even watering and full sun. Pinch the tips once at about two weeks to force branching. From week six the plant is living entirely on what you give it, so a weekly full-strength high-potassium feed becomes the fixed routine, with an ericaceous or chelated iron feed substituted every third or fourth time in hard water areas.
Water by weight, not by the look of the surface, and never let a basket dry out completely; the band of dropped leaves partway along every trailing stem is the permanent record of one missed watering in a heatwave. In high summer that means daily, and twice daily in hot dry wind.
Somewhere around midsummer, when the center of the basket has gone bare and flowering is thinning, cut everything back by a third and feed immediately. The plant refills in about three weeks and then flowers hard until the frosts. Doing this once, on time, is worth more than any amount of extra fertilizer applied to an exhausted plant.
- Week two after planting Pinch the top inch out of every shoot. This is the cheapest way to double the number of trailing stems and it delays flowering by only a few days.
- Week six after planting Start the weekly feed and do not stop until the plant is finished in autumn. Mark this date; in your own compost the plants may run out sooner or later than six weeks.
- First sign of pale new leaves Switch straight to an iron or ericaceous feed rather than increasing the general fertilizer. Yellow between green veins on the newest growth means locked-up iron, not hunger.
- Midsummer Cut every stem back by a third to a half, feed the same day, and keep it evenly watered while it regrows. Avoid doing this in the middle of a heatwave.
Autumn and winter: cuttings and stock plants
Flowering continues right up to the first frost, which finishes the plant overnight, so the work of autumn has to be done before that happens rather than after. Take cuttings in late summer or early autumn while the growth is still soft and the weather still warm enough to root them in two to three weeks.
Choose which plants to keep as stock, cut them back to about a third and bring them under cover before the first frost. Keep them bright, frost free and cool at 45F to 55F (7C to 13C), water only just enough that the compost never dries right out, and stop feeding until late winter. Check the leaf undersides for whitefly and aphids before and after bringing them in.
Everything you are not keeping can be composted once frosted. Empty the baskets, wash them, and do not reuse the old compost for next year's calibrachoa; a season of hard tap water leaves it alkaline and exhausted, which is precisely the condition that causes the yellowing.
The notes that make next year easier
Keep a short record of six dates: when you took cuttings, when they rooted, when you planted the baskets, when you started feeding, when the leaves first went pale, and when you cut back. Add where each basket hung and how many plants went into it.
Two seasons of those notes replace all general advice with something specific to your own site and your own water. You will know whether your compost runs out at five weeks or seven, whether the south-facing bracket genuinely needs watering twice a day, how many weeks your baskets take to refill after a cutback, and exactly which week your water chemistry starts to bite so you can begin the iron feed before the yellowing appears rather than after.