How to Propagate Calibrachoa from Cuttings and Overwinter Stock

Why cuttings and not seed

Calibrachoa is propagated vegetatively. The plants grown for baskets set very little viable seed, and what seed does form does not come true, so there is no practical way to raise a basket from a saved seed head. This is also why the plant is self-cleaning and needs no deadheading: with almost no seed being set, spent flowers simply dry and drop rather than pulling energy into pods.

Cuttings, on the other hand, are extremely easy. The plant roots readily from soft shoot tips throughout the growing season, and a single healthy basket will supply thirty or forty cuttings without looking any thinner for it. Taking cuttings in late summer is also the cheapest way to carry the plant through winter, since young rooted cuttings overwinter in far less space than a whole basket.

Taking softwood tip cuttings

Take cuttings from soft, actively growing shoot tips. Avoid stems that are carrying flowers if you can, and if you cannot, pinch the flowers and buds off, because a cutting trying to flower puts nothing into roots. Work in the morning when the plant is fully turgid and keep the material out of the sun and in a bag until you get to the potting bench.

The best times are early summer, when the plant is growing fast and you want extra plants for a second basket, and late summer to early autumn, when you are taking cuttings specifically to overwinter. Cuttings taken in the cooling days of autumn root more slowly but still succeed if you give them warmth.

1. Cut a shoot tip Take the top two to three inches (5 to 8 cm) of a non-flowering shoot, cutting with clean scissors or a blade. Aim for a piece with three or four pairs of leaves on it. Take more than you need; they cost nothing and not all will take.
2. Trim below a leaf joint Recut the base cleanly just below a leaf joint and strip the leaves from the lower half of the stem, leaving two or three pairs at the top. Pinch off any flower buds. Large leaves can be halved to cut water loss.
3. Insert into gritty potting mix Use a fifty-fifty mix of all-purpose potting mix and perlite, moist but not wet. Push the cuttings in around the edge of a small pot so the lowest remaining leaves sit just above the surface. Rooting hormone is optional; calibrachoa roots well without it.
4. Keep humid and warm Cover with a clear bag held off the leaves, or use a propagator lid, and keep at 65F to 72F (18C to 22C) in bright indirect light. Never in direct sun, which cooks them within an hour. Ventilate daily to stop gray mold and remove any cutting that goes soft.
5. Pot up when rooted Roots appear in two to three weeks in warm weather, and a gentle tug that meets resistance tells you they are there. Remove the cover over a few days, then pot each one into a 3 inch (8 cm) pot of free-draining compost and grow on in good light.

Overwintering stock plants

Calibrachoa is a tender perennial rather than a true annual, so a plant kept above freezing will carry through the winter and grow away again in spring. Whether it is worth doing depends on space, but keeping two or three small plants rather than a whole basket makes it easy.

Bring plants in before the first frost. Cut them back hard, to about a third of their size, and stand them in the brightest, coolest frost-free place you have, ideally around 45F to 55F (7C to 13C). A cool windowsill or a frost-free greenhouse both work. Water very sparingly through winter, just enough that the compost never dries out completely, and stop feeding entirely.

The plant will look sparse and unimpressive until late winter. As light returns it starts to push new shoots, and those shoots are the ideal material for a big batch of spring cuttings. Increase watering as growth resumes, start a weak feed, and pot up into fresh compost before the plant goes back outside once the frosts have finished.

Overwintered plants are the commonest place for whitefly and aphids to survive indoors and reappear in spring. Inspect the undersides of the leaves before you bring anything in, cut off infested growth, and check the plants again every few weeks over winter.

Growing rooted cuttings on for spring

Young plants raised in autumn need to be kept just ticking over rather than pushed. Give them the brightest position you can, keep them frost free, water sparingly and do not feed until late winter. Overfed, underlit winter growth is soft, pale and floppy and never makes a good basket plant.

Pinch the growing tip out once the plant reaches about 4 inches (10 cm) tall, and again on the resulting side shoots if they run away. Each pinch doubles the number of shoots and is what separates a dense basket from three long straggling stems. Stop pinching about four weeks before you intend to plant out so the plants have flower buds by the time they go into the basket.

Harden off over a week or so before planting, moving the plants outside for progressively longer each day once nights are above 50F (10C). Then plant up as you would with bought plants.

Keeping records of your own stock

Label every batch with the date you took the cuttings and which plant they came from, and keep the label with them through potting up. Color is invisible on an unrooted cutting and easy to muddle, and a mixed tray with no labels means a basket that fights with itself once it is in full flower.

Record how many cuttings you took, how many rooted, and how long they took. After a season you will know your own strike rate and can take exactly the number you need. Note which parent plants performed best through the summer, because the point of propagating your own is that you keep the ones that actually did well in your conditions rather than starting again from scratch each spring.