How to Plant Calibrachoa in Hanging Baskets and Containers

Choosing plants and when to put them out

Calibrachoa is bought as small plants, plugs or rooted cuttings; it is not raised from seed in the way petunias are. Look for compact plants with several shoots breaking from the base rather than one long trailing stem, and check the leaf color before you buy. A plant that is already pale yellow between the veins on its newest growth has been sitting in hard water and will need an iron feed from day one.

Plant into baskets when all danger of frost has passed and nights are reliably above 50F (10C). Calibrachoa is not frost hardy and cold nights below about 40F (4C) stall it badly even without a frost. If you plant up earlier under cover to get a head start, keep the basket in a frost-free greenhouse or porch and harden the plants off over a week before hanging them outside.

There is no advantage in planting into a large basket early and waiting. The plant only starts trailing once its roots have filled the container, so a young plant in a big volume of cold wet compost simply sits still and is more likely to rot than to grow.

Compost and container

Use a free-draining all-purpose potting mix with about a fifth by volume of perlite or coarse grit mixed through it. The plant needs a compost that holds moisture without ever staying sodden, and standard basket compost straight from the bag is usually a little too retentive on its own.

If your tap water is hard, start with an acidic potting mix or mix a third of it into ordinary compost. It gives you a lower starting pH, which delays the alkaline drift that causes midsummer yellowing by several weeks. It is much easier to keep the compost acidic from the start than to correct it once midsummer yellowing has already set in.

Container size matters more than people expect. A 12 inch (30 cm) basket is the sensible minimum, and a 14 to 16 inch (35 to 40 cm) one is far easier to keep alive because it holds enough compost to survive a hot day without going bone dry. Every basket must have free drainage, and any container standing on the ground must not sit in a saucer of water.

Adding a water-retaining gel to basket compost is worthwhile for this plant given how badly it takes drying out, but mix it at the rate on the packet and no more. Overdosed gel makes a permanently sodden core and rots the crown.

Planting up a basket

The aim is to get the plants evenly spaced near the rim, with the crowns just proud of the compost and the whole thing set low enough to hold a proper reservoir of water when you fill it.

Work in the shade and have the compost already moist before you start. Dry compost in a basket is very difficult to wet properly afterwards, and the first watering of a newly planted basket is the one that sets whether the root balls make contact.

1. Line and part fill Line the basket if it needs one and fill it about two thirds with your prepared compost mix. Firm it lightly. Leave enough room that the finished compost surface will sit about an inch (2.5 cm) below the rim.
2. Space the plants around the edge Set the plants evenly around the basket, an inch or two in from the rim, angled slightly outwards so they trail over rather than up. Four plants in a 14 inch (35 cm) basket sit roughly at the quarter points. Do not put one in the dead center of a small basket; the middle fills itself.
3. Set the crowns at the right depth Plant each one so the top of its root ball is level with the surrounding compost, never buried. A buried crown stays wet and rots. Fill between the plants, firm gently with your fingers and leave that inch of watering space at the rim.
4. Water in thoroughly Water until it runs freely from the base, then water again ten minutes later. The second pass is what wets the original root balls rather than just the compost around them. Check by lifting one edge of the basket to feel the weight.
5. Settle it in the shade for a few days Keep the basket out of full midday sun and hard wind for three or four days while the roots move out, watering every day or two. Then hang it in its final full-sun position.

Do not mix calibrachoa in the same basket with plants that want to dry out between waterings. It works well with other continuously thirsty summer bedding, but paired with something drought-tolerant one of the two will always be wrong.

The first six weeks

New compost carries enough starter fertilizer for roughly six weeks, so feeding is not urgent at first. What matters in this period is even watering and full sun. Water every day or two, never letting the basket dry right out, and check by weight rather than by looking at the surface.

Pinch out the growing tips once, about two weeks after planting, when the plants have taken hold and started to extend. Taking the top inch off each shoot forces branching from lower down and gives you a much denser basket than one long stem per plant. It costs you nothing in flowering time because the branches flower as soon as they grow.

Begin the weekly feeding routine at about six weeks, and in a hard water area include an ericaceous or iron feed in the rotation from the start rather than waiting for the leaves to go pale.

What to write down on planting day

Note the date you planted, the size of each basket, how many plants went in it, and where each one was hung. This one set of notes answers most of next year's questions: whether four plants were enough for that basket, whether the south wall position needed watering twice a day, and how many weeks passed before the compost ran out and the plants first looked hungry.

Also note whether you used acidic potting mix or ordinary compost in each basket. Comparing two baskets side by side over a single summer tells you more about whether your water is causing the yellowing than any amount of reading, and the answer is specific to your own tap.