Ornamental · Solanaceae
Calibrachoa
Calibrachoa × hybrida
Hand it full sun, steady water, and acidic soil, and calibrachoa pours small bell-shaped blooms over the rim from spring to frost.
Full sun
Every 1–3 days
USDA 9–11
3–12 in · 8–30 cm
Overview
Calibrachoa is the plant most gardeners meet as Million Bells: a low cascading flower hung with small, petunia-like blooms that tumble over the lip of a pot or basket all season. It sits in the nightshade family and stands close to the petunia, yet it earns its own name. The flowers come smaller, the stems run more mounding and trailing, and the color range pushes deeper than its cousin's.
It grows as a warm-season annual across most of the country, a tender perennial that only carries through winter in the mildest zones. The plant takes to heat and sun, drops its faded flowers without a hand on them, and keeps the bloom coming without a break. That steady output across a long summer is what packs it into so many containers.
In return it asks for a few things. It is a hungry, thirsty grower that wants slightly acidic soil and even moisture, and it sulks the moment it sits in shade. Line up the sun, the feeding, and the soil pH, and the plant largely runs itself.
Care
The short version: full sun, even moisture in a fast-draining pot, and a slightly acidic mix fed every couple of weeks. Pinch the trailing tips now and then to keep the plant dense, and leave the spent flowers to drop on their own.
Light
Calibrachoa wants full sun, 8 or more hours a day. The bloom thins quickly as shade builds, so a spot that bakes in afternoon light gives you the densest, deepest-colored plant.
Water
Hold the mix evenly moist but never soggy. Under summer heat the baskets and pots can run dry in a day, sometimes faster, with the surface drying within a day or two. Always plant into a pot with drainage holes, since standing wet at the roots is what brings on rot.
Soil
Set it in a well-draining, organically rich potting mix kept on the acid side, somewhere near pH 5.0 to 6.5. A peat-based mix suits it well. Steer clear of heavy clay in beds, which grips too much water for these roots.
Temperature
It rides a wide band, from about 41°F to 95°F (5°C to 35°C), and takes summer heat without complaint. Frost is the firm cutoff, which is why most gardeners run it as an annual.
Humidity
Average humidity of 40% to 60% keeps it content, so it is not a plant you watch the gauge for. Open air moving through a crowded basket does more for it than any number on a meter.
Feeding
This one is a heavy feeder. Work a slow-release balanced fertilizer into the mix at planting, then follow up with a dilute water-soluble balanced feed every other week. If the new leaves go yellow, add some chelated iron or iron sulfate to bring the green back.
Pruning
There is no deadheading on the list, since the faded flowers fall away by themselves. Pinch the stem tips back about 2 in (5 cm) at planting or midseason to hold the plant compact and push fresh branching and bloom.
Repotting
Calibrachoa is rarely repotted. It runs as a single-season container plant and gets swapped out each spring, so once it settles into its pot or basket it stays put for the year.
Size & spacing
The plant keeps low and spreading, around 3 to 12 inches (8 to 30 cm) tall with a trailing reach of 12 to 24 inches (30 to 60 cm). That mounded, cascading shape is exactly what lets the stems spill over the edge of a basket.
When to plant
Calibrachoa lives for warmth and will not stand frost. Set it out in spring once the cold has lifted and the soil has warmed past 55°F (13°C), and it flowers from late spring all the way through to the first frost that ends the run.
Northern hemisphere
Southern hemisphere
Typical months for a temperate climate: start earlier in warm zones, later where spring frosts linger.
- Plant: spring, after the last frost once soil temperatures exceed 55°F (13°C)
- Harvest: late spring continuously until first frost
Hardiness
USDA hardiness zones: 9–11
Temperature: down to -7°C
Troubleshooting
Most calibrachoa trouble comes back to soil pH, watering, or light, and it reads plainly in the leaves and the flowering. Catch the early signs and you can pull a plant back before it slides. Match what you see below, then act while there is still time to help.
Stems brown and slump at the base in soaking-wet mix
A plant that flops while the mix is still wet through is telling you the roots have failed, usually to root or stem rot driven by Pythium or Phytophthora. Tip it out and read the roots with your fingers: living ones are pale, white, and firm to the touch, while rotted ones turn brown, go soft and mushy, and thin out to just a few strands. A badly struck plant will not recover, so discard it and move any firm-rooted survivors into fresh, fast-draining mix in a pot that truly drains.
Fix:
- Stop watering until the top of the mix dries
- Remove and discard badly affected plants
- Replant survivors in fresh, fast-draining mix in a container with working drainage holes
Newest leaves pale to yellow while the veins stay green
Look at the youngest leaves: when the blade washes out to yellow but the fine veins hold a clear green tracery, you are seeing iron deficiency. It strikes the new growth first because this plant draws down more iron than most bedding flowers. The usual cause is potting mix that has crept past pH 6.5 and locked the iron away from the roots. Test it, ease the pH back toward 5.5 to 6.0 with iron sulfate, and drench with chelated iron to flush green back into the fresh leaves.
Fix:
- Lower the media pH toward 5.5 to 6.0 using iron sulfate per label directions
- Drench with chelated iron to green up new growth
- Resume feeding every other week with a balanced water-soluble fertilizer
Sticky leaves, speckled blades, or warped new shoots
A tacky film on the leaves, a finely speckled or bleached blade, or fresh shoots that come in crumpled all point to aphids, thrips, or spider mites, the three pests that find calibrachoa most often. Turn the shoot tips and leaf undersides over and look closely for clustered aphids, faint webbing strung between leaves, or slim thrips that bolt when you tap a stem above a sheet of white paper. A hard jet of water dislodges most of them, and insecticidal soap or horticultural oil clears the stragglers.
Fix:
- Knock pests off with a strong spray of water
- Treat infestations with insecticidal soap or horticultural oil per label
- Discard heavily infested stems
Thin bloom on long, bare, stretched stems
Stems that stretch long and bare with few flowers along them are almost always short on light, since bloom thins out as shade deepens. Skimpy feeding compounds it, because this is a hungry plant that stalls without steady meals. Shift the container into full sun, snip the leggy tips back about 2 in (5 cm) to wake up fresh side branches, and feed every other week.
Fix:
- Move containers to a spot with full sun
- Trim back leggy stem tips by about 2 in (5 cm) to force branching
- Feed every other week with a balanced water-soluble fertilizer
Toxicity
Good news for pet owners and parents: calibrachoa is safe to keep around the whole household. It stays off the ASPCA toxic plant lists, and its close cousin the petunia is listed as non-toxic. The worst a curious nibble brings is a mild, passing stomach upset, the kind any plant can cause.
Safe for
People · Cats · Dogs · Horses · Rabbits · Livestock · Birds
Cats None
Fine to grow where cats roam. It never makes the ASPCA toxic list, and a stolen nibble of leaf or flower brings nothing worse than the brief stomach upset any plant might trigger.
Dogs None
Dogs are in the clear as well. A dog that chews on a trailing stem might rumble a little from the fibrous mouthful, but no toxin is at play here.
Horses Safe
Horses can graze right beside it unharmed. The plant holds nothing known to poison them.
Rabbits Safe
Rabbits take no harm from the leaves or flowers, and a few chewed stems do nothing more than top them up.
Livestock Safe
Cattle, goats, and sheep are safe around it, since the plant carries no compounds that bother grazing animals.
Birds Safe
Pet and garden birds come to no harm near the blooms. There is no need to screen the baskets away from them.
People Safe
Harmless to people, though it is an ornamental and not a plant grown for the plate. Children playing close by face no danger from it.
No special handling precautions are needed
Varieties
Calibrachoa reaches gardeners as a small set of named series rather than stand-alone varieties. These are the ones worth knowing by name.
Million Bells
The first trademarked series, it carried calibrachoa into US gardens during the 1990s and lent the plant the everyday name people still use.
Superbells
A strong-growing trailing series flowering in solid, double, and patterned forms that stands up well across university trials.
MiniFamous
A series prized for its double blooms, with named picks like Uno Yellow and Uno Pink Star that extension horticulturists point to.
Cabaret
A tight, even-growing series built for hanging baskets and mixed pots that scores well in extension trials.
Callie
A semi-trailing series carrying the plant's extension nickname callie and flowering in baskets right through the season.
How to propagate
Calibrachoa is increased from cuttings rather than seed, though patents put real limits on doing it yourself.
Stem cuttingsModerate
Spring to summer
Cuttings are the workable route to more calibrachoa, since the plants set very few seeds. Take them in spring or summer from healthy growing stems. One thing to keep in mind: most named cultivars are patented, so propagating them at home is not legally allowed.
Myths
You have to pinch off spent flowers like you do with petunias to keep calibrachoa blooming.
The blooms are self-cleaning, dropping away on their own once they fade, so there is nothing to pluck off to keep the display going. It flowers from spring until frost with no deadheading at all.
Calibrachoa is really just a tiny petunia you can raise from saved seed.
It stands as its own genus, not a shrunken petunia, and it sets very few seeds. Nearly every garden hybrid is raised from cuttings instead. Most cultivars are patented, so propagating them at home is off limits.
Yellow leaves on calibrachoa are always a sign of overwatering.
When the yellow lands on the new growth and the veins stay green, the cause is usually iron deficiency from a media pH that has climbed too high. This plant needs more iron than most bedding flowers and does best in a slightly acidic mix around pH 6.0.