Calibrachoa, also known as million bells, is one of the most popular plants for growing outdoors in containers. Although it is a short-lived perennial in very warm climates, it is grown almost everywhere as an annual. It has a trailing habit and looks great in hanging baskets, bowls, or mixed containers. Calibrachoa also works well in unusual containers, such as colanders or even plastic laundry baskets. Calibrachoa is a prolific bloomer and produces 1-inch blossoms that resemble tiny petunias.
Calibrachoa is not recognized as a separate genus by some authorities. The Royal Horticultural Society, for example, views them as a variety of petunia, giving them the name Petunia 'Million Bells'.
Calibrachoa comes in a rainbow of colors, in solids and two-tones, stripes, patterns, and stunning double blooms. The compact leaves are oval-shaped and a bit sticky. In most growing zones, million bells is best planted or repotted in spring. It can bloom continuously through the growing season, and its flowers attract butterflies and hummingbirds. It's also a fast grower and quickly reaches toward the ground as a "spiller" when grown as a container plant.
|Botanical Name||Calibrachoa group|
|Common Name||Calibrachoa, million bells, trailing petunia, mini petunia|
|Plant Type||Herbaceous perennial flower often grown as an annual|
|Mature Size||6–12 inches tall, 12–24 inches wide|
|Sun Exposure||Full sun to part shade|
|Soil Type||Moist, rich, well-drained|
|Soil pH||5.0–6.5 (acidic)|
|Bloom Time||Spring to fall|
|Flower Color||Coral, yellow, orange, red, pink, blue, purple, burgundy, lavender, cream|
|Hardiness Zones||9–11 (USDA); grown as an annual in all zones|
|Native Area||South America|
Million bells plants have simple demands: They require sunlight, enough water, and food. The plant is not hard to care for, but paying attention to its needs will keep it blooming from spring well into fall. While they can be planted in garden beds, they fare much better in containers.
This is considered a “self-cleaning” plant, meaning it doesn’t need to be deadheaded to keep blooming; however, it will benefit from a serious cutting back toward the end of summer.
These plants bloom best with at least six hours of full sun, but they can tolerate partial shade—especially in warmer areas, where plants that get some shade are likelier to survive through the summer months. Insufficient sun exposure typically results in reduced blooming.
Calibrachoa plants like fast-draining potting soil, so make sure your pot has good drainage. When planting in garden beds, amend with organic material to ensure richness, and make sure the soil drains well. Mulch is recommended to keep the soil moist and the root system cool.
Calibrachoa needs to be kept well hydrated but not water-logged. Add water only after the top inch or so of the soil dries out. To check if your plant needs water, stick your finger into the soil up to the second knuckle. If the soil feels dry at your fingertip, water deeply until it drains out of the bottom of your pot. Don’t water again until the soil dries out again.
Heat, wind, and lack of humidity can cause your soil to dry out quickly. Depending on your conditions, you may have to water as often as twice a day. Check the soil frequently, especially at the beginning of the season, until you get to know your plants’ needs; watering requirements may change as the summer heats up. Take care not to overwater these plants, as this can encourage root rot.
Temperature and Humidity
These plants are pretty drought- and heat-tolerant, and even cold-tolerant, but to get the best blooms, don’t let them dry out repeatedly. They prefer temperatures between 55 and 65 degrees Fahrenheit. Hardened-off plants can be brought outdoors in the spring months; most can tolerate a mild frost. At the other end of the spectrum, hot weather and dryness can be stressful to the plants. You can revive wilted foliage with a daily misting; just be careful not to mist in direct sun, as this can burn the leaves.
This plant is a heavy feeder that can be fed with a slow-release fertilizer and/or a diluted liquid fertilizer regularly. For example, you can start with an organic, slow-release fertilizer mixed into your potting medium, and then give the plant a diluted liquid every couple of weeks throughout the season. Feeding is particularly necessary near the end of the season to promote late blooms. Be careful not to over-fertilize—follow the directions on the label of the plant food closely. Leaves turning light green or yellowish is a sign that the plant needs fertilizer, or possibly more sun.
Varieties of Calibrachoa
There are 28 different species in the Calibrachoa genus, but those used for garden cultivation are generally complicated hybrids derived from crossing various species. There are dozens of varieties of Calibrachoa available in a vast array of colors, including:
- Calibrachoa 'Cabaret Hot Pink': produces loads of bright pink flowers on trailing stems up to 8 inches long
- C. 'Cabaret Purple Glow': grows 12 inches wide and trails to 8 inches
- C. 'Million Bells Terra Cotta': orange flowers streaked with red and gold on stems trailing to 8 inches
- C. 'MiniFamous Double Blue': double flowers of deep blue-purple on a trailing plant with 10-inch-long stems
- C. 'Superbells Pomegranate Punch': velvety-red flowers that get darker toward the center; grows 8 inches tall
- C. 'Kabloom': a series of hybrid plants that can be grown from seed; available in pink, white, red, yellow, and deep blue
Potting and Repotting Calibrachoa
Most million bells plants are badly root-bound when you buy them—so much so that there is very little soil left in the pot. This means that your margin of error for watering is very slim and there isn’t much nutrition for the plants to use. When you pot the plant, be sure to loosen the root ball and add a slow-release fertilizer into a general-purpose potting mix.
These are short-lived plants that don't require repotting.
Calibrachoa plants grown in gardens are hybrids that produce few seeds. And because many of the varieties are trademarked hybrids, vegetative propagation through cuttings is technically illegal. If you do attempt to propagate through cuttings, the process is as follows:
- Try to find a stem that has small buds but no flowers on it. Cut off the stem at least 6 inches from the tip, then remove any lower leaves.
- Place your cuttings in an equal mix of half potting soil and half peat moss. Water well.
- Set the pot under bright light, and keep the cuttings moist and warm (about 70 degrees Fahrenheit). Roots should begin to develop within a couple of weeks.
Root rot or mold infection can set in if these plants are overwatered. (Plants that wilt after watering may be suffering from root rot.) Calibrachoa plants are also susceptible to spider mites and aphids. Prevention in the form of good air circulation, proper water management, and good soil porosity is the best defense. It can also help to wait a while to plant, putting them in the ground around the same time you'd plant tomatoes; planting early can lead to aphid problems.
Deer don't seem very interested in Calibrachoa plants, although they are not classified as deer-resistant.