Kalanchoe, is a tropical genus of around 125 succulent species from the stonecrop Crassulaceae family. While they are mainly indigenous to Madagascar and Africa, a few are found in China and south-eastern Asia. The genus was first described in 1763 by Michel Adanson, a French botanist. The name comes from the Chinese name “Kalan Chauhuy”. A mature plant was sent into space to the Salyut 1 Soviet space station in the late 1970s.
Most species are herbaceous perennials or shrubs, with a few annual plants or some that last for 2 years. The largest is K. beharensis from Madagascar is the tallest species at 20 feet in height, but generally, most are 3 feet high or less.
The flowers come in various colors of yellow, dark red, pink, orange, gold, or white and need short days and 14 – 16 hours of darkness for flower buds to develop – this naturally occurs from October to February.
However, this can be simulated for indoor plants by keeping them in a room or closet where lights are turned off during the night and on again in the morning for about six or more weeks. After flower buds are visibly large enough, controlling light is no longer essential and the plants can be placed anywhere. Flowering should begin about 12 weeks later in January. These plants are cultivated as indoor ornamentals and succulent or rock garden plants.
These plants grow best in indirect bright sunlight. They can handle some exposure to full sunlight provided that they have shade to protect them from direct afternoon sunshine. They grow well indoors in indirect bright light although their flower buds won’t open and they will get leggy when growing under insufficient light. Don’t grow them near windows that get bright afternoon light as their leaves can get scorched and flower production will be reduced.
These plants can suffer damage if over-watered as they store water in their leaves and stems. This means that they should be watered every fortnight, although other aspects such as temperature, lighting, and pot size should be considered, particularly in warm climates. They might need weekly watering when they are flowering but they should have good drainage.
These plants are not picky about humidity levels. They can handle humidity levels between 75 – 85%. However, prolonged humidity above 90% can lead to leaf drop, leaf spot, or damage to buds and flowers. They don’t require misting or spraying but if the foliage is very dusty, give the plants a good wash once a year.
Ideal temperatures for these plants are between 40 – 70°F. Average indoor temperatures are fine. Cool temperatures at night prolong flower life while temperatures over 80°F can result in “heat delay” and inhibit bud development. The best temperatures for bud development are 40 – 45°F at night and 60°F in the day. They can handle different temperatures, provided that they are not exposed to frost.
These succulents grow best in aerated, well-draining soil. A combination of ½ succulent/cactus mix and ½ potting soil with a little compost is good enough. Regular potting soil can also work but it’s difficult to keep it dry enough. Sprinkle earthworm compost on the topsoil when you plant.
These plants thrive better when they are frequently repotted as this encourages good drainage. For optimum growth, repot them annually in autumn after the flowers die — this encourages new growth and health. Go up one pot size every time you repot. Use well-draining pots – clay pots are good since they allow excess water to evaporate from their porous sides as well. Replace the soil with fresh succulent/cactus mix.
You can propagate these plants by seed, stem cuttings, or division.
Propagation from seed
While these plants are typically grown from cuttings, producing faster results, they are also rather easy to grow from seeds. Seeds are sown on the top of succulent/cactus mix in spring – don’t cover the seeds, as light is needed for the germination process. Use a tray or small containers and cover with plastic film to increase humidity levels until they germinate, after about 10 days. Seedlings can be transferred to individual containers or outdoors two months after germination.
Propagation by cuttings
Take 4 – 5 inch long stem cuttings, with the lower leaves a few leaves removed, and then keep them for one week or so for the cut ends to callus. A 6 to an 8-inch container with succulent/cactus mix can be used to grow several cuttings. Keep the cuttings under indirect light after planting. They’ll take root in around 3 weeks, do not mist the leaves while they’re rooting.
Propagation by division
Division can easily be done if you have multiple plants growing in 1 pot. Separate the plant, each having a set of stems and roots, and plant them in succulent/cactus mix in containers or outdoors.
The last two techniques should be undertaken in spring or summer when the plant isn’t flowering.
Top dress the soil with organic compost or worm castings and compost every spring. Any houseplant fertilizer can be used once a month instead of compost. Fertilize actively growing plants with any houseplant fertilizer. Don’t over-feed the plants because salt build-up can scorch the roots, visibly showing up as brown spots on leaves. Avoid fertilizing plants that are stressed from under- or over-watering.
These plants tend to get gangly over time and need to be pinched back after flowering to keep them compact. Cut down tall stems and spent flower stems. Bring them indoors 3 months before the flowering season starts or before the first predicted frost. When the danger from frost has passed, they can be moved outdoors.
Plant diseases are seldom a problem when they grow indoors but problems can crop up when they are watered incorrectly or if they undergo temperature extremes.
Plants touched by frost or near-freezing temperatures often suffer leaf damage or stunted flowers. To help them stay healthy and grow well, keep them in temperatures above 50°F.
High temperatures above 80°F will cause foliar wilt and “heat delay” that affects bud formation. Keep these plants ideally in temperatures between 40 – 70°F.
These plants can get affected by extreme light exposure. Insufficient light will affect the glossy green color of the foliage and excessive direct sunlight will cause leaf scorch.
One very common problem is soil that retains water together with over-watering. This easily causes stem and root rot. Stop watering if you notice this problem developing and repot the plants after the soil has become dry into fresh succulent/cactus mix.
Powdery mildew is another potential problem. It shows up as leaf mottling, yellow spotting, lines or ring patterns, or dead flecks and generally happens under high humidity. Plants might become stunted and stop flowering. Allow the plants to have plenty of air circulation. Treat the infection with fungicide and remove badly damaged foliage.
Brown scale, mealybugs, and aphids are some common pests of these plants. The infected plants should be isolated. Mealybugs can be controlled by wiping them with cotton saturated with alcohol. Aphids are removed by a water spray or by hand scraping brown scales off the foliage.