Plectranthus is a large genus of about 85 species of plants native to the tropical areas of the Southern Hemisphere. Plectranthus are in the same family as mint (Lamiaceae). Many have aromatic, colorful foliage with leaf edges that tend to be wavy, toothed, or scalloped.
Plectranthus are mainly annual and perennial shrubs and groundcover plants. These plants are versatile; most grow well in-ground, in containers, and as houseplants. They are best planted in the spring, or you can sow seeds indoors six weeks before the last frost.
As Plectranthus is a fast-growing, low-maintenance species, some species are invasive, like P. amboinicus (Indian borage). Also, some species are toxic to animals; for example, Indian borage is also toxic to dogs, cats, and horses.
|Common Name||Spur flower|
|Botanical Name||Plectranthus spp.|
|Plant Type||Annual and perennials; herbaceous groundcovers and shrubs|
|Mature Size||6 inches to 6.5 feet tall|
|Sun Exposure||Full sun or partial shade|
|Bloom Time||Spring, winter, fall|
|Flower Color||Purple, pink, white, and blue|
|Hardiness Zones||8 to 11 (USDA)|
|Native Area||Africa, Asia|
|Toxicity||Some Plectranthus species are toxic to dogs, cats, and horses.|
Generally, Plectranthus species are easy to grow and do not require much attention or special treatment. They do best in locations that provide partial shade, although some species can grow in full sun. Plectranthus are not frost-tolerant, but the perennial species will come back in the spring in cold winter locations.
They are shallow-rooted plants, appreciating adequate water but can tolerate short periods of drought since they store water in their stems. They are easily propagated and only require pruning for cosmetic reasons.
Some Plectranthus species are considered invasive. According to CABI (formerly known as the Center for Agriculture and Bioscience International), P. amboinicus (Indian borage) is invasive in Cuba and the Pacific Islands. Plectranthus ciliatus and P. barbatus are two invasive species in South Africa.
The exact amount of light needed to grow Plectranthus depends on the species. Very few can tolerate direct sun and may suffer from leaf burn if exposed to direct sun for too long. However, most Plectranthus appreciate bright, indirect light as a general rule of thumb. When growing Plectranthus outdoors, choose a spot that receives sun for only part of the day or a shady spot beneath a tree. When grown indoors, you can put the plant in a location that receives direct light for most of the day.
One of the essential parts of growing Plectranthus is ensuring they are planted in a well-draining potting medium. Standard potting soil mixed with perlite or sand should provide adequate drainage. Plectranthus do not tolerate "wet feet," which means their roots cannot sit in wet or soggy soil for prolonged periods.
Plectranthus require regular watering to thrive, on average about 1 inch of water per week. Only water once the top inch or two of soil has dried out. Be careful not to overwater. The soil should stay moist but not wet. It is important to note that water needs may vary from species to species.
Temperature and Humidity
While Plectranthus is not a frost-tolerant genus, plants in this genus do well in colder temperatures and even flower during the shorter days of the year. Since the Plectranthus genus comprises both annual and perennial species, the exact temperature requirements vary from species to species.
Plectranthus does not tolerate temperature extremes well. Most plectranthus can't handle cold temperatures for long periods but can take rare days that drop down to 10 degrees Fahrenheit. In sweltering climates, Plectranthus may struggle and require extra care (watering and shade) to survive.
Plectranthus species prefer average to above average humidity from 50 percent up to 80 percent relative humidity.
Plectranthus plants appreciate monthly fertilization during their active growing period, from the spring to the fall. A standard 10-20-10 plant fertilizer should be sufficient for most varieties.
Types of Plectranthus
Among the best-known Plectranthus species is Swedish ivy, also called creeping Charlie, and a hybrid Plectranthus called 'Mona Lavender,' a popular houseplant. Coleus is a common plant recently reclassified from the Plectranthus genus to stand as its own genus.
- Plectranthus amboinicus (Mexican mint or Indian borage)
- Plectranthus 'Mona Lavender'
- Plectranthus barbatus (Blue spur flower)
- Plectranthus verticillatus (Swedish ivy or creeping Charlie)
Species in the Plectranthus genus can be pruned regularly to help them maintain an attractive shape. Shrubby varieties look best when cut back and shaped into more dense bushes. Ground cover varieties grow quickly and may be pruned regularly to prevent overgrowing.
Plectranthus are easily propagated through division and cuttings. The best time to propagate is during the spring or early summer. For example, the blue spur flower is an aggressive spreader, sending out offshoots under the soil. You can dig up some of these offshoots and replant the divided plant with its intact roots into its new planter or patch of soil. Here's how to divide:
- You will need well-draining soil, a pot or planting location in partial light, a hand trowel, and, optionally, some pruning snips.
- Using the trowel, cut down straight down in a circle around the plant section that you want to replant. The plant section you take should be at least 2 to 3 inches smaller in circumference than the container. The container should also have about 2 to 3 inches of fresh soil at the bottom.
- Pruning snips can come in handy, helping you cut through straggling roots, if necessary.
- Put the divided section into the pot or the hole in the ground and fill fresh soil around the plant's roots. Water the plant.
Another option for propagation is to use stem cuttings. The cuttings root easily in soil and can be grown without much hassle. Here's how:
- You'll need sterile, sharp garden snips or scissors, well-draining soil, and a pot or planting location in partial light. Cut a section from your plant at least 3 inches in length. Make sure the stem has at least five leaf nodes.
- Remove the bottom leaves. Leave the topmost two sets intact.
- Place your cutting, cut-end down, in damp soil. Keep it moist while rooting. It can take 2 to 3 weeks to root.
- Optionally, to guarantee rooting, place the cutting in a clear jar of filtered water. While waiting for the roots to form, replenish the filtered water every few days to keep the water line consistent. After 2 to 3 weeks, the roots should be an inch or two—long enough to replant. Plant the stem cutting and its new roots about an inch deep in the new pot or in the ground. Fill fresh soil around the plant's roots. Water the plant.
How to Grow Plectranthus From Seed
You can start seeds 6 to 8 weeks indoors before the last frost in the spring. You'll need seed starting soil, seed starting trays, or small cups. Plant the seeds shallowly, about 1/8 to 1/4 inch deep. Keep the soil moist and warm (room temperature from 70 to 75 F). Provide bright light for at least 8 to 16 hours. The plants need at least 8 hours of dark to grow. Seedlings should emerge in 7 to 14 days.
Repot in about 6 to 8 weeks after the seedling emerges. You can repot in the ground as long as the last threat of frost is gone. Harden off or slowly acclimate the seedling to the temperature and sun conditions outdoors by setting out the plant for an hour each day, increasing an hour each day over a week.
Potting and Repotting Plectranthus
Plectranthus needs to drain adequately after watering. Select any container as long as it has ample drainage holes. If transplanting as a seedling, plant the seedling in a 4 to 6-inch pot. If repotting from a smaller pot, make sure the new pot is at least 2 inches larger in diameter and has at least 2 inches of fresh soil at the bottom of the new container. Center the transplant in the pot and fill fresh soil around it. Water thoroughly until water drains out of the base.
In cold climates or snowy winters, Plectranthus will dieback but may come back in the warmer spring months, depending on the species. Some gardeners choose to move their Plectranthus plants indoors for the cold winters, which allows them to survive throughout the year.
Before a Plectranthus experiences dieback outdoors, snip off a few succulent, young stems with several leaves. Root the cuttings in filtered water on a windowsill. Remove the leaves that are below the waterline. As the waterline recedes, replenish the water. Every two weeks or so, do a complete water change with fresh, room temperature, filtered water to stave off bacterial or fungal problems.
Common Pests & Plant Diseases
Pest problems rarely affect Plectranthus; however, whiteflies, aphids, and red spider mites can sometimes strike during the summer months. You can try organic treatments or environmentally less invasive remedies like insecticidal soap or neem oil to remove the infestations.
This plant is susceptible to fungal diseases like leaf spot, stem rot, and root rot. Leaf spot is often caused by leaves getting wet and staying that way. Poorly drained soils or containers with inadequate drainage are usually the main reason for root and stem rot. It's best to water plants in the morning and at the soil line and not directly on the foliage.
You can try a fungicide treatment and follow the package instructions to treat these fungal diseases. Also, remove damaged leaves to prevent spores from spreading.
How to Get Plectranthus to Bloom
Plectranthus plants flower multiple times a year, flowering mainly at the end of the season, during the year's shortest days in winter-hardy zones, or in cool summer climates. If you wonder why your plants are not blooming, make sure your plants get no more than 12 hours of light since day length affects flowering. Pruning and deadheading faded flower spikes will likely encourage more blooms.
Depending on the species, the flowers can be purple, pink, white, or blue. Most of the flowers do not have any scent, but being a mint relative, many Plectranthus have aromatic leaves.
Common Problems With Plectranthus
Plectranthus is not known for having many problems, but sometimes it can attract a few pests and fungal issues. It's important to recognize signs that your plant is having some issues.
If you notice lower leaves of a plant turning yellow, falling off, and wilting, this may be a sign of root rot. If watering doesn't perk up your plant, you likely have root rot. Pull up the root ball and inspect the roots. If most of the plant's roots have blackened, discard the plant. Using a sharp, sterile knife cut away any blackened, rotting roots and apply a fungicide. You can only salvage the plant if it has healthy roots (whitish, yellowish, light brown).
Yellowing leaves can also occur if the plant gets too much sun. Sunburn can cause leaves to curl, turn brown, and dry up. Move the plant to a shadier spot to prevent leaves from getting scorched.
If your plant is wilting, try giving more water. If your plant does not recover when you water it, it's likely root rot.
Plectranthus leaves can turn brown if the plant gets too much water or direct sun, lacks nutrients, or is attacked by pests. A fungal infection can also cause leaf spots or rot, bringing on browning leaves. Check the water, light, and fertilizer and inspect the leaves and stems for insect activity. If necessary, adjust any of those factors accordingly.
How long can Plectranthus live?
Most Plectranthus live about 5 years on average.
What plant is an alternative to Plectranthus?
Plectranthus 'Mona Lavender' is an excellent alternative to common lavender if you have pets. Common or English lavender is toxic to cats, dogs, and horses; meanwhile, 'Mona Lavender' is a non-toxic plant with equally beautiful, similar-looking flowers that bloom over a long period.
Can Plectranthus be grown indoors?
Most plectranthus can grow indoors with ample sunlight, such as a southern exposure. Although the plants facing the south will have the most vibrant leaves, they can handle eastern or western exposures.
Invasive Species Compendium: Plectranthus amboinicus(Indian borage). CAB International.
Indian borage. ASPCA.
Plectranthus argentatus. NC State Extension.