Plectranthus ‘Mona Lavender’ thrives with bright indirect light, well-drained soil, consistent moisture, and protection from frost. Developed in the late 1990s at South Africa’s Kirstenbosch National Botanical Garden, this hybrid between Plectranthus saccatus and Plectranthus hilliardiae has become one of the most popular ornamental plectranthus varieties worldwide, largely because of its striking tubular lavender flowers and deep purple leaf undersides. Despite its lush, tropical appearance, it is surprisingly easy to grow once you understand a few key preferences, especially its relationship with light.
Where It Comes From and Why That Matters
Mona Lavender’s parentage traces to the forest understory of eastern South Africa, where both parent species grow beneath tree canopies in dappled shade. That ancestry tells you most of what you need to know about its care: it wants warmth, humidity, protection from harsh midday sun, and soil that drains freely. The plant was bred specifically as an ornamental, selected for its prolific flowering, compact habit, and the dramatic contrast between its glossy dark-green upper leaves and rich purple undersides. It was named Plant of the Year by the South African nursery industry shortly after its release and quickly gained fans in subtropical and temperate gardens around the world.
Light Requirements and How They Affect Flowering
Light is the single most important factor in getting Mona Lavender to perform well. The plant needs bright, filtered light for strong vegetative growth, but too much direct sun will bleach or scorch the leaves. A spot with morning sun and afternoon shade, or consistent dappled light throughout the day, is ideal. Indoors, an east-facing window or a position a few feet back from a south- or west-facing window works well.
Flowering is a separate issue from general growth, and it hinges on day length. Mona Lavender is a short-day plant, meaning it initiates flower buds when the number of daylight hours drops below a certain threshold. Research on plectranthus flowering found that plants kept under 16-hour days never budded at all, staying entirely vegetative. The quickest flowering occurred under 12-hour days, while plants given 14-hour days bloomed about two weeks later and grew a few inches taller before setting buds. Plants under very short 10-hour days flowered at roughly the same time as the 12-hour group but produced lower-quality growth because there was not enough total light each day to build strong stems and foliage.1Greenhouse Product News. Blooming Plectranthus — A Study on Flowering
In practical terms, this means Mona Lavender typically blooms in autumn and winter outdoors, when natural day lengths fall to around 12 hours or less. If you grow it indoors under artificial lights that stay on for 16 hours, you may get a gorgeous bushy plant that never flowers. If you want blooms, either place the plant where it experiences naturally shortening days, or deliberately limit its light exposure to about 12 hours per day starting in late summer.
Soil and Potting
Mona Lavender does best in a loose, well-draining growing medium rich in organic matter. A standard high-quality potting mix amended with perlite or coarse bark works well. If you are planting directly in the garden, work compost into the planting hole to improve drainage and fertility. The plant is not fussy about pH but performs best in slightly acidic to neutral soil, roughly in the 5.5 to 6.5 range.
In containers, make sure the pot has drainage holes. Mona Lavender roots rot quickly in waterlogged soil, and sitting in a saucer of water for more than an hour or two after watering is enough to cause problems. Terracotta pots are a good choice because they wick away excess moisture, though they also dry out faster in hot weather, so you will need to water more often during summer.
Repotting every one to two years keeps the plant healthy. Mona Lavender is a vigorous grower and can become rootbound in a single season. When roots start circling the bottom of the pot or poking out of drainage holes, move it to a container one size up. Spring is the best time for repotting, giving the plant a full growing season to establish in its new space.
Watering
Keep the soil consistently moist but never soggy. The best approach is to water thoroughly when the top inch or so of soil feels dry to the touch, then let the excess drain away completely. During the active growing season from spring through autumn, this might mean watering every few days indoors or every day or two in hot outdoor conditions. In winter, growth slows and the plant needs less water. Reduce your frequency but do not let the soil dry out completely, as wilted Mona Lavender recovers slowly and the lower leaves often drop permanently.
If the leaves start looking limp and the soil is wet, overwatering is the likely culprit. Back off, let the soil dry more between waterings, and check that your drainage is adequate. If the leaves look limp and the soil is dry, you simply need to water more often. The plant gives you readable signals once you learn to distinguish the two scenarios.
Temperature and Hardiness
Mona Lavender is frost-tender. It grows as a perennial outdoors in USDA hardiness zones 9 through 11 and can handle brief dips to about 2°C (35°F) without serious damage, but a hard freeze will kill it. In cooler climates, grow it as a container plant that moves indoors for winter, or treat it as an annual. Many gardeners in zones 7 and 8 bring it inside when nighttime temperatures start falling below 10°C (50°F) in autumn.
Indoors, normal household temperatures between 18°C and 27°C (roughly 65–80°F) suit it well. Avoid placing it near cold drafts from windows or doors in winter, or directly in the path of heating vents, which will dry the air around the foliage and stress the plant. Mona Lavender appreciates moderate to high humidity. If your home is dry in winter, grouping it with other plants, setting the pot on a tray of wet pebbles, or running a humidifier nearby all help.
Heat deserves a mention too. Temperatures above about 32°C (90°F) can slow growth and delay flowering. Research on plectranthus flowering noted that heat during bud initiation and development reduced flower quality, even when day length was otherwise correct for blooming.1Greenhouse Product News. Blooming Plectranthus — A Study on Flowering So if you are growing Mona Lavender in a hot climate, try to keep it in a cooler, shaded spot during the peak of summer and count on the best blooms coming as temperatures moderate in autumn.
Feeding
Mona Lavender is a moderately heavy feeder during its active growth phase. A balanced liquid fertilizer applied every two to three weeks from spring through early autumn keeps it growing vigorously and supports flower production. Many growers switch to a fertilizer slightly higher in phosphorus in late summer as the plant approaches its flowering period, which can encourage more prolific blooms, though this is not strictly necessary if the plant is well-nourished overall.
Stop fertilizing in winter if growth has slowed significantly. Feeding a plant that is not actively growing leads to salt buildup in the soil, which can burn roots over time. If you notice a white crust forming on the soil surface or around the rim of the pot, flush the soil with plain water several times to wash out accumulated salts before resuming fertilization in spring.
Pruning and Shaping
Regular pruning is one of the secrets to a good-looking Mona Lavender. Without it, the plant tends to get leggy and floppy, especially in lower light. Pinching the growing tips back by a couple of nodes every few weeks during spring and summer encourages branching and produces a denser, bushier plant with more potential flowering sites come autumn.
After the flowering period ends, give the plant a harder prune, cutting stems back by about a third to a half. This removes spent flower spikes and reshapes the plant for the next growing season. Mona Lavender responds well to even fairly aggressive pruning and will push out new growth readily from lower nodes. Do not be timid with it. A plant that has been allowed to get tall and bare at the base is harder to rehabilitate than one that gets pruned regularly throughout the year.
Save your pruned stem tips for propagation, which leads to the next topic.
Propagation from Stem Cuttings
Mona Lavender is one of the easiest plants to propagate from cuttings. Take tip cuttings about 8 to 10 centimeters (3–4 inches) long, strip the lower leaves, and insert the stems into a moist mix of perlite and peat (or just a glass of water, which works too). Roots typically appear within one to three weeks. Once cuttings have a healthy cluster of roots a few centimeters long, pot them up into individual containers with regular potting mix.
Spring and early summer cuttings root fastest because the plant is in active growth mode. Autumn cuttings taken after flowering will also root but may take longer. Rooting hormone is helpful but not essential; the plant roots readily without it. If you are rooting in water, change the water every few days to prevent bacterial buildup. Once potted, keep newly rooted cuttings in bright indirect light and maintain even moisture until you see new top growth, which signals that the roots are established.
Because Mona Lavender is a hybrid, it does not come true from seed. Stem cuttings are the standard way to produce new plants that are genetically identical to the parent. Seeds, if they form at all, will produce unpredictable offspring that may not resemble the parent plant.
Common Pests and Problems
Mona Lavender is relatively pest-resistant compared to many houseplants, but a few issues come up regularly:
- Mealybugs: These white, cottony insects cluster in leaf axils and along stems. Wipe them off with a cotton swab dipped in rubbing alcohol, or spray with insecticidal soap. Persistent infestations may need a systemic insecticide.
- Spider mites: Tiny and hard to see, spider mites thrive in hot, dry conditions. Fine webbing on the undersides of leaves is the giveaway. Increase humidity around the plant, spray the foliage with water regularly, and treat with insecticidal soap or neem oil if the population builds.
- Whiteflies: Small white insects that fly up in a cloud when you disturb the plant. Yellow sticky traps near the plant catch adults, and insecticidal soap handles the nymphs on the leaf undersides.
- Root rot: Almost always caused by overwatering or poor drainage rather than a specific pathogen. Prevention is the main treatment here. If a plant is already showing signs of rot, such as mushy brown roots and persistently wilting foliage, remove it from the pot, trim away all rotted roots, and repot in fresh, well-draining mix. Water carefully going forward.
Leaf drop on the lower stems is common and not always a sign of trouble. As the plant grows upward, older lower leaves naturally yellow and fall. If the dropping is sudden and widespread, check for overwatering, underwatering, temperature shock, or a recent change in light conditions.
Growing Mona Lavender Outdoors
In frost-free climates, Mona Lavender makes an excellent landscape plant for shaded beds, borders, and containers on covered patios. Plant it in partial shade beneath trees or on the east side of a building where it gets morning light and afternoon protection. It pairs well with ferns, impatiens, and begonias, sharing similar light and moisture needs.
Outdoor plants can grow larger than indoor specimens, reaching 60 to 90 centimeters (2–3 feet) tall and about as wide. They still benefit from regular pinching during the growing season to stay compact. In subtropical regions, Mona Lavender may bloom for an extended period from late summer well into winter, putting on a spectacular show when many other plants have finished flowering for the year.
In areas with mild but occasional frosts, planting against a south-facing wall or under an overhanging eave can provide just enough protection to get through cold snaps. Mulching around the base with a thick layer of organic material insulates the roots. If the top growth is damaged by frost, cut it back hard in spring and the plant will often regenerate from the base.
Growing It Indoors Year-Round
Mona Lavender adapts well to indoor life, which is how most people in temperate climates grow it. The main challenge indoors is getting it to flower. As discussed earlier, the plant needs short days to initiate buds. If your indoor space has artificial lighting on in the evening, even ambient room light from lamps or screens, the plant may perceive a longer day than the actual outdoor photoperiod and stay vegetative.
The workaround is simple: move the plant to a room that gets no artificial light after sunset during the autumn months. A guest bedroom, an unheated porch, or even a closet for the dark period can work, as long as the plant gets adequate natural light during the day. About eight to ten weeks of consistent short days (roughly 12 hours of light or less) should trigger bud formation. Once buds are visible, you can move the plant back to your main living space to enjoy the flowers without worrying about extending the photoperiod.
Aside from the light question, indoor care is straightforward. Rotate the pot a quarter turn every week or two so growth stays even on all sides. Clean the leaves occasionally with a damp cloth to remove dust, which improves both the plant’s appearance and its ability to photosynthesize. And keep it away from pets that like to chew plants. While plectranthus species are not considered highly toxic, ingestion can cause mild gastrointestinal upset in cats and dogs.
Why Mona Lavender Sometimes Refuses to Bloom
This is the single most common frustration people report with the plant, and the answer almost always comes back to light. If your Mona Lavender grows beautifully but never flowers, run through this checklist:
- Day length too long: The plant is getting more than about 14 hours of light (including artificial light in the evening). Reduce the photoperiod.
- Too much nitrogen: Heavy feeding with a high-nitrogen fertilizer promotes leafy growth at the expense of flowers. Switch to a balanced or bloom-promoting formula.
- Recent hard pruning: If you pruned heavily in late summer, you may have removed the stems that were about to set buds. Time major pruning for after flowering or early spring.
- Heat stress: Persistently high temperatures during what should be the bud-initiation period can delay or prevent flowering.
- Young plant: Very small or recently rooted cuttings may need a full season of vegetative growth before they are mature enough to flower.
Address the day-length issue first, because it is the cause in the vast majority of cases. A healthy, well-fed Mona Lavender that experiences natural autumn day lengths will flower reliably with no special effort.
Companion Planting and Design Uses
Mona Lavender’s purple flowers and dark foliage make it a natural companion for silver-leafed plants like dusty miller, lamb’s ear, and silver falls dichondra, which contrast beautifully with its deep purples and greens. It also looks striking alongside chartreuse foliage plants such as sweet potato vine or golden creeping Jenny, where the color tension creates visual energy in a shaded container arrangement.
In mixed containers, place Mona Lavender as the “thriller” or central upright element, with trailing plants cascading over the pot edge. Because it flowers during cooler months when many summer annuals are fading, it extends the season of interest in a patio display. Some gardeners grow it specifically as a fall and winter container centerpiece, bringing it out to replace spent warm-season plantings just as its flower spikes begin to emerge. The timing works out well in most temperate climates, making it a useful plant for anyone who wants color on a shaded porch during the darker months of the year.