Lavender care: growing it in a pot and on a sunny sill

Light

Outdoors in summer, sunlight measures roughly 10,000 to 12,000 foot-candles, according to the University of Illinois Extension. Directly in front of a south window, the brightest spot in most homes, that drops to about 1,500. Lavender is a full-sun plant even by outdoor standards, so a sill gives it a fraction of what it evolved with. Expect thinner, paler stems indoors and few or no flower spikes. That is not a care mistake; it is physics.

To give it the best odds inside, choose an unobstructed south window, or west as a second choice, and turn the pot every few days so all sides get light. Penn State Extension suggests a backup for herbs that need full sun: two 40-watt cool white fluorescent tubes hung 6 to 12 inches above the foliage for 14 to 16 hours a day. Modern LED grow lights do the same job. As soon as nights warm in late spring, move the pot outside. Illinois Extension suggests easing houseplants into the outdoors over one to two weeks, a few more hours each day, before giving lavender the full exposure it craves.

Water

Water deeply and then wait. Push a finger or a wooden skewer into the pot: when the top half of the mix is dry, pour water slowly over the surface until it runs freely from the drainage holes, then tip out the saucer. A pot that never fully drains is the commonest way to lose lavender, because NC State links its root rot directly to overwatering.

Summer outdoors is the thirsty season. The RHS notes that container lavender dries out quickly because the roots have only a small volume of soil to search, and in hot spells it may need water once or twice a week. Clay pots dry faster than plastic, which suits this plant, but check them more often in heat waves.

Indoors in winter, flip the habit. Growth almost stops under weak light, the mix stays wet far longer, and cold wet roots rot. The RHS advises keeping container lavender fairly dry in winter, and that applies doubly on a windowsill. Give a small drink only when the pot feels light and the top few inches are dry. Slightly limp foliage in January recovers; rotted roots do not.

Soil and pH

Think gravel, not potting soil. NC State asks for perfectly drained soil on the dry side, and both NC State and Missouri Botanical Garden favor neutral to alkaline conditions with fairly low fertility. A peat-heavy houseplant mix holds too much water. Start with a loam-based or multipurpose mix, as the RHS suggests, and cut in a generous share of coarse grit or perlite so water drains straight through.

Use a container with large drainage holes; the RHS recommends 12 to 16 inches across for a mature plant. A layer of gravel on top, the inorganic mulch Illinois Extension recommends outdoors, keeps the crown dry and discourages fungal spots on the lower leaves.

Humidity

Low humidity is no problem for lavender. The opposite is. Missouri Botanical Garden blames humid summers for many failures, and Illinois Extension lists high humidity and poor air circulation among the causes of decline. Indoors, never group lavender tightly with tropical plants or set it on a pebble tray. A spot near a window that is opened on mild days, or a small fan on low, helps the leaves dry quickly.

Temperature

Inside, Penn State Extension recommends herb rooms run 65 to 70°F (18 to 21°C) by day and 55 to 60°F (13 to 16°C) at night, and notes that most herbs survive the mid to low 40s. Lavender fits that pattern well, and a cool, bright room is better than a warm, dim one because cool temperatures slow growth to match the poor winter light.

English lavender is the hardiest type, and the RHS says it can usually stay outdoors in winter if the soil drains freely. Roots in a pot are less insulated than roots in the ground, though, so a container plant is more vulnerable. If you overwinter outside, shelter the pot against a house wall out of the rain. Tender types such as Lavandula dentata must come in before frost.

Fertilizer

Lavender evolved in poor soil, and rich feeding makes it soft and floppy with less fragrance. The RHS says plants generally do not need feeding, and Missouri Botanical Garden prefers soil of low fertility. A pot does run out of nutrients eventually, so in spring and summer give a balanced houseplant fertilizer at the label rate at the long end of the University of Illinois Extension guideline of once every one to three months. Skip feeding entirely from fall through winter.

Work out the dose for your watering can with the fertilizer dilution calculator →

Repotting

Move lavender into fresh mix in spring as growth resumes, when roots show through the drainage holes or the pot dries out almost as soon as you water it. Penn State Extension sets the same trigger for potted herbs. Go up only a size or two at a time, because a big pot of wet mix around a small root ball is exactly what this plant cannot tolerate. Keep the plant at its original depth; burying the woody base invites rot.

• Roots push through the drainage holes
• The mix dries out within a day of a thorough watering in summer
• New shoots come in smaller than last year

Propagation

Cuttings are the reliable route. The RHS recommends softwood or semi-ripe cuttings from young shoots in early to midsummer, or hardwood cuttings taken in late fall from a fresh flush of growth. Strip the lower leaves from a nonflowering shoot, insert it in a gritty mix, and keep it bright but out of hot sun until roots form. Plants from cuttings match the parent exactly.

Seed is slow to germinate and, as Illinois Extension points out, many varieties do not come true, so seedlings of a named cultivar will vary.

Methods: Softwood or semi-ripe stem cuttings, Hardwood cuttings after flowering, Seed (variable for named cultivars) · Best season: early to midsummer for softwood cuttings; late fall for hardwood cuttings.

Common problems

Most lavender problems come back to water and light. A plant that wilts while the mix is wet has root rot; one that stretches toward the window with pale, widely spaced leaves is starving for sun. NC State and Missouri Botanical Garden both name leaf spot and root rot as the main diseases. Woody, bare stems are a pruning issue: the RHS advises trimming each year just after flowering, removing spent stalks and about an inch of leafy growth, but never cutting into old wood, which rarely sprouts again.

Not sure which one it is? Try the plant problem diagnosis tool →

Is the lavender toxic to cats and dogs?

The ASPCA lists lavender as toxic to cats, dogs and horses. Its toxic principles are linalool and linalyl acetate, the same aromatic compounds that give the plant its scent, and a pet that chews the plant may show nausea, vomiting and loss of appetite. NC State rates the severity as low and tags it as a problem for dogs, cats and horses. Keep potted lavender out of reach of a cat that likes to nibble, and call your veterinarian or the ASPCA Animal Poison Control Center at (888) 426-4435 if a pet eats a significant amount.

Check any other plant against the ASPCA lists →