How to Grow Rosemary (Indoors and Out)

Rosemary is the herb everyone buys and half of us kill — usually with kindness. A Mediterranean shrub built for sun-baked, stony hillsides, it wants more light and less water than almost anything else on the windowsill, and it sulks in exactly the warm, damp, dim conditions we think of as cosy. Get those two variables right and rosemary is close to indestructible: an evergreen, fragrant, bee-friendly shrub that can live for decades and hand you sprigs for roast potatoes all year. Here's how to grow it in the garden, in pots, and — with honesty about the difficulties — indoors.

Know the plant you're growing

Rosemary (now classified as Salvia rosmarinus, though you'll still see the old name Rosmarinus officinalis everywhere) is a woody evergreen shrub from the Mediterranean coast. That origin explains every care rule that follows: intense sun, sharp drainage, lean soil, dry summers, mild winters. Upright cultivars like 'Miss Jessopp's Upright' can reach 1.5 m and make a fine informal hedge; prostrate forms spill beautifully over walls and pot edges. The needle-like leaves are the giveaway of a drought-adapted plant — small surface area, resinous coating — and they're exactly why rosemary hates wet feet.

Light: the non-negotiable

Give rosemary the sunniest spot you own — at least six hours of direct sun a day, and more is better. Outdoors that means an open, south-facing position, ideally with a wall behind it to store warmth. Indoors, only a south-facing window truly qualifies, and even there winter light in northern latitudes is marginal; a small grow light running 10–12 hours a day turns indoor rosemary from a slow decline into an actual houseplant. A leggy, sparse, stretching rosemary is a rosemary asking for more light.

Water and soil: think stony hillside

• Drainage first: in the ground, work grit or sharp sand into heavy soil, or plant on a slight mound. In pots, use a container with drainage holes and a mix of roughly two-thirds multi-purpose or loam compost to one-third grit or perlite.
• Water deeply but rarely: let the top 3–5 cm of soil dry completely before watering again. Established plants in the ground often need no watering at all outside real droughts.
• Pots dry faster: container plants may need water weekly in high summer — but always check first. Winter watering indoors might be needed only every 2–3 weeks.
• Skip the rich diet: rosemary flavours best in lean soil. A single feed in spring, or a little fresh compost in the pot, is plenty; heavy fertilising produces soft, floppy, less aromatic growth.

Warning: overwatering is the number-one rosemary killer, and it's deceptive — a root-rotted rosemary wilts and browns exactly as if it were thirsty, tempting you to water it more. If the plant looks miserable and the soil is damp, the problem is water, not drought. Let it dry out and check the roots before reaching for the watering can.

Pruning and harvesting

Harvesting is pruning: snipping 5–10 cm sprig tips for the kitchen keeps the plant compact and branching, so cook from it often. For proper shaping, prune just after the main flowering flush in late spring or summer, trimming the whole plant back by up to a third. The one rule that matters: never cut back into old, bare, leafless wood — unlike lavender's cousin habit, rosemary rarely resprouts from it, and hard renovation usually ends the plant. Stop pruning about six weeks before your first frost so late soft growth isn't caught by cold.

Winter: the make-or-break season

• In the ground, most rosemary cultivars are hardy to about -10 to -12 °C (USDA zone 7); 'Arp' and 'Madeline Hill' tolerate a few degrees more. What kills them in marginal winters is usually cold combined with wet soil, not cold alone.
• In cold climates, grow rosemary in a pot and bring it in before hard frosts. The ideal winter berth is cool (5–13 °C) and very bright — an unheated porch, conservatory or cold greenhouse — not a hot living room.
• If it must winter in a heated room, give it the brightest window you have, a grow light if possible, and water sparingly. Dry indoor air is fine; soggy soil is not.

Tip: rosemary flowers in late winter and spring, in a season when pollinators find little else — an established plant humming with early bees is one of the quiet rewards of getting the overwintering right.

Propagation: free plants from cuttings

Rosemary roots readily from semi-ripe cuttings taken in late spring through late summer. Cut 8–10 cm of this year's growth — flexible tip, slightly firm base — strip the needles from the lower half, and stand the cuttings in water on a bright windowsill or push them into pots of gritty compost. Water-rooted cuttings show roots in three to six weeks; pot them up once roots reach a couple of centimetres. Rooting several at once is standard practice — expect a failure or two, and you'll still end up with backup plants for windowsill winters and gifts.

Common problems

• Powdery mildew (white dusty coating): the classic indoor and humid-summer complaint. Improve airflow, keep foliage dry, give more sun, and remove affected shoots.
• Root rot (browning plant in damp soil): unpot, trim mushy roots, repot in gritty fresh mix, and reform your watering habits.
• Dropping needles indoors: almost always too little light plus too much water — the winter double act. Move it brighter and cooler.
• Woody, bare base: the natural result of years without pruning. It can't be reversed by cutting into bare wood — take cuttings and start a successor instead.

Not sure whether that white film is mildew or the browning is rot? Snap a photo in the PlantMe app — its plant doctor recognises 500+ diseases and problems from a picture and gives you a treatment plan, so you're not guessing while your rosemary declines.