Growing Rosemary in Pots on a Sunny Windowsill

Why Rosemary Earns Its Place on the Windowsill

Rosemary is a plant of sun-baked hillsides and thin, stony ground. It sulks in rich, boggy soil and shrugs off drought, which tells you almost everything you need to know about keeping it happy. A bright, south-facing windowsill is about as close as most of us get to a Mediterranean hillside, and a pot means you can move the plant when the seasons turn. Best of all, it puts the herb within arm's reach of the chopping board — no wet walk to the end of the garden when the lamb needs a last-minute scattering of needles.

Rosemary is also genuinely useful in a small kitchen garden. It is evergreen, so there is something to cut in January; it is shrubby enough to look handsome on its own; and it takes kindly to the restriction of a pot, provided the drainage is right.

Choosing the Right Pot and Compost

Start with drainage, because this is where most windowsill rosemary dies. Choose a terracotta or unglazed pot roughly 20–25cm across for a young plant, and always with a hole in the base. Unglazed clay breathes, wicking away surplus moisture from the sides, which suits rosemary far better than a glazed ceramic or plastic pot.

• Base layer: a few crocks or a 2cm layer of gravel over the drainage hole to stop compost washing through.
• Compost: mix two parts peat-free multi-purpose compost with one part horticultural grit. A loam-based John Innes No. 2 with a good handful of grit also works beautifully.
• Feed: very little — rosemary is a light feeder and rich compost encourages floppy, tasteless growth.
• Saucer: fine indoors, but empty it twenty minutes after watering. Never let the pot stand in water.

Plant so the top of the rootball sits just below the rim, firm gently, and water once to settle everything in. Avoid burying the stem, as rosemary bark rots quickly when it stays damp.

Watering: Less Often Than You Think

The single biggest mistake is kindness. Rosemary wants to dry out between waterings. Push a finger two or three centimetres into the compost; if it feels cool and clinging, wait. If it feels dry, water thoroughly until it runs from the base, then stop.

On a hot windowsill in July, that might mean every second or third day. In December, once a fortnight — perhaps less. Watch the plant rather than the calendar:

• Overwatered: lower needles yellow and drop, stems feel soft and dark at the base, compost smells sour.
• Underwatered: needles look dull and grey-green, tips crisp, leaves shed when you brush past.

If you suspect root rot, take the plant out, trim away any black, mushy roots, and repot into fresh gritty compost in a clean pot. Rosemary often recovers if you catch it early.

Light, Air and a Light Touch With Feed

Give rosemary at least six hours of direct sun a day. Turn the pot a quarter-turn each week so it grows evenly rather than leaning towards the glass. Keep it well away from radiators — dry, baking air is worse than cool air, and it encourages red spider mite.

Air movement matters more than most people realise. Rosemary evolved in breezy places and dislikes stagnant, humid conditions, which is what a sealed living room provides. A window cracked open for an hour a day makes a real difference, as does spacing the pot away from other plants.

Feed sparingly: a weak liquid seaweed or tomato feed every three to four weeks from March to August is plenty. Stop entirely over winter. Overfed rosemary grows fast and soft, with pale, watery flavour and a tendency to flop.

Harvesting for Roasts and Dressings

Snip the top 5–8cm of soft growth with scissors or a sharp knife, taking no more than a third of the plant at any one time. Regular cutting keeps rosemary bushy; leave it alone and it will stretch into a leggy, bare-stemmed shrub. Harvest in the morning, when the aromatic oils are at their strongest.

To strip the needles, hold the sprig at the top and run your thumb and forefinger backwards down the stem. A fork works just as well and saves your fingers. Woody stems are worth keeping — they make excellent skewers for lamb or chicken, and they flavour the meat from the inside.

• Roasts: tuck sprigs under lamb, chicken or a tray of halved potatoes with garlic and olive oil.
• Dressings: chop finely with lemon zest, sea salt and good oil for a sharp, herby spoon-over for tomatoes or white beans.
• Infusions: warm sprigs gently in olive oil, then cool and bottle for dipping bread.

Getting It Through the Winter

Cold is rarely the killer — wet, dark conditions are. Rosemary survives a surprising amount of frost if its roots are dry, but it hates sitting in cold, sodden compost in a dim room.

From October, cut watering right back and move the pot to the brightest spot you have. A cool, frost-free porch, garage windowsill or unheated conservatory suits it far better than a warm kitchen. Keep it clear of draughty window frames and away from radiators, and never mist it — humidity is the enemy.

Repot every two to three years in spring, moving up just one pot size, and give the plant a light tidy-up after flowering to remove congested or crossing stems. Check the undersides of leaves for aphids, mealybug and whitefly, which thrive indoors in winter. A firm wipe with a damp cloth usually deals with a small infestation before it spreads.

Do those few things and a single pot will keep you in rosemary for years — through Sunday roasts, summer dressings and the grey weeks in between.