How to Grow Rosemary: Drainage First, Water Almost Never

Almost every rosemary that dies in a garden dies of wet roots, and almost every one of those is watered again shortly before it goes, because the symptoms look like drought.

Greying foliage, drooping tips, browning from the inside out. It reads as thirst. It is usually the opposite.

Where it comes from, and why that matters

Rosemary grows wild on dry, stony, sun-baked Mediterranean hillsides, in thin soil, with rain in winter that drains away instantly through rock.

Every piece of advice below is an attempt to reproduce that in a garden that is probably wetter, richer and flatter.

• Sun: six hours minimum, more is better.
• Soil: free-draining, poor, slightly alkaline. It does not want improving.
• Water: almost none, once established.
• Feed: none.

Treating rosemary well is what kills it. Treating it meanly produces a dense, aromatic, long-lived shrub.

Drainage, before anything else

On heavy or clay soil, do one of these before planting:

• Dig in sharp grit or coarse sand generously — a third by volume is not excessive.
• Plant on a raised mound, six inches or so above the surrounding level.
• Use a raised bed, which solves it outright. See building one.
• Grow it in a pot, which gives complete control.

Then plant slightly high, so water runs away from the crown, and mulch with gravel or grit. An organic mulch holds damp against the stem, which is exactly the condition that rots it.

In a container

The right answer in cold or wet climates, and a good one anywhere.

• Terracotta, ideally — it breathes and dries the rootball out between waterings.
• Compost plus a third grit or perlite.
• Generous drainage holes, and never a saucer with water in it.
• Water when the top inch or two is genuinely dry — weekly at most in high summer, monthly or less in winter.
• Feed once in spring, lightly, or not at all.

Pruning: the one rule

Never cut into bare wood. Rosemary does not reliably produce new shoots from old leafless stems, so a hard cut into a woody branch usually leaves a permanent dead section.

So:

1. Prune after flowering, in late spring or early summer.
2. Take no more than about a third.
3. Cut only into stems that still carry green leaves.
4. Trim little and often from a young age rather than waiting for the plant to sprawl.

This is the same discipline as pruning lavender, and for the same botanical reason.

A rosemary that has already gone leggy and bare at the base cannot really be renovated. Take cuttings from it and start again — which is why the cuttings step is worth doing before you need it.

Overwintering

Established rosemary is hardy to roughly 15 to 20°F, and hardier varieties such as Arp and Hill Hardy go lower. But hardiness figures assume dry roots. The same plant in cold, waterlogged soil dies at temperatures it would shrug off in a gravelly bed.

So in a cold climate:

• Ground plants: a sunny sheltered spot, sharp drainage, gravel mulch. Fleece in an extreme snap.
• Container plants: move against a house wall or into an unheated greenhouse or porch, and above all keep them out of winter rain. Cold and dry is survivable; cold and sodden is not.

Harvesting and propagating

Harvest year round. Cut sprigs from the tips as needed — that doubles as the light trimming the plant wants. Flavour is strongest just before flowering.

Propagate from semi-ripe cuttings in early summer: 3 to 4 inches, lower leaves stripped, into a gritty mix, kept just moist. They root readily.

Do this every few years as a matter of routine. Rosemary becomes woody and sparse after four to six years, and a young replacement already growing is a far better position than a leggy plant you are trying to rescue.