Rosemary looks tough enough to survive anything: narrow evergreen leaves, woody stems and a scent that fills the air whenever you brush past it. But it has a particular weakness in many British gardens. Cold, wet soil can kill a rosemary plant that would otherwise cope perfectly well with summer dryness.
The secret to planting rosemary is finding a sunny position where water drains away. Once you have that, the actual planting is straightforward. A young plant from a garden centre or a rooted cutting will give you a useful herb much sooner than starting from seed.
Choose a plant suited to the space
Rosemary is now botanically named Salvia rosmarinus, though you'll still see Rosmarinus officinalis on labels. Upright varieties make useful compact shrubs. Trailing forms spill over container rims or low walls.
Check the plant's eventual height and width before buying several for a narrow herb planter. An upright rosemary can become a substantial woody plant; it isn't a soft annual herb that disappears at the end of summer.
Choose a specimen with firm green shoots and good root growth. Avoid plants with blackened bases, extensive brittle dieback or water sitting in the nursery pot. If the label includes a cultivar name, keep it for future reference.
Plant in spring where possible
Rosemary can sometimes be planted at other times, but spring is the most reliable choice in cooler UK gardens. The soil is beginning to warm and the shrub has a growing season to establish before winter.
Young plants raised inside need hardening off before they are placed permanently outdoors. Give them gradually longer spells in a sheltered spot, avoiding sudden frosts and harsh wind.
Don't plant into frozen or saturated soil. If you buy a small rosemary during a wet winter, keeping it sheltered in a draining container until spring may be much kinder than pushing it straight into heavy clay.
Give it full sun and good drainage
A bright, sunny border, gravel garden or raised bed is ideal. Rosemary comes from Mediterranean growing conditions and dislikes having its roots constantly wet.
Look at the ground after a spell of rain. If water lies where you intend to plant, that is a warning worth taking seriously. Mixing a handful of grit into one small hole will not fix a poorly draining bed surrounded by impermeable clay.
For heavy ground, consider a raised bed, a mound with genuinely improved drainage or a container. The best place for rosemary isn't necessarily the herb bed closest to the kitchen door if that position spends winter in shade and water.
How to plant rosemary in garden soil
Weed and loosen the planting area, making space well beyond the nursery pot. Dig a hole large enough to receive the rootball without forcing its roots into a tight coil.
Slide the plant from its pot, supporting the compost rather than pulling by the stem. If roots are tightly circling, ease them apart gently. Position the rosemary at the same depth as it grew in the pot, keeping the woody base above the soil.
Backfill with the existing prepared soil and firm lightly. Water thoroughly to settle the roots, then allow the ground to drain. The Royal Horticultural Society recommends leaving at least 45cm between rosemary plants to allow for growth and airflow.
Plant rosemary in a container
The RHS recommends a pot around 30cm wide and deep or larger for a permanent plant. Choose one with generous drainage holes and enough weight to remain upright as the shrub grows.
Use a suitable peat-free soil-based compost, incorporating horticultural grit where appropriate for drainage. Put a little compost in the bottom, set the rootball at its old level and fill around it without burying the crown.
A pot on a sunny patio is practical because you can move it out of prolonged winter rain. Don't allow the container to sit in a water-filled saucer. Drainage holes only help when water can actually escape.
Water during the first growing season
The idea that rosemary 'doesn't need watering' applies mainly to established plants in suitable ground. A newly planted shrub still needs moisture while its roots explore the surrounding soil.
Water during dry spells, then let the upper soil begin to dry before watering again. Check the root zone instead of sprinkling the leaves every evening. In a container, wind and sun can dry the compost surprisingly quickly.
Once established in the garden, rosemary often needs little extra water. A potted plant remains more dependent on you during warm weather. In winter, reduce watering and prioritise keeping the roots out of saturated compost.
Does rosemary need feeding?
Rosemary in ordinary ground generally doesn't need much feeding. Rich, wet soil can encourage soft growth rather than the compact, aromatic shrub you want.
Container-grown plants kept in the same compost for more than a year may benefit from a modest general-purpose feed in late spring or early summer. Follow the product instructions rather than applying a concentrated mixture.
If the leaves turn yellow, check watering and drainage before blaming a nutrient shortage. A plant sitting in cold, saturated compost may struggle to use available nutrients even if there are plenty in the pot.
Trim it without cutting into bare old wood
Harvest sprigs from young growth when needed for cooking. Regular light clipping keeps the plant shapely and encourages branching.
The RHS recommends trimming rosemary annually after flowering to prevent straggly, bare stems. Avoid cutting hard into old woody sections that have no leaves, because rosemary may not produce fresh shoots from them.
If you want more plants, softwood cuttings in late spring or summer, or semi-ripe cuttings later in the season, can produce copies of a healthy established rosemary.
Keep it alive through a British winter
Established rosemary is hardy across much of the UK, but prolonged freezing conditions can damage it, especially in exposed sites. Roots in a pot experience cold differently from roots in the ground.
Move containers closer to a sheltered wall during periods of severe cold or prolonged rain, keeping them in suitable light. Insulating the outside of a pot can reduce root exposure in a hard frost.
Do not wrap foliage in impermeable plastic and leave it sealed for weeks. Check weather protection regularly. In very wet gardens, drainage is often as important as frost resistance.
Troubleshooting a struggling rosemary
Browning shoots after a wet winter may indicate root damage. Check how damp the soil remains and whether the plant's base is soft. Adding more water or fertiliser won't resolve waterlogging.
A dry, wilting plant in a small summer pot may need a thorough watering followed by free drainage. The symptoms of too much and too little water can overlap, so inspecting the compost matters.
A rosemary that grows long, floppy stems with little scent may be short of sunlight or growing in excessively rich conditions. Give the next plant a brighter position and prune lightly each year rather than attempting to rescue a heavily woody shrub with drastic cutting.