Rosemary hedge care and pruning

Both rosemary and lavender are Mediterranean plants that have found a good home in the free-draining chalk and sandy soils of East Kent. They look somewhat similar from a distance, both have grey-green or silver-green aromatic foliage, both produce flowers that draw in bees, and both share the same fatal pruning mistake: cut into old bare wood and the plant dies back from that point. Everything else about them is different.

Rosemary vs lavender: the key differences

In practice, the main practical difference for an East Kent garden comes down to flowering season and height. If you want early bees from February and you need something slightly taller than a lavender can manage, rosemary is the right choice. If you want the summer flower colour and the lower, softer silhouette, lavender edges it. Both plants together, planted alternately, is a combination that works very well along a sunny path or terrace edge.

Pruning rosemary: the method

Cut back rosemary immediately after its main spring flowering flush, which in East Kent usually falls in April or May. Trim the plant by roughly one-third of the current year's growth, cutting just above a pair of leaves or a side-shoot. Bypass secateurs give a cleaner cut than shears for individual plants; for a long run of hedge, lightweight shears are faster and the finish is acceptable if the blades are sharp.

The rule shared with lavender: never cut into bare, leafless woody stems. Rosemary does not regenerate from old wood. Stay in the green every single time.

A second light trim in August is optional. It tidies growth and keeps the hedge compact going into winter. It should be very light, no more than the tips of the new season's growth, and always with leaves still present below the cut. Do not cut rosemary hard in autumn or winter.

Varieties suited to East Kent

Rosmarinus officinalis 'Miss Jessopp's Upright'

The standard choice for a formal hedge. Upright habit, to about 1 m, with pale blue flowers. Keeps its form well with annual trimming after flowering. Easy to find in any garden centre in Kent and very reliable.

Rosmarinus officinalis 'Tuscan Blue'

More vigorous than Miss Jessopp's and with broader, darker leaves. Bright blue flowers. Can reach 1.2 m in a good season. Best for a slightly taller screen or where you want a bold, bushy hedge rather than a tightly formal one.

Rosmarinus officinalis 'Sissinghurst Blue'

A lower-growing, more spreading habit than the upright cultivars. Good for a loose, informal edge rather than a formal clipped line. Flowers are a deep blue. The spreading habit means it does not need cutting quite as often to stay within bounds.

Rosmarinus officinalis (species)

The standard culinary rosemary is also a reasonable hedging plant. Less refined in habit than the named cultivars but very available, inexpensive and useful if you want to take cuttings from the hedge for the kitchen as well as cutting it for shape.

When rosemary is not the right choice

Rosemary is a poor choice in a shaded or north-facing position: it becomes thin, flowers poorly and is more susceptible to disease without good light and airflow. In an exposed coastal position on the seafront at Sandwich Bay or Pegwell Bay, rosemary can be caught by a hard frost or salt scorch in a bad winter. In those positions, a tougher salt-tolerant plant like griselinia or hebe is more reliable.

On heavy clay that sits wet over winter, rosemary roots rot as reliably as lavender does. If you cannot improve drainage, choose a different plant. In East Kent's chalk and sandy loam soils south and east of the A256, those problems rarely arise.

Video: rosemary hedge pruning guidance covering technique and timing. Watch on YouTube.

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