How and When to Prune Rosemary Without Killing It

Never cut back into bare wood

This is the one rule that matters. Rosemary has very few dormant buds in its old brown wood, so a branch cut back to a bare section usually just dies from the cut downward. Unlike many shrubs, it will not push new shoots from an old stump, and no amount of feeding or watering will change that.

Before every cut, look along the stem for green needles below the point you plan to cut. If there are needles between your cut and the main trunk, the branch will regrow from them. If the stem below is bare brown wood, move your cut higher. When in doubt, take less.

1. Find the lowest green growth Run your eye down the stem to the lowest point that still carries needles. That is your absolute limit. Cut just above it, not below.
2. Take a third at most Removing more than about a third of the plant's growth in one go leaves too little foliage to support recovery, and rosemary recovers slowly at the best of times.
3. Cut just above a leaf joint A cut immediately above a pair of needles heals quickly and the shoots come from that joint. A long stub between joints dies back and can carry rot down into good wood.
4. Use sharp, clean tools Blunt pruners crush the stem and leave a wound that does not seal. Wipe the blades between plants so you are not carrying disease from a mildewed bush into fresh cuts.

A branch that has gone entirely bare and brown will not recover. Cut it out completely at its base rather than leaving it, and let a neighboring branch fill the gap.

Prune in spring, and again lightly after flowering

The main prune belongs in spring, once the risk of hard frost has passed and new growth is starting. Cutting then gives the plant the whole season to close its wounds and put on replacement growth. A second, lighter tidy immediately after flowering keeps the shape without taking much away.

Do not prune in autumn or winter. Fresh cuts made going into cold weather do not seal, the soft growth they trigger is killed by the first frost, and the damage runs back into older wood. In a cold garden, leave even light shaping until spring.

Every harvest is a small prune. Cutting sprigs evenly from all round the bush, rather than repeatedly from the nearest side, keeps the shape balanced and often removes the need for a formal prune at all.

Pinch young plants to build a dense bush

The shape of a rosemary is set in its first two years. Pinching an inch off each growing tip in the first season forces the plant to branch at that point, and repeating it two or three times through the season turns a single thin stem into a full framework. It costs a little growth and saves years of correction.

The alternative is what most neglected plants become: three or four long stems with all the foliage at the ends and nothing but bare wood at the base. Because bare wood will not reshoot, that shape is effectively permanent.

1. First pinch when it is six inches tall Take the top inch (2 to 3 cm) off the leading shoot once the plant reaches about six inches (15 cm). Two or more shoots will break below the cut.
2. Repeat every six to eight weeks in the growing season Pinch the new tips as they extend, right through spring and summer. Each round roughly doubles the number of shoots.
3. Stop by late summer Pinching late in the season pushes soft growth that will not harden before the cold. Stop about two months before your first expected frost.
4. Use the pinchings The tips you remove are the youngest and most aromatic part of the plant. They are worth using in the kitchen or sticking as cuttings the same day.

Renovating a leggy old bush

An old rosemary that is bare and woody at the base with foliage only at the tips cannot be cut to the ground and started again. What you can do is reduce it in stages over two or three seasons, always cutting back only to a point where green needles remain, and letting it refurnish between rounds.

Work on a third of the branches each spring. Cut those back to their lowest green growth, leave the rest untouched, and wait a full season. If the cut branches respond with new shoots, repeat on the next third the following spring. If they do nothing, the plant has passed the point of recovery and is better replaced.

Before starting a renovation, take half a dozen cuttings from the healthiest shoots. If the old plant does not respond you will already have replacements a year into growth, which is far better than starting from nothing.

Keep a record of what you cut

Rosemary responds so slowly that you cannot judge a prune within the same season. Noting the date of each prune, which branches you cut, how far back you went and whether they reshot turns two or three years of guessing into a clear picture of how hard your particular plants can be cut.

The same record is what tells you when a bush is finished. A plant that reshot readily three years ago and produces nothing from the same treatment now is telling you its age, and that is the moment to root replacements rather than to prune harder.

1. Note the date and the weather A prune done just before a cold snap behaves very differently from the same cut in settled spring weather. Without the date, you will blame the cut rather than the timing.
2. Mark the branches you cut A loop of soft twine on each pruned branch makes it obvious next spring which cuts responded and which did not.
3. Photograph the whole bush each spring Shape changes too slowly to see. A picture from the same spot each year shows whether the plant is filling out or steadily going bare at the base.