If you've already got a healthy rosemary plant, you can make more without buying fresh plants. A cutting is simply a piece of stem encouraged to produce its own roots. Once established, it becomes a separate shrub with the same characteristics as the parent. Rosemary cuttings are useful for replacing an ageing plant, filling pots beside a kitchen door or giving a friend a favourite variety.
When to take rosemary cuttings
Late spring through summer is a practical period for taking cuttings from healthy, actively growing rosemary. Choose shoots that have matured a little but are not completely hard and woody. These are often called softwood or semi-ripe cuttings, depending on the stage of growth.
Avoid taking material from a plant suffering badly from drought, pests or disease. A stressed parent is less likely to supply sturdy shoots. Work in the morning when possible, before the sun has dried the foliage, and prepare your pots before cutting stems so they are not left wilting.
In a mild year you may get useful material later, but rooting becomes less reliable as light and temperatures decline. A sheltered propagation area makes conditions easier to control.
Choose a suitable stem
Look for a vigorous shoot around 8–12cm long with healthy narrow leaves. Prefer a non-flowering stem, because developing flowers draw resources away from root formation. If only flowering shoots are available, remove the flower head when preparing the cutting.
Use clean, sharp secateurs or snips. Make the cut just below a leaf joint where possible. Put several cuttings into a clean container or damp wrapping while you work, particularly on a warm day.
How to prepare a rosemary cutting
Strip the leaves from the bottom few centimetres of the stem, leaving a tuft of foliage near the top. Leaves buried in compost can decay, encouraging rot. Don't remove so much foliage that the cutting has no remaining leaves to support itself.
If the lower stem is woody, you can try a fresh cut into healthier material. Avoid crushing the stem by forcing blunt scissors through it. A clean cutting has less damaged tissue and a better chance of staying sound.
Rooting powder is optional. It may be useful for some woody plants, but many rosemary cuttings root successfully without it. If you use a product, follow its instructions and avoid dipping a wet cutting directly into the main container.
What compost should you use?
Choose a free-draining propagation mix, such as peat-free seed or cutting compost amended with suitable horticultural grit or perlite if necessary. The compost should hold a little moisture but not remain soggy.
Use small pots with drainage holes. Moisten the compost before planting so you do not have to pour a heavy stream of water around freshly inserted stems. Make a hole with a pencil or dibber and insert each cutting so that the bare lower section is below the surface.
Firm the mix gently around the stem. Several cuttings can share one pot if they have enough space for their foliage and can later be separated without severe root damage. Label the pot with the variety and date.
Where to keep rosemary cuttings
Place them somewhere bright but out of strong direct midday sun while they lack roots. A sheltered greenhouse bench, propagating area or bright indoor position may work. Excessive sun can dry out foliage faster than the cutting can replace lost moisture.
Warmth helps rooting, but a hot, sealed environment can encourage fungal problems. If you use a clear cover to raise humidity, provide ventilation and keep plastic from resting directly against the leaves. Don't leave the pot permanently dripping with condensation.
Rosemary naturally likes airy, relatively dry conditions as an established shrub, but a fresh cutting needs enough humidity to limit water loss. Aim for balance rather than treating it like a water plant.
How often should you water?
Check the compost with a finger. Keep it lightly moist while roots begin to form, letting excess water drain freely. Repeatedly flooding the pot can starve developing roots of oxygen and rot the base of the stem.
If foliage droops sharply, consider heat, low humidity and rootlessness as well as soil moisture. Adding water when the compost is already saturated is usually unhelpful. A little temporary shade may be more effective than another soaking.
As rooting progresses and new growth appears, gradually reduce any humidity cover and allow the young plants to adjust to ordinary conditions.
How long do rosemary cuttings take to root?
There is no single guaranteed timetable. Warmth, variety, cutting maturity and moisture all make a difference. Several weeks may pass before roots become substantial enough for transplanting.
Don't pull a cutting out every few days to see what's happening. That can tear off newly forming roots. Gentle resistance to a very light tug and signs of fresh growth can suggest progress, although neither proves a strong root system has developed.
Once roots begin showing near drainage holes or the pot holds together as a rooted clump, you can plan the next stage. If a cutting turns black and collapses at soil level, remove it promptly rather than leaving decaying material among healthy stems.
Potting on your rooted rosemary
Transfer a rooted cutting into its own pot of peat-free multipurpose compost with good drainage. Handle the small rootball carefully and set it at its previous growing depth. Water to settle the compost.
Keep young plants sheltered for a while instead of placing them immediately in freezing wind or scorching sun. As they develop, give them increasing light and the free-draining conditions adult rosemary requires.
Rosemary grows into a shrub, so eventually it needs more space than a tiny propagation pot. A sunny patio container can suit it well, provided winter rain does not leave the roots waterlogged.
When can new plants go outdoors?
A rooted cutting isn't the same as an established garden shrub. Young plants are more vulnerable to temperature extremes, wet compost and damaged roots. Keep tender new growth frost-free until it becomes sturdy and has been hardened off.
Spring is a good time to plant well-established rosemary into the garden once the soil warms. Choose a sunny spot with excellent drainage. On heavy wet clay, a large container or raised planting position may be safer.
Common problems with rosemary cuttings
The base turns black: Overwatering or poorly ventilated compost may be to blame. Start again with cleaner pots and a freer-draining mix.
Leaves dry and fall: The cutting may be losing water faster than it can take it up. Reduce harsh sunlight and maintain moderate humidity.
No new shoots after a few weeks: Rosemary can be slow. Avoid disturbing the stem; check whether it is still green and firm.
Cuttings root but then die: The transition into a larger pot, excess water or sudden outdoor exposure can stress young roots. Pot on gently and acclimatise gradually.
Only one cutting survives: That's still a success. Growing several candidates is sensible, not evidence the method has failed.
Caring for your new rosemary plant
Once your new plants are growing strongly, treat them like ordinary rosemary. Give them sunshine, avoid sitting pots in water and trim lightly after flowering to keep the growth compact. Old rosemary doesn't respond reliably to cutting deeply into bare woody stems, which is another good reason to have younger replacements ready.
Take a few culinary sprigs after the plants have developed enough growth to spare. A tiny cutting needs its leaves to establish; wait before making it supply Sunday lunch.
Source
Royal Horticultural Society: How to Grow Rosemary, including propagation advice.