Eight plants to propagate in late summer

Whether you’re gardening on a budget, have a new garden to fill or have favourite specimens that you’d like more of, plant propagation is a useful technique that means you can create new plants free and now is the ideal time to scour your borders and containers for suitable cutting material. In some cases the cuttings will root within weeks, others will take longer, but come next spring you’ll have a bevy of young plants raring to grow.
While there are a range of different propagation methods, September is a good time for semi-ripe cuttings, which refers to the growth on the plant that is suitable for propagating — the stems should be firm but with soft, pliable tips. These are halfway between soft-tip cuttings taken in spring and early summer when the new growth is still flexible and hardwood cuttings that are taken in winter when the whole stem is firm and not bendy.
Semi-ripe cuttings are useful for plants such as Mediterranean herbs that have a tendency to become woody as they age and less productive in terms of flowers and foliage. Take some cuttings now and by spring you’ll have vigorous new plants ready to replace the tired old ones. These cuttings are also a cost-effective way to create sufficient plants to make low hedges of lavender or rosemary. For borderline hardy and tender perennials it means you can ensure you have plants for next summer, and it’s much easier to look after a few pots of cuttings of tender plants than have to overwinter large mature plants, which can take up a lot of space.
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Some plants are easier to propagate than others, so always take plenty of cuttings, as this will increase your chances of success, and don’t get dispirited if your first attempts don’t come to anything. Even the most experienced gardeners have cuttings that fail to form roots.
I like to prepare my pots and compost first so I’m good to go once I have the cuttings. Use a John Innes No 1 seed and cuttings compost that will be free-draining and low in nutrients, providing the perfect rooting conditions.
Alternatively make a 50:50 mix of multipurpose compost with sharp horticultural sand. Plastic containers are fine, but the porosity of terracotta pots can help to encourage quicker root development. It’s also important to make sure your secateurs are really clean and sharp — you want to make cuts that don’t create snags and tears, and you don’t want to introduce diseases.
The perfect cutting material will be healthy and have growth that is typical to the rest of the plant, so avoid anything that looks sickly or that’s growing in an odd way. Ideally the stems you pick shouldn’t be ones that are flowering, but this can be easier said than done on floriferous plants such as salvias, so don’t worry if you can’t find non-flowering shoots.
Morning is the best time to take cuttings as plants are plump and full of water and the cuttings are therefore less likely to wilt. The cutting should be about 15cm long — remove the cutting above a leaf or set of leaves on the parent plant. Pop the cuttings into a plastic bag — those with a seal allow you to close the bag to prevent the cuttings from wilting. Once you’ve taken all the cuttings you need it’s important to pot them up as soon as possible.
The base of each cutting should be trimmed to just under the bottom leaf or set of leaves — this is where the plant has cells that can develop into roots — then the bottom leaves should be carefully removed to create clear stems, leaving behind four leaves. Snip out any flowers if necessary, then pinch out the growing tip. You can dip the base of each cutting into hormone rooting powder, which can help to stimulate root growth, but it isn’t essential.
Insert a plant label at the edge of the pot — this is where the drainage and air flow are best — and wiggle it in the compost to create a slit into which a cutting can be inserted. Repeat, spacing the cuttings out around the edge so that they are not touching. Water the compost, allow the pots to drain, then pop them somewhere under cover that’s bright but out of direct sunlight.
Some cuttings benefit from the pots being covered with clear plastic bags to create a moist atmosphere around them to reduce water loss, but remove the bags at least once a day for about half an hour or so to get rid of the condensation that will build up, otherwise fungal diseases can take hold. Plants with hairy or downy leaves are best left uncovered.
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Check the base of the pots for signs of roots — it could take a couple of weeks to several months before you see anything. Once you can see roots, tip out the cuttings and replant each one into their own pot — this time use a John Innes No 2 compost or multipurpose compost. Keep the young plants somewhere frost-free and bright over winter and water sparingly so that the compost is neither waterlogged nor bone dry.
Rosemary This evergreen Mediterranean herb loses its vigour as it ages, so cuttings will produce a batch of healthy young plants. Pull side-shoots downwards away from the main stems and they’ll come away with a sliver of the stem attached, which is known as a heel cutting. This bit of stem helps the cutting to root.
Agastache Hyssops produce a profusion of long-lasting flowers and are one of the best plants for attracting bees, but assuming they’ll survive the winter is risky — they definitely wouldn’t like the cold and wet in my garden. The good news is, they root easily from semi-ripe cuttings.
Pelargoniums These tender perennials can be moved on to a windowsill or into a porch for the winter months, but it’s still worth taking some cuttings. Short, fat stems root best, and leave them uncovered, as they’re prone to rotting in high humidity.
Verbena bonariensis This plant self-seeds all over the place for me but if it doesn’t do this for you, then you can take cuttings now, as you can with other verbenas such as V. hastata, V. rigida and the trailing ones in your containers and hanging baskets.
Penstemon These pretty perennials with trumpet-shaped flowers are not reliably hardy, so winter losses are common. However, cuttings taken now will provide an insurance policy if the parent plants succumb to the cold.
Salvias These are must-have plants for late season colour, but many of them are half-hardy or tender. If you have the space they can be overwintered in pots under cover, but taking semi-ripe cuttings is worth doing as they will readily form roots.
Lemon verbena The lemon sherbet-scented foliage of this herb from South America makes a delicious tea infusion. It needs winter protection, so take some cuttings now — the leaves will fall in late autumn, leaving bare twigs, but this is perfectly normal and in spring they’ll send out new shoots.
Heliotrope The marzipan-scented, purple blooms of this tender bedding plant are one of my favourites, but it isn’t always easy to find the taller varieties in garden centres, so if you do track them down, taking cuttings is the best way to ensure you have plants for next summer.