If you noticed some space in your borders this year, or some of your more established plants didn’t flower as well as they have done previously, autumn is one of the key seasons to propagate.
Division is among the easiest and most effective ways to increase your stock. It involves carefully digging up clumps of perennials, which have either outgrown their allotted space or are no longer performing well. You’ll need to prise the root ball apart to become smaller clumps, each with a healthy section of roots attached.
Some perennials are simpler to divide than others. Crocosmias, rudbeckias, heleniums and hardy geraniums are pretty easy. You need to cut off the flowering stems and dead leaves, then dig up the clump, keeping the root system intact and then pull the plant into pieces from the outside, where there is young growth, making sure you have a healthy section of roots attached. Replant the divided clumps in soil which has been enriched with compost and water in.
For larger clumps, you’ll need to push two garden forks back to back into the centre and prise clumps apart. Discard the centre sections and replant the more vigorous outer sections.
Perennials with tougher roots, like hostas and hellebores, may take a bit more effort. I have found myself slicing through sections with a sharp gardening knife to divide them effectively, but they still come back.
Other plants suitable for division include phlox, sedum, delphinium, campanula, aster and achillea.
Another way to boost your stock is by taking semi-ripe cuttings in early autumn using this year’s young shoots that have started to go woody at the base. Plants suitable for semi-ripe cuttings include many evergreen and deciduous shrubs, including lavender, box, hebe, berberis and potentilla. They may take longer to root than softwood cuttings, so you will need to be patient.
Select 10cm-long shoots from a non-flowering stem with a woody base and soft tip, cutting just below a leaf joint and removing the lower leaves from the bottom third of the shoot. Trim the base with a very sharp knife, leaving a small piece attached. Dip the tip into hormone rooting powder, then put six cuttings around the edge of a 12cm pot filled with 50% seed compost and 50% sharp sand or perlite, watering in well and leaving to drain.
Place the container of cuttings in a greenhouse, or cover the pots with a clear plastic bag and put them in a warm, light position out of direct sunlight, and keep the compost moist but not sodden. If the weather turns chilly, use a heated propagator in the greenhouse at night. Hopefully, cuttings should have rooted by the following spring.
Layering is another way to increase your stock and is an ideal method for propagating rhododendrons, azaleas and hybrid clematis. Essentially, it induces rooting from the parent plant without cutting the shoots off. Bend one of the branches down to the ground, remove the leaves around the tip of a healthy shoot and then cut a slit in the nearby stem without completely severing it.
Dig a hole near the plant at the point where the wounded shoot touches the ground, adding a little compost, push the shoot into the hole and peg the branch down with a hoop of wire or a forked stick before covering it with soil. The plant may take longer than a year to root, but when it does, you can detach and replant it.