In order to keep your stock levels healthy collect seed, take cuttings, layer or divide. The exact time to propagate varies according to species but now is ideal for many favourites.
The simplest approach is to take and store seed. Some plants, such as aquilegias, spread their seed throughout a border, so all you have to do is weed out the ones you don't want next spring. Other species, like hellebores, germinate immediately from green seed, so you'll find new seedlings emerging close to the parent plant. Dig them up and move them to a new home.
Ordinarily you need to collect then store seed over winter, but you may find the seed hasn't ripened properly because of the cool, wet, sunless summer. If you are collecting poppy seed, nip off the seed heads when they start to brown, but before they develop holes for releasing the seed. Collect the seed by turning the heads upside down in a paper bag and then store it in a cool, dry place, such as a drawer.
Treat nigella in the same way, but be more cautious with Sweet Williams or Cerinthe Major. I often don't bother removing the bits of dried husk, but because this summer has encouraged every fungus known to man, the seed cases may be carrying destructive fusts, so carefully winnow out this chaff.
A useful alternative to saving seed with many plants – among them fuchsias and tender species – is to take cuttings. Solanum romps up sunny south-facing walls before dying back in winter. In all but the most sheltered gardens, it won't grow again, so cuttings are essential. I find honeysuckle irresistible and this is a good time to increase my stock. I also take cuttings from dianthus because I insist on having lots of these wonderfully scented specimens but some need more greenhouse space over winter than I can spare.
Select clean, healthy stems that are free of pest or disease damage. There are two ways to take cuttings: stem cuttings and slips. For the former, use a sharp knife, scissors or secateurs. Cut a non-flowering stem just below a leaf node where there is a concentration of hormones which encourage root growth. Some plants, like perennial dianthus, produce side shoots, or slips. Gently tease them from the main stems, choosing stubby side shoots no longer than 6-7cm.
The general approach with cuttings is as follows. Prepare the cutting by nipping out the top of the stem and removing the leaves in its lower half with a very sharp knife to avoid damaging the stem. The growing medium should be moist but very free-draining and low in nutrient, being half compost or soil and half sharp sand or perlite. Take your cuttings and insert the lower halves into the pot, spacing them 2cm apart round the edge of the pot. Place the pot in a clear plastic bag with twigs round the edge to keep the plastic away from the cuttings. Blow into the bag, seal it with a plant tie and place the pot in a shady, warm place.
Most cuttings strike within a month and can then be moved on. First give each cutting a gentle tug – resistance means it has rooted. Give the pot a good soak, tip out the contents and gently tease out the seedlings. Pot each plant in a 5cm pot filled with a general-purpose compost and top off with a layer of grit.
Many plants can be propagated by layering, a traditional technique that's not used often enough. Prime candidates are border carnations. Choose a long shoot, bare at the base but with a healthy growing point. Remove all the leaves except the five pairs nearest the tip. Prepare the second leaf node below these for rooting. With a sharp-pointed knife, make a slit along the stem to each side of the node, making the slit 1cm long. Lighten the soil by mixing in sharp sand and cover the bare parts of the shoot with fine soil, pegging down with a U-shaped twig or peg. Water well.
The stem should strike within four to six weeks. Cut the umbilical cord with the mother plant and leave for a week or so to settle down. Transplant to a 5cm pot with a 50:50 mix of general-purpose compost and sharp sand.
With a bit of patience, you'll find layering works well with many herbs like thyme, rosemary and lavender, plants that produce low, pendulous branches and readily strike themselves. Use the same technique to get more currant and gooseberry bushes. n