Plant Propagation – Tips for Dividing Plants
You have a plant you like, but have only the one, and would love to have more; you have several tender plants, and wish you knew how to take in case of a hard winter; you know of a rare plant, but the only way to obtain it is to grow it from seed; and what about that lovely Penstemon you saw in a friend’s garden — they cannot remember its name, so how can you possibly order it from a nursery!
Of course if you knew how to take a cutting, you could grow the Penstemon for yourself. Byand dividing herbaceous , you could fill all the empty spaces in with little strain on the pocket. But the best part of propagating your own plants is the feeling of immodest satisfaction in transforming a small, rootless piece of plant stem, or a seed no bigger than a speck of dust, into a mature flowering plant.
Herbaceous perennial plants are divided for two reasons: one is that you would like a generous group (so much better for making an impact) instead of one lonely plant; the other is for the sake of the plant — manyquickly use up the foods in the surrounding soil, their roots form a close-knit mat and they deteriorate at the centre of the clump.
Arguments continue about whether autumn or spring is best for division. In most climates early autumn is an excellent time, thus allowing many weeks for the roots to settle in warm soil before winter sets in. By moving plants at this time, it is much easier to see for yourself their colour, height, leaf-shape and, much more difficult to gauge in spring when there is little of the plant above ground, their overall spread. But, if you suspect a plant is tender, leave it till spring;in particular are likely to die if moved in autumn. Remember that plants divided in spring will need regular watering.
The general run of herbaceous plants, such as Phlox, michaelmas daisies (novi-belgii) and Campanula should be divided into quite small pieces: as a rule of thumb, the faster the plant grows, the smaller the piece; and the poorer the soil, the smaller the piece and the better you should prepare the planting hole. An important feature plant, like a , might be moved in a larger section, to make more of an impact the following year. When dividing some plants, such as Bergenia and Heuchera, particularly if the clump is long-established, you will find some pieces with a woody stem (20cm/8in long), and no roots; if you plant these stems firmly, up to the leaf rosette, they will soon make roots. When the divisions, always fork in some well-rotted manure or compost, at a rate of roughly two bucketfuls per square metre, then sprinkle on bone-meal, a general , or both, and work this in with the fork.
When to divide
In the heyday of the, when there was plenty of labour, every three years or so all the plants would be lifted at once, the border would be dug and manured, and the divided plants replanted. Even in a smaller border this is a major undertaking. So every year, check over your plants, and decide which of them need division, and deal with them one at a time. Signs of being in need of division, apart from the centre of the plant becoming old and woody, are fewer and smaller flowers and an overall appearance of lack of vigour. On rich, retentive soil plants will continue to flourish for longer than on thin, well-drained soils. On poor soils michaelmas daisies, Phlox, Helenium, Astilbe, , Leucanthemum x superbum and all the general run of herbaceous plants will need dividing every three years, but you may have another year’s grace on better soil. Rather than plant a whole bed, it is better to re-do a small section, say 2-3m (6-10ft) square, at one time by lifting the plants, digging that part of the border, adding some organic matter and replanting. This enables you to replenish the soil and will give divisions of several different herbaceous plants at once a good chance to compete with established neighbouring plants.
Some plants — Hosta,, day (Hemerocallis), peonies (Paeonia), Kirengeshoma, oriental (Papaver orientale) and hellebores (Helleborus), for example — can remain in situ for many years. If you want another plant of any one of these, just cut off a segment without disturbing the parent plant. But hellebores and hostas eventually start to deteriorate. The best method of dealing with this is to dig up the plant in early spring — after flowering in the case of hellebores, but with hostas when the shoots are starting to form — and wash all the soil off the roots. Using a sharp knife, cut the plant into sections, making sure each piece has a shoot, and cut away completely the woody centres and massed old root. Hellebores establish well from small divisions.
Certain herbaceous plants — Baptisia, Gentiana lutea,, Gentiana asclepiadea, for example — should never be disturbed in any way, and must be propagated from seed.
Dividing a Plant
Dig up the plant you wish to divide with a fork and pull it into pieces with your fingers, or, if it is a solid mass of matted roots, place two garden forks back to back in the middle of the clump and prise the roots apart. With very woody roots you may have to chop them into pieces with a sharp spade. Large, fleshy roots, like those of a peony, should be handled gently, and if you have to cut them use a sharp knife. Smaller plants, such as primulas, can be easily divided with your hands into separate crowns.
Replanting the Divisions
Discard any old woody bits from the centre of the plant, spread out the sections on the soil surface, spacing them roughly 30cm (1ft) apart. (If the weather is warm, keep the divisions in a bucket of water or under a damp sack until the last minute.)
Replant the pieces at the same soil level at which the parent plant was growing. Even if it is raining, water well to settle the roots. Prick over the soil surface lightly with a fork. If you have to plant when the soil is very dry, fill up the planting hole with water first.