Once you have herbaceous perennial plants, it is quite a simple matter to increase them – either by division, layering, root cuttings, and stem cuttings.
Propagating herbaceous Perennials can be carried out in various ways - all of them quite easy.
If there is a problem with propagating your own perennials, it is simply that it is so easy to do, that you will probably end up with more young plants than you can use!
If this is the case, don't simply discard them, but seek out friends who need to be 'educated' about using perennials in their garden.
Herbaceous perennials are traditionally divided in the autumn. There are two reasons for this. Firstly, as perennials get older – after the first couple of years, they tend to send out new growth around the perimeter of the plant – thus leaving a ‘dead’ non-productive core in the centre.
If you lift and divide the plants in the autumn, you can discard the old woody centre of the plant and separate the rest into smaller sections which will grow as individual plants. It is quite possible to divide most perennials into 4-6 new plants after the first couple of years.
Some Herbaceous perennials can be increased by layering. To propagate in this way, you simply arch a stem down to the soil, and either pegging it down into the soil, or simply placing a stone over it. This is best done in early to mid summer. Depending upon the variety, the stem will root into the soil in a month or so. Cut it off in the autumn and treat it as a new plant.
Several herbaceous perennials can be propagated by taking root cuttings in the autumn or early winter. Oriental Poppies, Phlox, Bergenia, Bergamot, Solomon’s Seal, Day Lily etc can be increased this way.
Soft wood cuttings or semi ripe cuttings can also be taken in early to mid summer, and rooted in the normal way for cuttings! This is much easier and successful if you have a propagator, a cold frame or a greenhouse, but can also be carried out with the help of a clear plastic bag secured over the pot once the cuttings have been inserted Taking Cuttings.
Many herbaceous perennials can also be propagated by sowing seed. This is usually more successful if you buy your seed at a garden centre or specialist seed merchant – rather than ‘collect’ your own seed (Though seed collection is possible!) - See Seed Beds Here