Propagating Hardy Perennials by Division: Whether or not we want to increase our stock of hardy perennials, there comes a time when we need to know how to propagate them. This is because most of them, sooner or later, become less attractive as they grow older, or need replacing as they exhaust the ground in which they are growing. Paeonies, for instance, will thrive in the same spot for years, but fibrous mat- rooted subjects like Michaelmas daisies, etc. should be split up every three or four years to keep them young and vigorous.
This division of old roots is the easiest of all propagating methods. In many cases it can be done either in spring or autumn, although some things such as scabious and catmint are fussy, and prefer to be moved just after they have started growing in the spring. An approximate rule is that spring flowerers are divided in the autumn and summer flowerers in the spring.
After carefully digging up the old plants, select vigorous young shoots with roots attached from around the outside for replanting. The old centre portion is generally worn out and not worth keeping.
If the idea is to rejuvenate a group of perennials and replant them in the same ground, it is a good idea to dig the old plants up in the autumn, and set them temporarily somewhere else. The ground can then be thoroughly dug and manure, removing any weeds, and the selected new pieces replanted in spring in the well-settled ground. The rooted pieces can be set singly or, to cover a larger area, in threes or fives a few inches apart, to be treated as one plant.
Where the purpose of propagation is to increase stock, shoots can often be taken off without disturbing the original plant and interfering with its growth and flowering. Use an old knife or trowel to sever rooted pieces carefully, and put these in pots to be kept and grown on until they are needed, perhaps the following year.
To raise new plants from subjects that are difficult or impossible to divide, shoots can be taken off as bare cuttings in spring and summer, and put in to make an entirely new root system. They do this best in a closed humid atmosphere under glass; setting them in pots or boxes in a closed cold frame is ideal. A cloche can be used if the ends are closed up, or a single cutting can be rooted under a jam jar in the open ground.
Where cuttings are particularly plentiful, as, for instance, with pinks, it is even worth trying some in the open ground without covering. Choose a moist, shady spot, and set them in an inch or so deep in a V- trench lined with a half-peat, half-sand mixture.
