Many perennial plants and bulbs spread and grow outwards from their original planting site, and these can then be divided up to thin out growth or provide new plant material. Perennial plants are those that live for numerous years and come to life in spring. Examples include sedums, geraniums, lavender and dianthus flowers.
When perennials are left undivided, they grow larger and eventually may start to die out or lose vigour in their centre, as well as becoming too large for their site. By dividing them in spring or autumn, their vigour is retained and new plant stock is created. Some spring flowering plants, like irises, are best left until after flowering in summer. Ideally perennials should be divided every three years.
Perennials have different growth forms, so a slightly different approach will be needed according to the type involved. Some retain a central ‘crown’, others produce ‘offsets’ (small plantlets), while others are tuberous in nature.
Bulbs also produce offsets, and groups of bulbs can be lifted and divided in a similar way. Again this is best done after flowering and when the foliage has died down for spring flowering bulbs.