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Why divide?
Sometimes a plant may have outgrown its allotted space, overwhelming its neighbours and spoiling the balance of plants in a scheme.
 Many perennials become open as the growth in the centre ages and dies, these woody centres can be prone to disease and sap the energy of the plant, besides looking less than great. Bergenias, heucheras and clump-forming varieties of primulas are common examples of plants loosing vigour as they age.
Chiselling a piece off the side of a plant does it no good in the long term; gardeners who continually raid prized plants for such ‘slips’ can find it suddenly dies from exhaustion, all the new vigorous growth having been given away to friends in those ubiquitous newspaper parcels.
Dividing the plant revitalizes it, with the plus that it increases the number of plants enabling you to plant a bigger grouping, and the display of flowers and/or foliage is better than before. But remember that these new plants may take time to grow to full size, so don’t divide everything the eve before you host a wedding or grand event!
When To Divide
Divide autumn flowering plants in spring and spring flowering in autumn. The idea is to allow the maximum root growth to occur before the plant tries to flower, exhausting nutrient reserves that a skimpy root system cannot replace.
And mid-summer flowering plants? Many gardeners favour early spring, when plants start into growth. But autumn is fine as well if you are prepared to sacrifice the last blooms. In very mild climates you can play with these rules a little!
Conventional wisdom required division of perennials on a 3-year cycle; nowadays division is only undertaken when a planting scheme gets out of balance or the plant need rejuvenation. Some plants, such as paeonies, rarely need division and resent being messed with.
How to do it
Dig up the plant and divide it into small pieces. Sounds easy.
Before you start, check your tools; bugs and fungal spores from other plants that you may have been working with can be carried on your tools, so make sure that they are clean.
Dig up the plant, have a good look at it, as there may be obvious sections that it will divide into. Starting to divide with an idea of how many sections you are after is a big help. Each section should have good root systems, especially of thin fibrous feeder roots, and a minimum of two growth eyes or shoots.
Larger clumps of plants look more substantial and satisfying than itty-bitty scatterings; don't make divisions too small and re-plant in groups of three or more.
Some plants literally fall apart when you dig them up, others can be teased by hand, some require a hefty heave, and the very stubborn seem almost impossible to deal with single-handed. There are different techniques for all these plants
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Perennials age, and flowering reduces
Divide regularly to keep sedums dense, they obligingly separate by hand
Some Plants Needing Regular Division to Flower Well
Agapanthus
Anaphlais
Arthropodium cirratum Renga renga
Astilbe
Aubretia
Bergenia
Campanula persicifolia & others
Centurea
Delphinium
Dianthus Pinks
Echeveria
Euphorbia*
Francoa ramosa Bridal wreath
Geum
Helenium
Hemerocallis Day lily
Heuchera Coral Bells
Iris siberica Siberian Iris
Leucanthemum x superbum Shasta daisies
Monarda didyma Bergamot
Phlox paniculata
Rudbeckia
Saxifrage
Sedum |
Flower borders need work to maintain the planting balance
Larger clumps of plants look more substantial and satisfying | |
