You don't have to be a mathematical genius to work out that there's nothing more satisfying than increasing your stock of herbaceous perennials by the process of 'division'.

This is 'value for money' gardening at its best - in a nutshell, you dig up one of your old plants, split it, and replant the new sections, further apart or in a new place. Without spending a penny, you suddenly have 2, 3 or more new plants to fill up the garden or give to friends!

September onwards is a great time to divide many perennials, as long as flowering is over - those which flower in early autumn are best left until the spring.

Once flowering is finished, vigorous growth takes place - splitting them at this stage means that they are able to develop new roots quickly before the onset of winter.

The cooler, wetter weather as summer ends provides the young plants with ideal conditions, and it's also an opportunity to tidy up, take stock and try your old favourites in new combinations.

How to Divide & Multiply...step by step!

Dig up the plant to be divided. Take care not to damage the plantÕs rootball with your fork!

Shake off excess soil, and place the clump on a flat surface.

Decide on your chosen method of splitting:

You can insert 2 garden forks, back to back, tines together, and pull the handles inwards, which will force the clump apart. You can use and old large knife or sharp spade and cut the clump into pieces, ensuring that each new section has some roots and some shoots.

Some plants with fairly loose rootballs may be so easy to separate that you can tease the sections apart by hand.

If your plant has a bare, woody centre, discard this and reuse only the younger plant material around the edge.

Cut back the top leafy growth all over, to about 15 cm from the base. This prevents moisture loss from transpiration (release through the leaves) and allows the new plants to concentrate initially on developing a strong root system.

If you want to put them back in the same place, add some compost or manure to the soil to revitalise it, and then plant the new sections 30 cm apart, at the same depth as before. Spread the roots out in the planting hole, firm in well and water copiously.

It's better to wait until spring to divide plants with fleshy roots such as Hostas: it's easy then to see where to separate clumps with a knife because the new shoots are already present.

For perennials with thick gnarled 'rhizomes' (creeping, swollen underground stems) such as Irises or Bergenias, split the clump by hand, and then cut the old stems into sections, so that each section has one or more buds. Cut off half of the leaves, straight across - this stops them from being loosened by wind - and replant so that the top of the rhizome is above soil level.

In prolonged warm and dry weather, continue to water well.

Dividing clump-forming herbaceous perennials every 3 or 4 years isn't just a way of increasing the number of plants you have - these plants actually benefit from being split up and replanted!

Old, central sections can be discarded, and the new plants you create will respond by growing energetically. We've listed some perennials which respond well to division - choose from these and, with a little patience, you'll soon have a spectacular show without spending a fortune.

With the addition of one or two evergreen shrubs in the border for winter interest, and perhaps some spring bulbs, mixed borders including perennials give us maximum impact at a time when most of us want to be outside enjoying our gardens.

Don't forget to e-mail us if you need further advice - or to tell us how successful you are with division and multiplication in the garden!