Grow more plants the easy way

Filling a garden, however small, with plants can be a costly business but there is an easy way to grow plenty for free. Many of the permanent plants in your garden are going to be herbaceous perennials – ones that die down in the winter, but come back year after year. These are not only great value for money in the first place, but the majority of them will gradually ‘bulk up’ in just a few years to give you a large clump that can be lifted and split into new plants.

The process of division after such plants have spent 3-4 years in the ground makes good sense for your pocket, as well as benefitting the plants themselves. Development of many herbaceous perennials involves trying to increase in size to out-compete neighbouring plants and is the simplest form of vegetative propagation. The centre of the plant will gradually become older and weaker as it uses up the nutrients in the soil or compost around its roots. Meanwhile, the edges of the clump will continue to produce new stems and roots, growing out in search of ‘pastures new’. It happens in nature and gardeners can take advantage of this to harvest outer sections of the original plant which are strong growing and healthy.

The best time to divide plants

Ideally herbaceous perennial plants are best lifted and divided either in the autumn or spring. As a rule, spring-flowering plants benefit from being lifted, split and replanted in the autumn. At this time the soil is still warm and the divisions can re-root and establish before they need to grow and flower immediately in the spring.

For summer-flowering plants, it is probably best to leave them in the autumn and instead lift, split and re-plant in spring just as they are starting into active growth. The main reason for not touching them in autumn is that they will benefit from have chance to gradually die down and toughen up in the soil overwinter so that their rootstock is packed with stored sugars for growth in spring. Disturbance in autumn can interrupt this essential process and breaking roots can cause them them to rot in the ground – particularly in a wet winter

How old does a plant need to be before it can be divided

Plants that grow quickly, such as rudbeckias, asters and some ornamental grasses will soon bulk up into a large clump can be lifted and split after just 2-3 years. Slower growing species, like astrantias, delphiniums and peonies are best lest for 4, 5 and 6 years respectively. And don’t let anyone tell you that shouldn’t disturb peonies: I’ve lifted and split 6-year-old clumps with no problem. Just try not to break too many of the fleshy roots.

And I’ve also divided astrantias every couple of years in spring just as they’re starting into growth to quickly make more plants to fill a re-vamped border in my back garden. Planning ahead for re-planting means that you can bulks up the numbers of a particularly species or variety so that you can plant in 3’s, 5’s or greater quantities to get more impact.

Lifting and dividing plants

I use a garden spade or border fork to lift the plants that I want to divide, carefully digging around about 10cm (4in.) away from the edge of the clump or main shoots. Take care to dig down vertically to the full deep of the spade or fork, all the way round the plant, before levering it out. This way to will reduce the chance of ripping or tearing the roots. Extra time and care spent doing this will really pay dividends.

With the clump out of the ground, carefully crumble off the excess earth, to expose the edges of the clump or root system. You’ll usually find more soil attached to the base of the rootball so take a little time to shake this off.

Depending on the type of root system that the plant makes, you’ll need to employ one of a few different methods to divide the plant. Species that make a loose, open network of roots may just fall apart in your hands as you crumble the soil apart. Others will have a dense, fibrous mass of roots that can be cut through with a spade or an old bread knife. A few plants make thick, fleshy roots which need to be carefully cut with a sharp knife to minimise damage.

Whichever way you end up splitting the clump, each division needs to be composed of a good section of roots with growth buds attached to it.

Ways to improve the soil for re-planting

It’s a good idea to improve the soil by adding well-rotted garden compost or bagged organic matter. Fork the immediate area deeply where you intend to plant and add a spadeful of compost or organic matter to surface, forking it in. Then dig out a planting hole, large enough to accommodate the roots of your division. Set it in place so that the growth buds are sitting very slightly below the soil surface and crumble soil into the hole around the roots, firming it in place with your fingers as you go.

Water the divisions well and watch them grow! Division is the perfect way to get make free plants and fill your garden with colour.