Divide and conquer
Have your borders lost their bounce? Well now’s the time to split up congested clumps of flowers and give them a new lease of life
For keen gardeners, spring is the traditional time to rejuvenate congested clumps of perennials using a quick, easy and reliable technique. Known among old hands as division, plants are dug up while dormant, or just waking up, and split into smaller pieces – a portion of the original then takes its place in the ground.
Generally, perennials need dividing every three to five years, depending on their vigour. If left to their own devices, they can engulf other plants, outgrow their allotted spot or turn into mounds that are reluctant to flower. Dividing also keeps them healthy, strong and in top shape to fight off pests and diseases.
As a rule of thumb, perennials that flower after midsummer’s day are suitable for dividing in spring, while those that bloom before this date are best left until autumn. However, many prefer to divide everything in spring, as excessively wet or cold weather later in the year can result in sections rotting.
Among the long list of varieties that will benefit from being divided in spring are alstroemeria, aster, bergenia (elephant’s ear), heucheras, hosta, hylotelephium (herbaceous sedums), kniphofia (red hot pokers) and rudbeckia. The likes of astilbe, epimedium and helenium are best left until autumn.
A word of warning: not all perennials can be divided. Those with multiple stems that emanate from the crown of the plant or that produce a long tap-root are no-nos. This includes aconitum, gypsophila, lamprocapnos and lupin, along with ornamental thistles, such as cirsuim, echinops and eryngium.
All you need is a spade, a couple of forks, secateurs and a sturdy old bread knife. A wheelbarrow is useful for moving gear around and holding plants steady as they are being divided.
To divide achilleas, asters and other plants with a network of fibrous roots, lift the clump from the ground and plunge two forks into the centre, back-to-back. Split in two by pushing the forks outwards. Plants with looser roots, such as heucheras and hostas, are usually easy enough to tease apart by hand.
Perennials with sturdier roots need a bit more elbow grease. Place clumps of day lilies, kniphofia and delphiniums inside a wheelbarrow and slice up the rootball with a spade or carve into smaller pieces with a bread knife. Ideally, each chunk should have three to five healthy shoots and plenty of roots.
Prior to replanting a section of a divided clump in the same spot, dig in a little garden compost or leafmould. Those with enough free plants to create a new display should fork over the entire site, removing weeds and large stones. Cover the surface with a 5cm layer of organic matter, work it into the soil and rake level.
Aim to place tall perennials at the back of displays, graduating in height as you work forwards, with carpeting types at the very front. The spacing depends on the plant’s maximum spread. Most are happy set 30cm to 45cm apart but check online or in a plant encyclopedia for specific planting distances.
To plant, dig a hole that’s three times as wide as the divided section and the same depth. Place the plant in the centre and fill around the edges with soil, leaving the crown at the same level as before. Firm in place and water. Over the next few months, plants will need regular watering until established.