Divide and conquer flagging perennials
Have your borders lost their bounce? Well now’s the time to split up congested clumps of f lowers 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.
Apart from giving tired perennials a new lease of life, dividing a large specimen into several portions means you’ll end up with surplus plants. These might have been given away in the past, but at a time of social distancing and when it’s hard to obtain plants elsewhere, use them to plug gaps in your own space.
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.
Of course, an overgrown clump is unsightly, tempering the aesthetic good looks of a bed, border or similar display. In some cases, the plant will have spread with abandon for many years to cover a large patch of ground, where weak, new growth surrounds a mass of dead roots and shoots in the centre.
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.
Dividing perennials is a crude, but effective method of propagation that anyone can carry out without the need for any specialist kit. All you need is a spade, 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.
There are several ways of physically dividing up clumps, with the method determined by the root system of the plant. For example, some plants have small, fibrous roots that come apart with little effort, while others form a tightly knit mass of fleshy roots that require a bit more oomph to cleave apart.
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 2in layer of organic matter, work it into the soil and rake level.
Aim to place very 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 12in to 18in 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, making sure the crown sits at the same level as before. Firm in place and water. Over the next few months, plants will need regular watering until established.