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Dividing precious perennials over autumn will plug gaps, improve displays and – best of all – won’t cost you a penny
AUTUMN is the traditional time for gardeners to fill empty spaces in beds and borders by splashing out on a host of new perennials. But the rising cost of living makes it highly likely that a few gaps will remain this season. If you already have perennials in your garden, there’s a clever way of improving your displays that won’t cost you a penny. I’m referring to a long-established propagation technique known as division, where an established clump is dug up and split into several self-supporting pieces.
Providing each chunk of a divided perennial has three or more healthy shoots and lots of roots, they’ll establish readily in warm, moist soil before winter. Once spring arrives, the vigorous sections will burst into life as temperatures increase, producing shoots that will soon be topped with flowers.
As well as supplying free plants, division actually helps perennials perform better. After three to five years, many will have outgrown their allotted space or become congested and shy to flower. Others look unsightly as they stretch out, forming a ring of living growth with a dead patch in the centre.
Old gardening tomes suggest perennials that flower before Midsummer’s Day are best divided in autumn, while those that flower after this date should be left until spring. In fact, most can be divided at either time, as long as they aren’t in active growth and divided plants are given close attention.
There are a few no-nos. Don’t divide plants in full flower as they won’t have the energy to form new roots, and avoid splitting them in summer when the ground is hot and dry. Divided plants will struggle to establish in cold, wet soil, so it’s best not to attempt it in winter.
Also, be aware that not all perennials like to be divided. Cirsium, echinops, eryngium, onopordum and other ornamental thistles have long tap roots that can extend down a foot or more. It’s hard to dig up clumps intact, and if these living anchors are damaged, the plant will fail to re-establish.
Start the division process by loosening the soil around the crown of plants with a fork, then lift clumps carefully from the ground. Shake off soil, snip off dead leaves and place the plant on a plastic sheet to prevent things getting messy. Work quickly to prevent roots drying.
There are several methods of dividing perennials, depending on the root system of the plant. Heuchera, primula and others with loose roots are easy enough to pull apart by hand, while plants with a dense root system, such as hemerocallis and kniphofia, are best carved into pieces with an old bread knife.
Siberian iris, yarrow and perennials with a close network of fibrous roots will need a bit more brawn. The traditional way of dividing them is to stick two forks in the centre of the crown, back-to-back. Push the forks outwards at the same time and you’ll split the clump in two.
Before replanting a section of a divided clump in the same position, work in garden compost or well-rotted manure. Dig a hole three times as wide as the division and the same depth. Place the plant in the centre and back-fill with soil, making sure that the crown is at the same level as before. Firm in place and water. Finish off by spreading a 3in-deep ring of composted bark, garden compost or leafmould around your specimens.
Make sure the newly planted sections don’t dry out before they are established. Water regularly during dry or windy periods for the next few months, even over winter.