Gardening 101: Dividing perennials

0011) Clumping perennials can get overcrowded and start to deteriorate over time. Some will stop holding their flowers up well, some can die out from the middle while others just look tired and messy. Some need digging and dividing relatively frequently to stay looking their best. This clump of pulmonaria (unromantically known as lungwort) probably started as a single crown two years ago but grows rapidly.
0022) Dig out the clump, shaking off the soil. If you are not sure what you are doing, hosing off the dirt can make it easier to see the structure of the root system which varies between different plants.
0033) Part the leaves to find the separate sections growing from the centre or crown of the plant. Some plants just pull apart. An old carving knife is helpful and a meat cleaver is good for larger clumps with tough crowns. You can use a spade but it is hard to get accurate cuts. The pulmonaria yielded at least 15 divisions, all of which would grow as separate plants if I wanted that many.
0044) Replant the strongest divisions into soil which is well dug and friable. If you are only lifting and dividing every 10 years or longer, this can be a major task as soils compact over time. If you are doing it more often, it is easy as the soil stays looser. Spread the roots evenly and cover to the same level it was earlier. We like to add compost mulch and then water thoroughly but gently. Removing some leaves reduces the stress on the plant.
0055) These three perennials also benefit from lifting and dividing every few years. From left to right: an aster which just pulls apart into separate sections, mondo grass (ophiopogon) which also pulls apart but sometimes needs the runners snipped, and polyanthus which usually needs to be cut through the crown to ensure that each piece has roots attached.
0066) This patch of stachys (lambs’ ears) was dug and divided three weeks ago and has already recovered well because it is in full growth. Timing is not critical in our mild climate but done in midsummer, care needs to be taken to avoid the roots drying out and plants will need thorough watering for the first week.

First published in the Waikato Times and reprinted here with their permission.

“A good soil, like good food, must not be either too fat, or heavy, or cold, or wet, or dry, or greasy, or hard, or gritty, or raw; it ought to be like bread, like gingerbread, like a cake, like leavened dough; it should crumble, but not break into lumps; under the spade it ought to crack, but not to squelch; it must not make slabs, or blocks, or honeycombs, or dumplings; but, when you turn it over with a full spade, it ought to breathe with pleasure and fall into a fine and puffy tilth. That is a tasty and edible soil, cultured and noble, deep and moist, permeable, breathing and soft – in short, a good soil is like good people, and as is well known there is nothing better in this vale of tears.”

Karel Capek, The Gardener’s Year (1929)

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