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Dividing and Transplanting Perennials

Perennials grow and expand in various ways and at different speeds. The rate and type of spread depends on the nature of the plant, the location and the growing season. Some perennials will form a large clump more quickly than the surrounding plants and have an almost invasive nature. Others will stay quite confined year after year.

Whichever types you have, most will need to be divided every 3-4 years. Similarly, tulips and daffodils need to be dug up and divided or they will become overcrowded and cease to flower. Aggressively spreading perennials need to be divided to ensure that your garden does not become overcrowded with one plant.

Not all plants are divisible. Hollyhocks, Columbines and Delphiniums are examples of perennials which resist division and are best expanded from seed. Others, such as Lavender, Sage or Wormwood, are best propagated by cuttings.

Candidates for division are usually fairly obvious. Monarda, Lamb's Ears, Evening Primrose, Creeping Phlox or other creepers all spread by underground plant parts and readily expand into the soil around them. The perennials themselves will be rejuvenated and you and your gardening friends will benefit from this new, abundant supply of plants.

The best time to make most divisions is in late August or early September when the plants are dormant. As the fall approaches, the plants will come out of their summer dormancy and form new roots in time to be established before the winter. There are exceptions to every rule, so if you are unsure whether the plant you wish to divide or transplant should be touched now, in the spring or not at all, check with the experts at your local garden centre.

Spring and summer flowering perennials may be safely divided now. Those which flower from mid-August onwards are best divided in the spring. With invasive-type perennials such as Jerusalem Artichoke, Goutweed or Ajuga, the rules of division are much looser. I tend to tear these up on a regular basis to allow other plants to spread. Do your friends a favour when you give them as a gift and warn them not to plant these perennials in the midst of other favourite plants.

The first step is to trim the plants to about 6 inches (15cm) above the ground and water well prior to digging. After a few hours or the next day, when the water has sunk in, dig up the entire clump using a good quality garden fork and shake off excessive earth. When you look closely at the clump, you will notice that separate crowns have formed around the outside of the clump and these can often be easily torn apart. Perennials will usually die from the centre so it is these outer portions which are used to replant. Some plants will untangle themselves readily, while others will be woven together tightly and require a more aggressive approach. You can try to pry the roots apart with your hands or you may use a sharp tool and slice through the clump to make several clumps about 6 inches in diameter. Select only as many divisions as you need for your own garden, pot some up for gifts and compost the rest.

Replant divisions in locations which you have previously prepared. The soil should ideally be rich in humus and free of perennial weeds. Plant firmly in the ground to eliminate air spaces and be sure to plant at the same, original depth. Water the transplants immediately using a dilute solution of 10-52-10 water soluble fertilizer. The high phosphorous fertilizer plus a rich humusy soil will encourage rapid root growth so that the plants are well established prior to freeze up. You can also use a high phosphorous granular fertilizer such as 8-12-6 or bonemeal and mix this into the soil prior planting. Mulching the new plants will keep the soil warm for a longer period and permit greater root development this fall.

Daisy Moore, 1998.




Other autumn garden tips:

(click on the tip you want to read)


Fall Perennials
Planning New Beds for Fall Planting
The Garden in Transition
Dividing and Transplanting Perennials
The Dos and Don'ts of Staking Trees
Re-Seeding or Sodding the Lawn
Bulbs: Always Worth the Effort
Fertilizing the Lawn in Late Summer or Early Fall
Preparing the Vegetable Garden for Next Year
Growing Garlic ...For Food or Ornament
Priorities for Fall Gardening
Preparing the Garden for Winter





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Daisy Moore 2006