The technique of dividing plants involves digging up established plants and separating them into smaller sections to be replanted. Dividing perennials encourages new growth, prevents overcrowding, stimulates flowering and, above all, creates more plants. Dividing them also provides a good opportunity to improve the soil around existing perennials and remove any weeds that might be wrapped around the roots.
When to divide perennials
Plants that flower in late spring, summer or fall should be divided in early spring. Wait until the first signs of growth appear before dividing. Early-blooming perennials should be divided in fall. Exceptions to the rule are sedums, daylilies and hostas, which, in my experience, can be divided anytime. Fall is my preferred time of year to divide peonies.
How to divide and transfer perennials
The goal is to dig up the entire clump of the parent plant, lifting it out with most of its roots intact. Use a sharp spade, garden fork or garden knife to carefully divide the roots. In many cases, once you loosen the soil or wash it away from the root ball, natural divisions become clear, and some plants will even fall apart on their own.
A good rule of thumb to remember when dividing plants is that the optimal size of a division is about one-quarter the size of the original root ball. Pieces this size are big enough to re-establish themselves quickly and small enough to not require division again for a while.
When planting the newly divided plants, use fresh soil, plant them in holes at least as wide as the roots and water them frequently until established. Do not divide perennials during periods of drought or on extremely sunny or warm days. Ideally, perennials should be divided in the morning or on an overcast day when light rain is in the forecast.
Page 1 of 2 -- Find out how often you should divide perennials on page 2
How often should you divide perennials?
• Every one to three years for: Aster, Penstemon, Monarda, Dianthus, Oenothera, Delphinium, Tiarella, Phlox, Coreopsis and Achillea.
• Every three to five years for: Astilbe, Campanula, Gaillardia, Rudbeckia, Hemerocallis and Liatris.
• Every five to 10 years for: Hosta, Geranium, Alchemilla, Pulmonaria, Siberian iris and oxeye daisy.
The five best spring-blooming perennials
1. Dawson's White Brunnera (Brunnera macrophylla 'Dawson's White'): The woodland perennial has light blue flowers. Shade to part sun. Zones 2 to 9.
2. White trillium (Trillium grandiflorum): Ontario's provincial flower has white blooms in spring that mature to pink in summer. Full shade to part sun. Zones 2 to 9.
3. Lungwort (Pulmonaria 'Baby Blue'): Displays light blue flowers and colourful foliage all season. Full shade to part sun. Zones 3 to 9.
4. Bloodroot (Sanguinaria canadensis): The clump-forming plant has showy white daisy-like flowers. Part sun to full shade. Zones 3 to 9.
5. English primrose (Primula): Available in a range of colours. Full sun to part shade. Zones 3 to 9.
|This story was originally titled "The Great Divide" in the March 2012 issue. |
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