Dividing Perennials

-By Lynsey Grosfield-

A perennial plant is a gift that keeps on giving in a variety of ways: firstly, it graces the garden with blossoms and foliage year after year, and secondly, it grows beyond the margins in which it was originally planted, often making copies of itself and forming a clonal patch.

While the lateral spread is often a welcome attribute in a garden where there is still bare soil to colonize, some gardeners prefer to keep perennials growing in a circumscribed area, either for aesthetic reasons, or to leave a place for less competitive plants to shine. A clump of daylilies, for example, can easily overshadow a low-growing and slow-spreading dianthus.

Additionally, plants that have are fitting too snugly in a landscape can essentially become like a root bound potted plant: lacking in nutrients and space to expand, a too-big perennial clump can look wilted, stunted, and spindly, or even stop flowering.

Taking divisions from established plants can help control the size of perennials, invigorate tired old stands of established plants, provide fodder for sharing and trading plants with other gardeners, and also save money in starting new plantings.

The best time to divide perennials varies from plant to plant, although as a general rule, spring and autumn are the best windows for accomplishing this garden task. Ideally, some perennials should be thinned out this way every two to three years.

During the high heat of summer when a plant is fully leafed out and preparing to flower, disturbing its growth can lead to wilt, delayed or absent flowers, loss of vigor, or even death. In winter, between snow cover and frozen ground, unearthing perennials are usually just impractical.

Ideally, divisions should be taken in cool or overcast weather, which allows the foliage (if any) and roots a gentler transition into their new home. Using clean equipment, lifting the plant, teasing or cutting apart the root ball, and taking only the healthy (mold- and rot-free) sections for transplant should result in successful new plantings. When re-planting, it is a good idea to reinvigorate the soil around the newly-smaller plant with compost or manure.

As a sort of paradoxical general rule, smaller chunks of roots, tubers, or corms replenish themselves faster, so taking divisions that have only 5-10 growing stems (or “eyes”)—or comprise less than 25% of the original plant clump—can result in a fuller-looking garden faster.

So be it spring, autumn, or even a cooler snap in summer, it’s a good time to have a look at older perennials, and check out whether or not they need a little more space to shine.

Photo by Bri Weldon

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