Dividing and Transplanting

Dividing and Transplanting

Dividing, transplanting and reducing the size of overgrown perennial clumps are essential tasks that rejuvenate the perennial garden resulting in healthier, better-looking plants and more perennials. You can expect clumps of perennials to need thinning or dividing and transplanting every three to five years. Some transplanted perennials can take awhile to get re-established and to bloom again.

Perennial clumps that have taken on a doughnut shape need to be divided and transplanted. This growth pattern where most of the vigorous shoots are on the outer perimeter with little growth in the clump’s interior is seen with dianthius, bearded iris, monarda (bee balm), phlox and lamb’s ears. Other perennials need to be divided because they have lost their vigour producing smaller flowers and fewer leaves. Other perennial clumps get congested in their centre, have grown overly tall, spindly or floppy.

Spring versus Fall:

Rule of thumb is to divide and transplant fall-flowering perennials in the spring and spring-flowering perennials in the fall. Spring-flowering perennials can be divided right after they have flowered so they have time to re-establish. Late summer or early fall when plants are still actively growing is an excellent time to divide most perennials.  Allow 30 days before the first hard frost so newly divided and transplanted perennials have an opportunity to send new roots into still-warm soil.  This is especially important in areas with early frosts, harsh winters and unreliable snow cover.

dividing and transplantingThere are exceptions. Perennials with fleshy storage roots should only be divided in the fall regardless of when they bloom.  These plants expend a lot of energy in the spring and need the summer to build up their reserves. These perennials are peonies, oriental poppies, astilbes, bearded irises, and Siberian irises.

Invasive perennials such as goutweed, snow-on-the-mountain, ajuga (bugleweed), campanula(bellflowers), lily of the valley, monarda(bee balm) and obedient plant need to be divided and thinned out regularly to keep them under control every year.

Some perennials should be left and not divided and transplanted such as gas plant (dictamnus) and false lupine (thermopsis). Perennials with extensive, deep, brittle, delicate or tuberous root systems make dividing and transplanting tricky. These include butterfly weed, bugbane, baby’s breath, balloon flower and bleeding heart.

A number of perennials and biennials produce seedlings or plantlets making it unnecessary to move the parent plant.  These include hollyhocks, columbines, delphiniums, foxgloves and mulleins.

Contact Harmony Gardens Landscaping for flowerbed maintenance including dividing and transplanting your perennials.

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