Andrea is a garden writer and horticulture extension agent. She is a formally educated ornamental horticulturalist, but has a personal passion deeply rooted in edible gardening.

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LAZY DAISIES AND TIRED TULIPS: Dead Heading and Dividing Perennials to Increase Vigor
by Andrea Dee    

Have you noticed your obedient plant rebelling into a doughnut shape with an empty hole in the middle? Has ‘Rozanne’ lost her vigor, with less and less flare each year? Are your spring tulips a carpet of green instead of red? Or maybe your friends are dying for a piece of your lungwort? While most flower gardens start out lush and colorful early in the season, late summer and fall often yield a less desirable look. Don’t be afraid to chop on your plants, you won’t hurt them. A little deadheading and dividing can go a long way in the perennial garden.  

Pruning Perennials
On average, perennials bloom three to four weeks, however when deadheaded some can bloom for several months. A plant’s physiological purpose for flowering is to make seed in an effort to reproduce immediately after blooming. As gardeners our interest is not always in seed production, but more in a bounty of blooms. Perennials can be manipulated to bloom most abundantly when deadheaded through the season and fertilized midsummer if necessary.  

Some flowers like daylily (Hemerocallis spp.), Iris, toad lily (Tricyrtis spp.) and others that flower atop a long stalk, have stems that can be removed all the way back to the crown after flowering. This practice will encourage new buds to flourish later and keep the foliage clean and orderly. Keep height in mind when planting these types of perennials in the garden. Often the foliar crown is much shorter than the flower stalk so you may want to plan your garden design so that another plant can fill the voided space after pruning. Tall perennial grasses like switchgrass (Panicum virgatum) and ‘Karl Foerster’ grass (Calamagrostis x acutiflora 'Karl Foerster') make nice backdrops to long flower stalk perennials with low-growing foliage.

Butterfly bush (Buddleia spp.), Shasta daisy (Leucanthemum x superbum), Salvia, bee balm (Monarda spp.), bleeding heart (Lamprocapnos spectabilis), Scabiosa, Geranium and a whole lot of popular perennials are naturally long blooming but with some extra deadheading can keep their show of flowers even longer. Simply pinch back dead blossoms to the first good set of healthy leaves and new buds will generate quickly.  

Some plants like Coreopsis have so many blooms to dead head it may be difficult with a pair of pruners, midseason hedging a few inches into the canopy is recommended to force out a second show of color. Wait until these perennials are almost done blooming and there are more seed heads than flower buds gracing the foliage canopy before hedging back.

Clematis can be one of the trickiest perennials in the garden to prune. For the most part seasonal pruning rules apply to clematis as well. Prune spring-blooming clematis immediately after the blooms decline all the way to the ground if necessary, this will allow plants the entire season to put on new growth and set buds for the following year. Prune summer- and fall-blooming clematis just after dormancy since they bloom on current year’s growth. If you desire long vines to drape an arbor for instance, prune back to a healthy leaf bud, or to 1 foot tall if rejuvenating completely. Prune clematis regularly and avoid pruning into very mature wood since it does not always respond well to pruning.

Tools for pruning perennials range from a simple hand to a sharper blade. Deadheading blooms can easily be done by pinching back blooms by hand, or pruning with a pair of scissors, “sheep” shear pruners, or needle-nosed pruners. Pruning of stems and foliage will likely require a pair of heavy-duty pair of bypass garden pruners.  

Dividing Perennials
When plants are three to five years old they often need rejuvenation and benefit from division. This is also a great time to expand your garden with all the new starts you will dig up!  

When choosing plants to divide remember, perennials that flower between early spring and mid-June are best divided in the fall, and perennials that flower after mid-June are best divided in the spring. However peonies, oriental poppies, and true lilies should infrequently be divided in the fall.

It is time to divide bee balm, Astilbe, blanket flower (Gaillardia x grandiflora), Chrysanthemum, garden phlox (Phlox paniculata) and Salvia when clumps start to die out in the middle. If your lily of the valley (Convallaria majalis), bleeding heart, daylily, yarrow (Achillea spp.) or iris become too woody, or start to show yellow leaves, it may be time to divide and replant them as well. Perennials like coneflower (Echinacea spp.), speedwell (Veronica spp.), Russian sage (Perovskia atriplicifolia) and black-eyed Susan (Rudbeckia spp.) can overrun a small garden, and should be divided also. Ornamental grasses can be divided in fall, but have so much aesthetic value even while dormant in the winter that most gardeners prefer to leave then until spring for pruning.

Once a plant shows an inch or two of green shoots, use a sharp spade to dig up a large clump for division. You can use an old kitchen knife, a perennial knife, or my favorite a Japanese soil knife called a Hori-Hori to separate vigorous shoots and root. Tough, woody roots from the middle are hard to establish and should be discarded to the compost pile. Replant offsets at the same depth they were originally growing. Water plants to be divided well a few days before digging and again at planting time, and continue to water regularly throughout the next few weeks to re-establish roots.  

Deadheading and Dividing Bulbs
Flowering bulbs too can benefit from division every three to five years, especially tulips. Daffodil (Narcissus spp.), Crocus, bluebell (Hyacinthoides non-scripta), grape hyacinth (Muscari spp.) and snow drop (Galanthus spp.) all have a naturalizing habit and do not necessarily need to be divided to thrive. Tulip, Dahlia and iris can be rejuvenated to increase bloom size and bounty every few years.  

Whether you plan to divide bulbs or not, deadhead blooms as they die back and leave waning foliage until completely brown. This is a true test of patience for any gardener, but it is important that the foliage continues to photosynthesize and store energy in the bulb for the subsequent season. Some gardeners ease their eyes and tidy their tulip and daffodil beds for summer during this several weeklong natural process by bending and tying browning foliage into bundles with string or a rubber band. If you do plan to divide bulbs dig bulbs after foliage declines and energy is stored. Always dig bulbs instead of pulling to minimize damage of both the bulb and root hairs. Harvest bulblets, which are usually attached to the mother bulb and re-plant. The original mother bulb can also be re-planted and will often be rejuvenated itself.  

Host a Garden Party
Spring and fall division mark an excellent time to host your family, neighbors and friends for a garden party. You will surely have plenty of young plants to share! 

 

A version of this article appeared in a previous print edition of State-by-State Gardening.
Photo credits: Daylily and rose photos courtesy of www.maydreamsgardens.com; hosta photo courtesy of www.gardening-guy.com.

 

Posted: 02/06/19   RSS | Print

 

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