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Mickey Rathbun: Divide and transplant perennials in the fall

  • Lush landscaped garden with flowerbed and colorful plants Elena Elisseeva—Getty Images/iStockphoto

  • Gardening tools and flowers on the terrace in the garden Alexander Raths—Getty Images/iStockphoto


Thursday, September 07, 2017

September is a good time to divide and transplant spring and summer-blooming perennials. The heat of summer is behind us and we’re looking ahead to five or more weeks of moderate temperatures before a severe freeze. (That means four or more hours of temperatures consistently below 25 degrees.) Rainfall in autumn tends to be plentiful, helping new divisions and transplants settle in before the weather turns to winter.

It’s possible to move or divide plants even when they’re in bloom if you are extra careful, but it’s easier and less stressful for the plants to wait until their flowering season is over. Late summer and fall bloomers are best left until spring for dividing and transplanting.

All perennials have different timetables for optimum division. If you notice that a plant’s blooms are getting smaller or fewer every year, or that its new growth comes at the edges rather than the center, those are signs that the plant’s roots are overcrowded.

Some plants, such as Baptisia, resent being tampered with and are best left alone. Many gardening guides provide lists of perennials and how often they like to be divided. If you’re not sure your plants are in need, it’s a good idea to consult a source. Most plants like to be divided periodically and will thank you for it by flourishing over the next growing season.

Transplanting can be a matter of need or preference. A sun-loving plant may find itself in an area that’s gotten too shady. The plant may be failing to thrive but you’re not sure why. Or you may just want to mix things up by creating new combinations of size, color or texture. Would the white astilbe look better next to the pink bleeding heart? Have the delicate blooms of the lavender balloon flower gotten hidden behind a patch of bionic black-eyed Susans? Let your imagination have some room to play.

Here are some tips for successful transplanting.

First, the day before you dig the plant, cut its foliage to about 6 inches and water thoroughly so that it’s well-hydrated. Roots dry out very quickly once exposed to heat and air. The ground also will be easier to dig if it’s somewhat moist. If possible, work on a cloudy day, or at least avoid the brightest sun of the day.

Start by digging around the entire plant, 8 to 12 inches away from the crown. Dig deep enough so that you can lift the entire clump with its roots and attached soil from the hole. Then clear away as much soil as possible from the roots so that you can see them clearly. Roots at the center of a plant that’s been growing undisturbed for a long time tend to be thickened, woody and unproductive and should be discarded. With a sharp knife or spade cut through the crown to make divisions that have healthy roots. Gently pry apart the roots, being careful to save as many as possible.

Return the plant to its hole and place your newly created divisions in a place protected from sun and wind until you’re ready to plant them. Depending on how long they’ll be out of the ground, you might want to wet them down and wrap them in damp newspaper. If you can’t replant them the same day, be sure they remain moist and sheltered.

Prepare the new planting site by digging up the soil, adding compost and removing rocks and roots. Within that area, dig a hole that’s about one and a half times as large as the plant’s roots. Mound the soil in the center of the hole and spread the plant’s roots over and around it. Make sure the crown is at or just below the soil line. Replace the soil gently but firmly and water well.

Make sure to keep the transplants well-watered until the ground freezes. After a deep freeze sets in, spread about 3 inches of mulch over the plants, keeping it away from the crowns. Salt marsh hay, straw and chopped evergreen branches are good mulches.

If you find yourself with too many divisions and not enough space, give your extras to friends and neighbors. Chances are, you’ll end up exchanging your plants for some new and different ones. Free plants are always a blessing. If they don’t work out, you haven’t wasted any money on them.

2017 Massachusetts Garden Symposium

This year’s symposium, presented by the Massachusetts Master Gardeners’ Association, will focus on the theme “Inspiration for Next Year’s Garden.” It will take place at Westford Academy Performing Arts Center in Westford, Sept. 23 from 8:30 a.m. to 3:30 p.m.

This year’s speakers come from diverse backgrounds and have different fields of gardening concentration. Thomas Rainer, author of “Planting in a Post-Wild World,” will lecture on “The Garden of the Future: Reimagining the American Yard.” David L. Culp, vice-president of Sunny Borders Nursery will talk about “Perennials: The Best Plants of Yesterday, Today and Tomorrow.” Kathleen Gagan, peony expert and owner of “Peony’s Envy,” will talk about “Designing Gardens with Peonies.” Janet Macunovich, who runs the website GardenAtoZ.com, will talk about tackling autumn cleanup in the garden.

In addition to these lectures, there will be a silent auction, shopping and raffle prizes. The cost is $90, which includes morning refreshments and lunch. No reservations will be accepted after Sept. 16, no refunds will be given after Sept. 16, and walk-ins will not be admitted.

For more information and to register, go to: http://massmastergardeners.org/2017-gardening-symposium/

Berkshire Botanical Garden Harvest Festival

Berkshire Botanical Garden will be holding its 83rd annual Harvest Festival on Oct 7-8, 10 a.m. to 5 p.m. There will be entertainment, local foods, regional artisanal handcrafts, kids’ activities, a haunted house, plant sale, giant tag sale, including jewelry and clothing, and more.

BBG is also seeking volunteers to distribute signs and work the festival. Contributions of gently used items/clothing etc. are welcome. Call 320-4794 to donate.

Admission: Adults: $7, kids under 12: free.

Begonia and Gesneriad Show

This annual show, presented by the Buxton Branch of the American Begonia Society and the New England Gesneriad Society, will take place at Tower Hill Botanic Garden in Boylston Sept. 16 and 17. There will be examples of a huge variety of begonias and gesneriads sporting a range of color, leaf texture, and pattern in this judged show. Hours are Sept. 16, noon to 5 p.m. and Sept. 17, 10 a.m. to 4 p.m. There will be a lecture titled “Fancy-leaved begonias … so where are the flowers?” Sept. 16 at 3 p.m.

The show is free with admission to Tower Hill.

Mickey Rathbun can be reached at foxglover8@gmail.com.