Regional Gardening Reports :: National Gardening Association

In the Garden:
New England
September, 2007
Regional Report

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Iris bloom best when divided every few years.

It's Time to Split

It's hard to face the reality that frost is just around the corner and the garden is performing its swan song. There are still carrots, beets, kale, lettuce, and peppers to harvest. And I'm still cutting bouquets, which I'm savoring all the more because showtime is almost over. But tomatoes are succumbing to blight, and I've given up on getting any eggplants. Sigh.

The only good thing about the downturn in the growing season is we have time to focus on next year's garden. Because if we start now, just think what we can accomplish! The soil will hold just the right amount of moisture and air because fall applications of organic matter will have worked their wonders by spring; weed growth will be checked by our furious fall weeding to remove those that are flowering and setting seed; and perennials will be flowering exuberantly because they were divided and rejuvenated this fall.

This weekend I'll be focusing on the latter task. It's long overdue. I tend to let clumps get way too large, and put up with diminished flowering for a year or two before it hits me that I can do something about it. Fall is a good time for dividing certain perennials because they have begun the slide towards dormancy and are less touchy about being cut apart. Here are some guidelines:

1. Choose a cloudy day, preferably before rain is predicted. This will reduce water loss due to evaporation.
2. Water the soil so the roots are well hydrated.
3. Cut back foliage to about 6 to 8 inches to reduce water loss and for easier handling.
4. Dig up the entire clump so you can divide it more easily.
5. Keep the divisions moist and in the shade until they are planted.
6. Replant in soil amended with organic matter at the same depth plants were previously growing.
7. Water regularly and spread winter mulch.

Evaluate whether any of these plants could use dividing in your garden:

Each peony division needs to have several growth buds or "eyes," so the best way to see these buds is to dig the plant and rinse the soil off the roots. Then you also can see where the roots separate most easily -- good places to cut the clump apart using a sharp knife. Set the divisions into amended soil so the eyes are between 1 and 2 inches deep. If set any deeper, the plant may not flower. Be sure to amend the soil in a circle at least twice the diameter of the division.

Bearded Iris
Unlike peonies, iris bloom better when the clumps are on the small side. They grow from rhizomes, and the best dividing method for this type of root system is to use a spade to cut the clump into pie-shaped wedges that contain one or two fans of leaves. Discard old rhizomes and any that are damaged or diseased. Replant so the rhizomes are just above soil level. After planting, keep the soil moist but not wet; bearded iris don't like soggy soil. Blackberry lilies and lily of the valley are divided in the same manner.

Daylilies, with their fleshy roots, are very tolerant of dividing and transplanting. You can cut into the clump anywhere with a spade to create smaller clumps; there are no eyes to worry about damaging. The hardest part is digging up the mammoth clumps that seem to develop overnight. Push a spade or a knife straight down through the foliage and roots to separate the sections.

Hostas have similar root systems and can be divided the same way, although they don't need this rejuvenation and are divided primarily to spread the wealth.

Garden phlox have spreading root sytems that are best pried apart with two garden forks pushed back to back into the center of the clump. Other plants with similar root systems include asters, bee balm, and lamb's ears.

Leave As Is
Some perennials resent transplanting, so who are we to force it upon them! Those that like to be left alone include baptisia (quite a tap root), columbines, delphiniums, foxgloves, hellebores, Japanese anemones, lavender, rosemary, and Russian sage. That said, I dug up a young baptisia one year and moved it to a new location. It died, or so I thought. The next year the plant grew abundantly, and so did a shoot that I had inadvertently left behind in the former location. I now have two wonderfully huge plants that aren't going anywhere.

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