Growing Concerns 524: Storm damage, over crowded ground cover, siberian Iris

Early Summer!

Sharp, clean saw and time the best answers for storm damage to tree

Dear Janet,

In the heavy winds on July 4 our Norway maple lost a large limb. It snapped off close to the trunk and stripped about 2-3 feet of bark below the point where it snapped off. I'm not sure what to do to take care of it.


Dear M.

There is little that can be done to correct pruning when it goes badly, as it often does during a storm.

Prune to remove the stub but don't cut flush to the trunk -- leave any of the thickened base that didn't get torn away. That place where limb and trunk meet is called the branch bark collar. Arboricultural science has proven that the tree seals over pruning wounds most quickly and with least damage to the trunk if we preserve that collar in pruning.

Clean up the ragged edges of the tear in the bark. Paint and sealants are not necessary. They cannot protect the exposed wood any better than the tree itself can.

Watch the new growth over the next few years. You may have to do some pruning to thin out sucker growth, or might have to train new branches into pleasing positions by gently bending them while soft then tying them until they become woody. You might even have to make the tough decision to start over, if the tree doesn't make a strong comeback.


Dear Janet,

I have had a lush stand of Lily of the Valley for the last 15 years. It spread easily and was thick enough to choke out any weeds, planted along a fence row under some trees. This spring the center of the stand was randomly missing over half the plants. They just didn't come up, and some of the rest of them have crinkled leaves, partially brown leaves, or tips missing from leaves. What causes this? Is there any remedy for it?


Dear D.,

Perennials, including groundcovers such as lily of the valley, pachysandra and myrtle, become weaker as they get old and crowded. Winter cold may have damaged the crowns, just below the surface -- on lily of the valley these growing points are called "pips." This damage would be worst on the oldest, most crowded parts of the colony.

Once that damage is done, it can open the door for fungi such as crown rot that normally can't infect healthy tissue. These pathogens proliferate once the growing season starts and may spread. The most damaged pips probably died before sprouting while those with less damage may have weak growth such as you describe.

It's in the nature of a groundcover to become crowded. In the wild, this isn't a problem because the outer edges of the colony remain vigorous and keep spreading to new areas. As older parts decline, natural succession begins -- other species move in.

In the landscape, if we don't have unlimited space for groundcovers and don't want to play the fascinating game of planned succession, groundcovers should be rejuvenated occasionally. This means removing crowded parts and renewing the soil there so surrounding plants can fill back in. Imagine the groundcover area as a checkerboard. Use a sharp spade to remove and discard all the red squares, then backfill with compost and mulch.


Dear Janet,

I have a grouping of siberian irises on either side of my front walkway. What should I do once they have bloomed and the leaves/stalks flatten on the ground? Should I cut them back to the ground after blooming or gather the leaves and stalks, tie and wait until fall to cut back? Do they need to be thinned periodically?


Dear L.D.

Siberian iris will stand tall throughout the season if it's healthy, young and vigorously growing. You can deadhead or not, as you like -- I sometimes leave the flowering stalks to become seed pods for their winter interest. If your plants are flopping, it's time to assess the site and the plant's overall condition.

A site has to be right for plants to be healthy and vigorous. This species requires full sun and moist soil to reach its potential. Conditions on a site can change and you may have to compensate by switching species.

If the site is right but the plants have a declining or dead center, it's time to divide them. If a leaf from the center of the plant is smaller than one from the edge, or the center doesn't bloom as fully or with as large a flower as the edge, then it's in decline. This may happen every five years or so. Remove the old center, renew the soil and replant a lively young outer portion.


Green thumbs up

to the tenacity of well-sited, established perennial plants. They're bright spots after a bad winter, since they're most likely to survive tough times. They'll even wait patiently among a press of annual weeds while their wayward gardener takes until July to finish the spring weeding.


Green thumbs down

to planting a big tree right on a property line without the neighbor's informed consent. Check references for the tree's eventual size, then position or maintain it so that it remains within your jurisdiction, or be prepared to deal with problems such as "Hey, who cut my tree?!"

Originally published 7/12/03