Answers to your gardening questions December, 2006

How do I control bag worms?

Ron asks about those ugly bagworms that he found this fall on his arborvitae (large evergreens usually planted at the corner of a house foundation).

There are 20 species of bagworms in the US, but only 2 or 3 cause enough damage to plants to be of economic importance. The principal harm done by this insect is the destruction of foliage by the caterpillars. In Maryland and Virginia the bagworm can be found on arborvitae (Thuja), 14 types of Juniper, Eastern Red Cedar, Chinese Elm, Honey Locust and Eastern White Pine, Loblolly and Virginia Pines, Hemlock, Norway maple, Deodar Cedar and Spruce.

Small bags hanging from your trees are likely evidence of the bagworm.

The female caterpillar lives in a silken cocoon that resembles a bag, often with bits of leaves attached to the outside to disguise and strengthen the case.

She can produce 500-1000 eggs in a single mass, all within the bag.

She carries this bag as she feeds. A fully developed bag is about two inches long. Eggs are laid in Fall, and hatch in May or June of the following year.

During the Winter, handpick the bags from your trees and burn them.

Bacillus thuringiensis (Bt), a bacterial insecticide, is effective in controlling bagworms.

Also, there are several parasitic insects that are important in reducing numbers of bagworms. A sex pheromone has been identified that, when used in traps to lure the parasitic moth (Itoplectis conquisitor), has successfully interfered with the male moth's mating behavior, resulting in a nonpolluting and effective means of control. Unfertilized eggs of potential bagworms do not hatch.

Burpee sells a pheromone trap with bagworm bait. We suggest calling around (maybe Behnke's first) before trying a hardware store.

How can I prepare my shrubs for a construction project?

Another friend asks what to do for plants BEFORE starting a construction project. We strongly suggest you move the shrubs you value, if they are anywhere near the worksite, and if they are of a size that can be moved.

Construction workers are not conditioned to focus on where they put their feet, their ladders, the stacks of lumber, the pallet of bricks, etc. etc. Their focus is getting the construction work done properly and on time.

If you want someone to focus on saving your valuable shrubs, either move them yourself, or ask a professional to do it. Some of us have been known to put a sheet over a shrub too big to move, and tie up that shrub (gently) with strong string to lessen its girth. (Sometimes there is no visible damage when unwrapping occurs.)

Before you move a shrub, water it deeply three days before digging it, and then lightly the night before. Woody plants need to take up a lot of water through all their branches to help withstand transplant shock, not to mention the drying winds of Winter.

Water again after transplanting and then again two days later.

There is no faster way to lose a shrub than to leave it dry or very dry in Winter!

If the shrubs are wide, do not assume that the recent rains have supplied all the water they will need. With your hose/watering wand, reach under the branches and apply ample water to the root zone.

Going into Winter, most perennials are dormant and possibly not even visible (Hosta's are a good example). The plants themselves won't get trampled if near a jobsite, but the soil in which they are living may get so compacted by workers' feet that there is scant hope that the plants can push their way through that soil in Spring.

So, if you value your perennial beds (because you slaved over improving the soil), you may want to move all those perennials further away. Then, when construction is done, you can dig that soil (that may well resemble adobe brick), and amend it with leaf mulch about 12 inches deep.

The shrubs and the perennials that you move out of harm's way can be planted in temporary beds (or in the ground) made of topsoil/leaf mulch mix, and mulched very well. Plenty of watering, please.

Or, if you have plant pots (with holes in the bottom), put your perennials in them along with plenty of their soil, group the pots all together in a deep pile of mulch, being sure there is mulch atop each pot. Again, don't overlook watering!

If there is any part of your worksite where your soil will be disturbed, or excavated, it is 99% certain that the contractor will 'repair' that soil by bringing topsoil which will be mostly clay/gravel, or at the very least, soil that is devoid of any nutrients. Experience has shown that even if you request your contractor to bring decent topsoil at job's end, you probably will not get it.

So, please, do yourself a favor, and do not move your transplanted shrubs and/or perennials back into that pitiful soil. A plant is only as good as the soil it is growing in, and that includes grass-seed/ sod!

Amend, amend, amend your soil. Who knows, maybe the Universe will provide you with some warm days now and then to do all this important work.

What should I do before winter really sets in?

By far the best kind of winter protection for plants is mulch or some other healthy "blanket." If suitably blanketed, the ground freezes little or not at all. Plant roots and soil organisms remain partly active and can start functioning in the early spring when sunny, windy days, followed by nighttime frosts, have a drying effect on vegetation. Under these early-spring conditions, unmulched evergreens easily lose water through their leaves. Unable to replace moisture from the frozen soil, the plants often turn brown and die.

Mulching your perennial flowers, your shrubs and your trees is the last and the most important job of the year. It may make the difference between beautiful and healthy plants, and sickly, insect-ravaged ones.

Ideally, mulch should be applied after the ground has been frozen slightly. Realistically, though, our ground here does not even contemplate freezing until January or February. Who wants to go outside then to mulch?

In northern climes, snow is one of the best protective sinter mulches, but over a large part of the country snowfall cannot be depended upon to give continuous protection during the really cold months.

Most plants are protected if the ground around them is covered with a 3-4 inch layer of autumn leaves, especially dry oak leaves which are the least apt to pack into a tight layer. Easy Gardener is dedicated to raking nearly all leaves into the beds, thus protecting perennials and the root systems of shrubs/trees (otherwise known as "woodies").

Boughs of evergreens from your holiday decorations or late fall pruning provide an excellent protection for the smaller woody plants (dwarf evergreens, for example), or over perennials with an early rosette of leaves in the occasional warmth of February/March (such as daisies/Asters, Anemones, or peonies).    Any material which will not pack, such as salt hay, straw, excelsior, wood shavings, rock wool or mineral wool (we all have these items in the carport just waiting to go!   ha!!) may be used as a winter mulch.

If you are removing dead or dying foliage from your perennials and tropicals, pile all that up over the plants and put the tree leaves on top.  

Nothing is sadder than seeing Azalea beds raked/blown bare of all leaves, but with no mulch added to help the shrubs through winter.  

And, by the way, do not be in a hurry in the spring to remove all the mulch.    Mulches should be removed gradually and only when plants have begun to renew growth in Spring.      We gardeners are constitutionally unable to resist peeking at the soil in late Winter for signs of early Crocus.   Move the leaves aside, then put them back after satisfying yourself with the evidence that Spring is on its way!

See you in January 2007 when we are out checking on the Crocuses (Croci?)

Pat Howell is a Takoma Park gardener and landscape designer/contractor. She is available for hand-holding and answering questions through Deephaven Landscapers.

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