The Carlisle Mosquito Online

Friday, February 1, 2008


Oh, deer — they're eating our shrubs

Deer behavior is very erratic across town this winter — which just might explain why a

A deer feasts on a juniper bush on Ember Lane, where large numbers of deer have found the menu tasty.

mountain laurel or azalea on one property is left alone while another down the street is stripped clean. Some plants such as holly, crabapple and rhododendron are high on the deer's list and others, such as juniper and white pine, are quite low, but really hungry deer will eat anything.

Deer seem to target plants that otherwise have few pests and diseases, a frustrating habit. An arborvitae might be easy to care for, and would present a serious problem only if it were completely devoured down to its stubs.

Most deer-eaten plants in Carlisle can sustain some damage and will rebound in the spring, but survival and beauty are two different things. Evergreens store most of their energy in their foliage, and plants such as crabapple start moving a lot of high-energy sugars to their dormant buds in late winter. Browsing deer rob a plant of the energy it needs for both growth and defense. When spring arrives, the plant will be challenged by any number of insects and fungal diseases.

Even if your shrubs are severely damaged this winter, starting a combination of the strategies listed below will encourage the deer to change their habits and give your landscape an opportunity to thrive. Protected from deer and with some TLC, many severely browsed shrubs will be presentable again in a season or two.

The lower branches of these PJM rhododendrons, also on Ember Lane, have been stripped by the deer. Notice how close to the house the deer have come.

It would be wonderful if we could get our deer back down to pre-Columbian population levels estimated at fewer than ten per square mile versus the current estimates of 25 to 35. Not only would it relieve the pressure on our planted landscape, but it would also allow our native woodlands to regenerate with more bio-diversity. Eating more venison is one strategy, but here are others that might discourage the deer from feasting on your yard.

Deer fences and netting

Barriers are essential when "your" deer are really habituated and come home every night. Many Carlisle landowners erect high and/or electric perimeter deer fences along their lot lines. Although these are pricey to build and maintain, they are well worth the investment for many planted landscapes. One important little engineering detail to remember is a gate to let you (and not the deer) come and go.

Fencing individual plants or groups of plants is effective, too. I favor metal pipe posts that can be pulled out during the summer when the browsing pressure subsides and your plants are off the deer's menu. Netting also works, but heavy snow and aggressive deer can shift it around wooden clothes pins help keep it in place. Burlap works well and also protects the plants from winter burn.

Repelling the deer

Offensive scents, tastes and noises are often used to deter the deer. In general, scent methods do not work on tasty shrubs out in the open, but the right application might discourage a deer from jumping a fence or remind it that it doesn't really like your plants anyway. It's wishful thinking to just hang a bar of soap or vial of coyote urine on an otherwise unprotected holly that the deer have been enjoying.

Spraying plants liberally and frequently with repellents with alternating "flavors" works well.

The deer leave their unmistakable tracks in the snow.

The idea is not to make the plants completely inedible, but rather to encourage the deer to check out what your neighbor is offering. There are many different off-the-shelf formulations sold and in my experience they all repel, although they vary in strength and persistence on the plant. The key is in the "liberal application," which might take two gallons for some landscapes. A small, pressurized one- to two-gallon spray tank works much better than a quart-sized spray bottle. Buying concentrate in quantity helps keep the price down, but even at commercial volumes these formulations are expensive. Depending on the weather, deer patterns and formulations, you might need to apply every month during the dormant season; if you have deer year round, you'll need to reapply as plants grow.

Home-cooked repellents

I've enjoyed reasonable success reverse-engineering commercial repellents and cooking up some truly foul (but edible by deer) stuff right in the kitchen in ten-gallon-plus batches. The materials are cheap and for the most part readily available. Do a little research on the web and be creative (see for ideas). I think of three major components: first is a bad taste, something like black pepper, and second is scent — "rotting flesh" is the benchmark. Eggs are the most common ingredient followed by dried cow and pig blood, which apparently tell the deer that predators are nearby. The third component is a "spreader-sticker," composed of a soap/oil/wax-type compound. The spray must stay on the plant to do some good, but you also have to make sure that your mix will flow through the sprayer.

Other defensive strategies

Motion detectors connected to lights, radios, air cannons or water sprays are said to be quite effective, but you need either a lot of land or really tolerant neighbors. These active defenses might be best reserved for vegetable gardens. Dogs ? The deer know there are few 24/7 dogs in Carlisle.

The defensive strategy employed by many shrubs is to produce bitter compounds similar to those that broccoli uses to fend off children. This varies considerably even within the same plant species. One naturalist explained the spotty browsing behavior as a deer's way of making sure it never overdoses on any one specific toxin.

There are many published lists on the Internet ranking the desirability of landscape plants for home gardeners, and for the most part these seem to be appropriate for Carlisle. Winterberry and highbush blueberry are two of my favorites for being deer resistant and native and working well along the woodland edge. New plantings in the spring might deter the deer from devouring your property next winter.

John Bakewell is a Massachusetts Certified Arborist living in Carlisle.

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