Garden Notes

Winter Gardening

By Abigail Higgins - February 2, 2006

Two more weeks of mild weather has brought us to Groundhog Day, Candlemas in the old peasant year. Probably increased snowfall and coastal storm systems will ensue, as well as many bright and sunny February days. But if not, this could mean the addition of winter as a fourth gardening season, in addition to spring, summer, and fall. If this pattern becomes the norm and if we were to experience winter routinely more as they do in the Mid-Atlantic States, we would want our gardens to contain more plants of winter interest.

Which brings me to the witchhazels in bloom at the Polly Hill Arboretum. Bob Childs, of the University of Massachusetts, after his well-attended talk on caterpillars and moths at Agricultural Hall on Jan. 24, led an outdoor insect pest workshop the next day at the arboretum. Under sunshine and blue skies, the blooming witchhazels stood out brightly. Three in particular demonstrated their cheerful earliness: Hamamelis mollis, the Chinese witchhazel, and the cultivars H. x intermedia 'Gold Crest' and 'Ruby Glow.' Chris Wiley of Vineyard Gardens, one of those participating, remarked that she would like to sell more witchhazel but is challenged to acquaint the gardening public with them. Their period of bloom does not coincide with typical nursery visits, and even their outstanding fall coloring is apt to be missed.

The witchhazels in general are quite well adapted to Martha's Vineyard, with H. virginiana, the medicinal species, considered native. Up-island stream banks are good places to find H. virginiana, which typically grows with two or three stems to form a spreading shrub or small tree. (However, I planted one on a somewhat dry, west-facing hillside where it is doing well. An unmarked witchhazel cultivar blooms at present in the greenbelt at the West Tisbury post office parking area.)

Off-season delight

Although they grow as understory plants in moist mesic forests, witchhazels will bloom most profusely where they can be sited in an open position; but partial shade is no impediment to flowering. The blossoms are particularly effective if they can be viewed at some point during the day when backlit by the sun. They also possess an enticing fragrance, ("honeyed" is the well-deserved cliché) which they pump out periodically during the course of warmer days. A shrub border with well-prepared humus-rich soil is the perfect place for a small collection. The fragrance will provide a special winter bonus if witchhazels are planted close to the house.

Such a collection on its own is a good winter garden feature, but combined with an under-planting of hellebores (the early H. foetidus and H. argutifolius,) and ericas (the January to March blooming spring heaths) it becomes something special and interesting for winter days. The witchhazel root system tends to be shallow and wide, so effort should be made not to disturb it by whatever cultivation is needed for the under-planting. Hellebores likewise would prefer to be undisturbed. If we achieve Mid-Atlantic climate status, then add the winter iris, I. unguicularis (or gamble now with a protected southern exposure). A nice compost mulch, applied to the depth of an inch every year, will help keep the roots in the kind of soil that witchhazels and hellebores alike require - moist and humus-rich.

For those in search of reference books for winter gardens and color, and an all-around good book to have on your shelf, I recommend a book I have, Adrian Bloom's Year-Round Garden, (Timber Press, Portland OR, 1998) In it is a great deal more information about seasonal gardens than what I can squeeze in here. There are many other possible winter-interest plants to tempt the gardener into outside activity.

I want to return for a moment to Bob Child's informative caterpillar and moth talk on Tuesday night, for which thanks go to the Vineyard Plant & Landscape Association, Polly Hill Arboretum and Martha's Vineyard Agricultural Society. Go to his web sites, www.umassgreeninfo.org or www.pronewengland.org for lots and lots of good insect information.

Bob emphasized that, due to known and unknown factors, six separate species of caterpillars and their moths are experiencing population explosions here, constituting what could be a real multiple-whammy for trees in affected areas of the Island. The species in question are winter moth (Operophtera brumata), fall cankerworm (Alsophila pometaria), spring cankerworm (Paleacrita vernata), forest tent caterpillar (Malacosoma disstria), eastern tent caterpillar (M. americanum), and gypsy moth caterpillar (Lymantria dispar).

Bob talked about each species, showed slides and endeavored to teach us how they are separate and discrete, despite their confusing similarities. Each species has its own distinct period of pupation, larval stages, parasitoids, egg-laying behavior and mating cycle. Each species hatches once. Though it may appear that there has been a later, second hatch, this would be another species making its appearance; the two cankerworms and winter moth, in particular, appear very similar. The ultimate seriousness or end result is subject to variables of moisture, temperature, degree days, and general weather events, so we will not know until the onslaught is almost over just how much trouble our trees will be in.

Moth brawls
But we appear to be on course for a dismal, heart-wrenching spring, as far as our woodlands are concerned. If spraying of property or choice trees is part of your plan, discuss this now with the licensed personnel! By the time caterpillar activity is visibly apparent, the window of opportunity for effectiveness of the pesticides available may have passed or diminished, and you will be waiting at the end of a very long line. Generally speaking, not only are the available products more effective on the younger instars (stages), but the trees will experience cumulatively less damage. However, all property owners should understand that spraying effectively against one caterpillar pest guarantees no protection against the next caterpillar pest to hatch, the one after that, or those that balloon in from elsewhere. It is admittedly a discouraging prospect.

A postscript to the dramatic Dec. 9, 2005 weather event comes from the Cape Cod Times of Jan. 18, 2006. The meteorological explanation is that it was caused by jet stream air, flowing west-to-east high above North America at over a hundred miles an hour, which encountered an obstructing warmer low-pressure system. The warmer air mass caused the fast moving, cold, dense, high altitude air to divert beneath it and essentially to dive-bomb the landmass that lay below, Cape Cod. Apparently this is a rare occurrence, happening maybe three or four times in a century, according to Don McCasland, program director at the Blue Hill Observatory in Milton. The recorded pressure drop was one of the steepest that Island barometer watchers had ever seen.