What’s in Bloom

9, Dec, 2010 Rose Kennedy Greenway Conservancy

As autumn comes to a close, our perennials have gone dormant, the fall-flowering bulbs have finished their display, and all but a few of our deciduous trees and shrubs have lost their leaves. Though a selection of ornamental grasses and perennials still remain attractive and are left standing throughout the winter.  The task of keeping the park green falls to conifers such as Pines, Firs and Spruces, and broadleaf evergreens such as Rhododendrons, Andromeda, Boxwoods, Hollies, and Inkberries.

Frasier Fir (Abies fraseri), found in many homes for the holiday season.

Though broadleaf evergreens remain active throughout the winter, the low temperatures and shorter day lengths cause them to metabolize at a significantly lower intensity and rate than in the hot summer. One of the biggest health hazards to a broadleaf evergreen is that of desiccation, or drying out, of the leaves. The leaves struggle to retain moisture in order to stay alive, but as the harsh winter winds blow over the leaf surface, the moisture is slowly whisked away, and the plant is unable to restore the moisture as effectively as it can in the summer since the ground is now frozen. Many home gardeners will notice an orangeish tint to their Boxwood Hedges, or spotting of dark brown and dead leaves on their Inkberries. These are leaves which have dried out and died, and though the plant can generally regenerate them the following spring, it remains sickly looking throughout the rest of the winter, and often leaves the plant at risk for other health problems due to its weakened state.


Inkberry (Ilex glabra ‘Densa’)

Many parks and homeowners use a product called an “anti-desiccant” to help stay this process and keep the leaves of a broadleaf evergreen as green and healthy as possible throughout the winter. The anti-desiccant is usually derived from either petroleum or natural plant oil, and once sprayed onto the leaves of a plant, essentially functions by covering the leaf with a thin, waxy membrane which is impervious to water. It is particularly important to cover the underside of the leaf with this substance, as the stomata, pores for water vapor and gas exchange, are located here. With this waxy membrane added to the leaf surface, the leaves are able to hold their moisture more effectively and are less at risk for health problems stemming from desiccation.

Anthony treating Boxwood

Anthony treating Boxwood (Buxus ‘Green Velvet’) with anti-desiccant.

The waxy membrane produced by an anti-desiccant treatment will not last forever, and horticulturists usually strive to make three applications over the course of the winter. The first application takes place as fall turns to winter, which many horticulturists time around Thanksgiving. They will then strive for two follow-up applications, generally in early January and February, at a stronger concentration than the first application. It must be above 35˚F for an anti-desiccant application to effectively adhere to the plant, so a horticulturist will generally strive for the narrow window of a warm snap or thaw in the mid and late winter to make their follow-up applications.

Often underappreciated or overshadowed during the warmer seasons, broadleaf evergreens tend to really come into their own over the cooler seasons. Though this process may leave some thinking they’re more trouble than their worth, a healthy Holly Tree bearing fruit in the mid-winter or Andromeda preparing to flower as winter comes to a close is a good addition to any park or garden, and well worth the extra effort to keep them looking their best.


Winterberry (Ilex verticillata)

You will be able to spot these beautiful forever green plants when you come out to the Greenway to celebrate winter with us. We’ll be lighting up the parks for Bright Lights for Winter Nights on Tuesday, December 21 from 4 – 7PM. Visit our event page for more details.