In all the wide range of garden operations, there is probably none less understood than winter mulching.
9 out of 10 gardeners continue to use rule-of-thumb practices—some of them actually harmful—with no real knowledge concerning what should be done or how to do it.
Testing Of Roses
In a Chicago Regional Rose Society survey, in which 8,464 roses in 50 rose gardens were tested, winterkilling of “billed up” roses were at least three times as great as where no protection was attempted.
Hilling, if properly done at the right time, may be helpful, but under many conditions, it is not.
In our old garden near New York City and now at our new one at Cape Cod, we have better results without hilling up.
Nature Of Winter Killing
Not until one understands the nature of winterkilling and its causes is he in a position to know how to guard against it using mulches or other means.
Basic Cause Of Winterkilling
The basic cause of winterkilling lies within the plant’s physiological and hereditary makeup.
This varies not only with different species but in varieties and horticultural subvarieties of the same species.
Some naturally survive arctic conditions, while others perish at the slightest frost.
Resistance to cold is “bred in the blood.”
Winter Mulching For Semi-Hardy Plants
Between these two extremes, there is a wide range of semi-hardy plants or “hardy with protection.”
Winter mulching plays such an important role in the culture of these.
Two Kinds Of Winter Killing
Winterkilling is of two kinds:
- Freezing or near-freezing of the tops
- Freezing of the roots
Either may result in the plant’s immediate or eventual death.
Scientists tell us that winterkilling from freezing is most likely to occur when wood or stems are still in active growth, weak from undernourishment or disease, subject to alternate freezing and thawing, desiccated or drained of moisture.
Four Objectives In Protecting Shrubs Against Winter Injury
Consequently, in protecting shrubs or other plants against winter injury, there are four distinct objectives:
- To have the above-ground growth well matured and hard:
- To keep the plant in a vigorous, healthy condition;
- To prevent alternate freezing and thawing of both roots and top growth; and
- To avoid, so far as is possible, desiccation of the above-ground growth by the hot sun (in late winter and early spring) and high winds.
Concerning the production of healthy, vigorous growth, it is too late to do much of anything during the balance of the present season.
Fertilizers applied now (except slow-acting ones such as superphosphate and potash salts) may stimulate new growth and thus do more harm than good.
Nor can much be done at this time to help harden the season’s growth of new wood, except perhaps to withhold water to allow the soil to dry out.
Two Things To Do To Lessen The Danger of Winter Killing
Two things can be done now to lessen the danger of winterkilling:
- Prevent alternate freezing and thawing below ground (mulching), and
- Protect top growth from desiccation or drying out.
Two Misconceptions In Mulching
Before discussing mulches, let’s dispose of two misconceptions concerning them;
- First, mulches are not applied to keep out the cold but to keep it in.
- Second, a heavy mulch is not better than a light, fibrous one, so long as the latter stays put once it has been applied.
Ideal Winter Mulch: Snowing
Snow is the ideal winter mulch. It is nature’s blanket that admits air, insulates the soil against fluctuations in temperature, and prevents drying branches and stems.
Many plants winter hardy in regions where snow remains unmelted for long periods and perish in much milder climates without snow.
While snow is the ideal mulch, it cannot be had for the asking, so here are some of the materials we can use in its place.
All should be applied 2” to 4” inches deep over perennial flowers and around shrubs and trees after the ground has frozen to a depth of from 1” to 2” inches.
Bagasse Or Shredded Sugar Cane
Bagasse, or shredded sugar cane, commonly sold as chicken litter under various trade names, is coarse in texture, stays in place, remains loose and springy, admits the ready passage of rain or melting snow, and gives effective insulation.
We consider it about tops for both summer and winter mulching.
Leaf mold, as well as partly decomposed rough compost, possesses many advantages of bagasse but is less uniform in composition and not nearly as permanent.
Wood chips are now available in many localities and are somewhat similar to bagasse but are likely to heat up if applied too thickly when fresh.
With its use, high nitrogen fertilizer may be applied in spring to offset the loss of nitrogen from the soil as the chips decompose.
Leaves of hardwood trees, such as oak, make a good mulch for perennials and biennials.
However, the leaves of poplar, maple, and other softwood trees pack down into a wet mass are taboo.
Leaf mulches—except when used for azaleas, rhododendrons, and other low-growing shrubs—need to be held in place with evergreen boughs, brush, or chicken wire.
Pine needles are good, attractive, can be left on for summer, and are especially useful for wildflowers or rock garden plants.
Peatmoss: Soil Conditioner
Peat moss, unrivaled as a soil conditioner, is not desirable as a winter mulch as it tends to form a wet blanket.
Buckwheat hulls have good insulation qualities and are top in appearance.
They afford no nesting place for mice and are our favorite mulch for bulb beds and fall-planted perennial and biennial seedlings.
Excelsior is light, protects soil and foliage from direct sun, and never packs. Its insulation value is low.
We find it most useful for wintering seeds in a cold frame.
Useful Materials For Wintering Seeds
Other materials often locally available are:
- Salt or bog hay is good for shrubs and small trees. etc., difficult and messy to remove and a fire hazard;
- Sawdust (if coarse) is good for small plants, lilies, and acid lovers; if not removed in spring. Use a nitrogen fertilizer;
- Seaweed and or eelgrass (dried), excellent but not attractive;
- Cranberry vines, a springy mat, attractive, excellent especially for low perennials, subshrubs, and semi-hardy bulbs.
44659 by F. F. Rockwell