Q. How does wind affect the growth of plants?
Wind greatly affects plants throughout their growth. When plants are seedlings, slight breezes help them grow more sturdy. Wind at gale force can damage or even break and blow down the strongest tree. Depending on where in the world you live, this storm damage can occur in winter, summer, fall or early spring. Winter wind is particularly damaging because plants are unable to replace the water they lose and become desiccated. The process is similar to an ice cube left in the freezer--although it doesn't melt, it will gradually become smaller. In many areas, wind causes more winter plant desiccation than sun.
Persistent strong winds occur mainly in late winter. Temperatures then often begin to fluctuate between mild and severe. Mild days, especially several in succession, may lower the cold hardiness of some plants. When icy temperatures and strong winds follow, the damage may be especially severe. So even in late winter, it may be beneficial to place a wind screen on the south to northeast side of plants, or to mulch over low plants.
The "wind chill factor" heightens the effect of cold: 20°F with a 40-mph wind is as chilling as -10°F with a 5-mph wind. Plants located near the house, particularly on the east, get fairly good wind protection. Soil near the house usually does not freeze deeply and the east wall protects from late afternoon winter sun. The south side also offers wind protection, but excess warming of marginal plants in that location often causes damage. North sides of buildings allow some wind damage, but the protection from winter sun often enables certain plants to survive quite well there.
A burlap wind break supported with stakes provides protection from winter cold and wind. Or place a ring or wire mesh around each plant and fill it loosely with straw or oak leaves. Any materials placed around plants should be loose enough to allow some air movement. Antidessicants (wax emulsion spray), sold by nurseries, can also be used on some plants for winter protection. Apply anti-transpirants only when temperature is 40°F or higher.
Mulches as well as snow make good protection for plant roots. Mid-winter pruning of evergreen branches can provide mulch for any perennial plant that produces fall sprouts, for example chrysanthemums and oriental poppies. The branches will remain green most of the winter, making an attractive cover, and usually stay put in windy weather.
Plants vulnerable to wind include not only less hardy specimens, but also many hardy plants not adapted to open situations, including forest natives such as hemlock. Wind-whipped plants may suffer broken roots. Fruit trees do not bear when wind tears off the blossoms. Wind retards growth through increased cold, as seen in the "cold bands" on corn leaves when chilling temporarily halts growth, or through reduction of photosynthesis because less leaf surface is exposed to the sun. A 15-mph wind delays maturity of marigolds and reduces their flower size by 50 percent, according to the Oklahoma Agricultural Experiment Station.
Slopes present particular problems. A windbreak can be used to shut off the flow of cold air that occurs on even a slight slope, preventing its settling at the lowest point to injure plants there. An opening in plantings at the bottom of the slope is also helpful to allow cold air to drain out of the garden. Windbreak plantings can cut wind velocity by 75 percent or more, for a distance 10 times the height of the windbreak. The best windbreak plants are those that are densely branched to the ground, or multiple-stemmed with rough bark. A curving hedge on the north will turn aside wintry blasts, while in summer it catches and deflects through the garden much-needed cooling breezes. These breezes can also be accelerated by channeling them through openings in south and west plantings in.
Windbreak plants that grow tall and narrow or can be trimmed to narrow are highly useful in limited garden spaces. A few are suggested by Dr. Donald Wyman of the Arnold Arboretum (Jamaica Plain, MA): American arborvitae, Thuja occidentalis; Populus alba 'Pyramidalis'; red cedar, Juniperus scopulorm and J. virginiana; common privet, Ligustrum vulgare; fastigiate European hornbeam, Carpinus betulus 'Fastigiata'; and "Tailhedge" buckthorn, Rhamnus frangula 'Columnaris'.
Bebe Miles, in Organic Gardening (Emmaus, PA) makes this wise suggestion: where winter winds really rage, select windbreak plants which are hardy for several hundred miles north of your area. That cold-weather adaptation should really help garden plants in inclement weather.
In some older larger trees with large spread branches or many branches, proper pruning, cabling and the shaping by a tree arborist will help prevent damage by winds.
For tips on a variety of gardening topics, see our Plant Information Guides.
- Courtesy of NYBG Plant Information Service