Keeping evergreens alive through the winter begins during the growing season, by paying attention to choosing plants carefully, selecting the right location, and watering adequately.
You can head off many winter injuries in evergreens by choosing plants appropriate for New Hampshire's USDA Plant Hardiness Zones 3-5.
Winter winds and sun can be extremely damaging to evergreens, so plant them in protected spots out of prevailing winds.
Additionally, avoid late summer or early fall fertilizing, as this stimulates new growth that can't tolerate cold winter temperatures.
Foliage discoloration is one sign of distress in evergreens. Broadleaf evergreens, like rhododendrons, lose water through their leaves and can’t replace it via the roots when the soil freezes. Brown, burned leaves and needles are a common occurrence in the late winter months.
In order to prevent this, try creating a wind break with materials like burlap or canvas. Attach material to a frame or directly wrap plants. Never use black plastic as it causes damaging temperature fluctuations.
Prolonged cold snaps or periods of freezing and thawing can damage plant roots. Mulch evergreens, especially those that have been newly planted, to insulate the soil and protect the plant roots. At least 2 inches of woodchips or straw should be applied over the root zone.
If you are seeing breakage from heavy snow and ice loads, placing wooden frames over your plants can keep them from getting crushed by accumulating snow and ice. At a minimum, brush off heavy snow with a broom if you notice particular strain on the limbs.
Plants near the road can be vulnerable to road salt injury. Salt spray causes needles to brown, which will be evident in late winter and early spring. Salt can also injure roots.
Avoid using rock salt on walkways near evergreens. Sand or saw-dust are the best choices. Alternative de-icing salts composed of calcium chloride or calcium magnesium acetate can be used sparingly. Burlap or canvas barriers can reduce injury from salt spray.
If you have a question for us, you can send us an email or voice memo to Homegrown NH@NHPR.org.
See you in the garden!
Homegrown New Hampshire is a collaboration between Squam Lakes Natural Science Center and NHPR.
