Newsworthy from our nursery

Evergreens Take Freezes in Stride

Some interesting strategies to fight the cold

How do hardy perennials survive very cold and fluctuating winter temperatures? Basically, there are 3 ways. The first is to go dormant and die back to the ground completely. Overwintering parts like roots, rhizomes, and next year’s buds, are underground where they stay protected until soil temperatures warm in the spring, and the plant receives signals to break dormancy and start to grow. Many of our favorite spring bloomers like blood root, trillium, Jack in the pulpit, and Virginia bluebells do this.

The second option that many deciduous plants use is to drop all leaves and go into a resting or dormant state during the winter. Since there are no leaves, there is little need for water, and these plants essentially stay asleep for the winter. Warm temperatures send the signal to resume growth. Bluestar, baptisia, bleeding hearts, and purple conefower behave this way.

But evergreen plants, whether they are shrubs, trees, perennials, or vines, have issues that must be addressed throughout the winter months. Rhododendron, Florida anise tree, Christmas fern, seersucker sedge, beardtongue, and succulents have special features and adaptations that allow them to tolerate some degree of freezing and thawing.

Since evergreen plants keep their leaves, there is always a need for water that must be supplied primarily from the roots. If that water freezes anywhere along the supply chain or within or between plant cells, there may be big trouble. Water expands when it turns to ice which takes up room, and when the ice thaws, cells may break apart, bubbles may form where they shouldn’t, and plant tissues may break apart. Luckily, evergreen plants that are cold hardy in your climate zone are equipped to handle these assaults if they have been properly prepared.

Here are steps you can take to optimize the chances that your evergreen plants will make it through the winter in great shape.

Choose plants that are hardy to your climate zone. Refer to our plant descriptions and to the USDA plant hardiness zone map if you are not sure.

Be sure to plant in a site where the plant should thrive. Soil type, drainage, and light exposure are critical.

Any pruning should have been done when it did not promote a fall growth spurt. Likewise, fertilizing should be stopped by late summer/early fall allowing for proper hardening off.

Plants must enter winter with adequate soil moisture. A 2-3” covering of mulch can help conserve water. And plants must not be water-stressed before a freeze. Water, if necessary, if temperatures are forecast below 23 degrees.

Protect susceptible plants like rhododendrons and hollies from dessicating winds. All evergreens loose water through their leaves and cannot replenish that water if the soil is frozen. Again, keep the soil moist, apply a good mulch, and plant in a protected place or along a southeast, east, or northern side of a wall or fence. Evergreen boughs or burlap can be used as a temporary cover. Rhododendron leaves will droop and curl downward to restrict water loss. And many perennials will let their leaves lie flat on the ground, all ways to conserve water.

Lastly, there is nothing like a nice, light snow cover to protect your plants over the winter. A 6” blanket of snow moderates temperature swings and keeps the soil moist. Now if we could just keep in on the garden but off of the sidewalks and streets!

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