How Do I Protect Plants from Frost?

Gardening expert and certified wit Felder Rushing answers your questions and lays down some green-wisdom. You can get more of your Felder fix at www.slowgardening.net.

Question:

Every winter my neighbor wraps her boxwoods with burlap to protect them from a frost, but it looks weird to me. And anyway, when leaves on my shrubs get brown in the winter, new growth seems to come out just fine in the spring. Would it really help to wrap my shrubs?

Answer:

Most winter injury to plants is from them drying out in cold wind or from bright sun when roots are frozen, or a combination of the two.

I would hope that most folks plant tough shrubs for their part of the country to begin with, and keep them healthy through the summer with nice deep soakings for good roots, and reasonable fertilization to keep foliage and stems tough. These are the most important three tips for helping plants through the winter (or summer, for that matter).

And by the way, too little water and fertilizer can cause plants to be weak; too much or too often can make them lush and tender and more sensitive to freezing.

For extra protection, soak plant roots before really cold weather freezes the ground and roots, and cover the soil with bark, straw or other loose natural mulch.

Still, sometimes when the ground gets frozen and roots can’t pump water to twigs and leaves, a cold, steady wind or lots of sun can dry plants out and cause leaf burn and twig damage. This is when wrapping shrubs or putting up a windbreak can make a difference.

Different Strokes

There are several fairly reliable foliage sprays on the market which, if applied and allowed to dry before a freeze, can protect plants from drying and freezing — to a point. They can last several weeks, but will not help during deep, hard freezes.

Or simply shield plants with screens or by loosely wrapping individual plants. It is important to use materials that still allow for some light and some air circulation, or plants can get diseases.

While some loose-weave synthetic wrapping material is available, most folks use an inexpensive burlap, available at many garden supply stores. Both materials cut down on frost and sun damage while remaining permeable enough to allow in some sun and rain without cutting off air circulation (which could lead to diseases).

Windbreaks and Teepees

While not much can be done to protect a hedge of medium to large shrubs, you can protect a row of small shrubs with snow fencing or burlap strung between wooden posts or sturdy canes stuck in the ground at regular intervals. Putting it in a zig-zag pattern can make it sturdier and provide better protection than running it in a straight line.

For individual plants, stick three or four posts or canes into the ground around the plants — leave a few inches between the plants and the posts — and tie the tops together for strength. Wrap with two or three loose layers of burlap, but be sure to leave a flap that can be opened during average or warm winter weather, and closed only during severe wind or freezing temperatures.

Question:

This summer and fall the leaves of my shrubs turned black with something sticky. What caused this, and can I keep it from happening next year?

Answer:

This is going to sound terrible, but that black stuff is actually a fairly harmless mold that is growing on the excrement of aphids and other small insects that suck sap from the undersides of leaves and drip sticky, partly-digested plant sugars below. It’s called “honeydew” — don’t look up with your mouth open!

Most of it will shed over the winter, or you can wet the plants down with a mild soapy solution, let it dry a few minutes to soften and loosen the honeydew, then rinse with clear water. It should start to flake off within days.

To keep it from happening next year, use an insecticide labeled for aphids and spider mites — there are some natural products that do this very well, including “insecticidal soap.”

It does no good to spray ahead of time, so be prepared to start spraying at first signs of the problem next summer. Make sure you cover the undersides of leaves, where the bugs are, and repeat once or twice a few days between sprays to catch any you may have missed with the first application.