Protect plants from winter's cold and frost

At this time of year, as evenings become a little more chilly, we can keep out the cold by pulling on a sweater or snuggling into a warm jacket as we brave the night air. But remember that plants feel the cold, too, and you can help them bundle up and stay protected against the coming winter weather.
One major problem that can harm your perennials is when the ground freezes then thaws then freezes again... and again. This can happen even in quite temperate regions during an unusually severe winter, and of course in some regions every winter could be called severe!
Plants subjected to repeated freeze-thaw-freeze conditions tend to "heave" their roots out of the soil where they can become frost-damaged. Mulching your plants can help protect them against the effects of freeze and thaw. There are plenty of choices when it comes to mulch, including straw, shredded bark and pine needles. One major benefit of straw is that it is hollow, allowing an effective layer of insulation without being too tightly packed.
Apply a winter "coat" of mulch about 3 to 4 inches deep around each plant. (If the plants are in an area that is unprotected from the elements or open to strong winter winds, you can safely add an extra inch or two of mulch.) Then gently pull the mulch back from the stem or truck with your fingers. This allows the plant to breathe and helps diminish the likelihood of disease problems.
Don't make the mistake of adding the protective winter mulch too soon!
My best advice is to wait until after the first really freezing cold night, but before you expect any possible snowfall. Why wait? Mulch too early and you could be providing comfortable nesting areas for rodents that might chew on the plants you're trying to protect.
It isn't just the roots that can need some protection against the elements. A particularly hard frost can cause "above ground" damage, too. There are various commercially-made plant covers available from catalogs and garden centers. They are made from weather-resistant polyethylene and secure around the bottom with pull-tabs. Available in various sizes, they are fairly easy to slip over the top of the shrub or bush.
If you prefer to get creative, you can use lawn and leaf bags, and I've even seen sheets of bubble wrap shaped into plant covers. Plant covers should only be used when you are expecting a severe frost that could damage delicate plants. Remove the covers as soon as the immediate danger has passed. Do not leave plants covered for extended periods.
In the fall and winter, it's not just cold weather that can attack your plants. Deer, rodents and other wildlife can cause quite a lot of damage, too. In a future column, I'll discuss how to keep your plants off the all-they-can-eat "critter buffet."
In a recent column, I included a letter from a reader who had brought some hibiscus seeds from Canada to her home in the US. Another reader, David A. Bequeaith, who saw that column, took me to task for not pointing out the potential problems that can result from bringing flora into the United States from foreign countries.
As a general rule, the USDA warns against importing foreign plants, and in some cases, ignoring these warnings can result in heavy penalties. Over the years, I have worked extensively with the USDA, often addressing issues relating to the import and export of plant materials. Indeed, I should have mentioned the potential problems and inadvisability of bringing in plants from other countries.
So my advice to those who might be thinking of bringing seeds with them from a foreign trip: If you are in any doubt at all about the legality and safety... Don't do it!
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