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!

The Plant Man is here to help. Send questions about trees, shrubs and
landscaping to . For resources and additional
information, or to subscribe to Steve's free weekly e-mailed
newsletter, go to www.landsteward.org