Even Oregon evergreens can suffer from moisture loss.

Byline: Gardening by Sarah Robertson For The Register-Guard

A GARDENER'S annual autumnal rite of `putting the garden to bed' for the winter often fails to recognize that evergreens, like reluctant toddlers, simply refuse to sleep.

While much of the garden slumbers compliantly, safely dormant and secure against the ravages of wind chill and frost damage, evergreen shrubs and trees continue to respirate and photosynthesize. Western Oregon's occasional stints of warm, sunny weather offer an opportunity for these species to revitalize their energy systems. Our much ballyhooed rainfall is especially appreciated, allowing still-active root systems to pull moisture into thirsty tissue.

This subtle yet amazing process allows evergreens to look great despite seasonal fluctuations that force most perennial species to fold up shop during the winter.

Evergreens aren't totally immune to problems associated with winter weather. Cold and drought tolerance among certain species becomes quite pronounced when temperatures drop below a tolerated range or a lack of moisture threatens.

Penetrating cold forces certain broadleaf species such as rhododendrons and viburnums to roll up their leaves into tight rolls in an attempt to conserve moisture. Conifers are typically tougher, but they, too, can suffer needle drop or worse when conditions become too wet, dry or cold.

Since the goal is to keep our plants happy, it's helpful to gain some understanding of evergreen physiology and just how these plants manage to make it through the winter intact.

While cold tolerance is important, experts say that getting and retaining moisture is the most critical winter requirement for evergreen species. Mother Nature has given them a number of coping strategies, most of them the result of leaf type and shape.

Here, conifers are the big winners over broadleaf evergreens. Needle design, whether long and flexible (white pine) or short and stubby (Norway spruce), helps minimize moisture loss. The close spacing of these needles creates a nearly airless boundary around the leaf pores (more correctly called stomata), which are typically found on the bottom side of both needles and leaves.

Since it's more difficult for wind and cold to penetrate into this area, moisture loss from evaporation is much lower than might otherwise be expected.

Broadleaf evergreens are more susceptible to winter's wrath, simply because there is a great deal more leaf exposed to the elements. Since the stomata are located on the bottoms of leaves, it makes sense when species such as rhododendrons curl their leaves downwards in an attempt to protect their pores from further moisture loss during periods of especially cold weather.

Although the curl is occasionally permanent, usually the affected leaves return to their normal shape with the reappearance of warmer weather.

Last spring, a friend with more than a dozen curled-leaf rhododendrons was starting to worry. The initiating cold spell was a distant memory, but you'd never know it from looking at her plants. She had watered deeply several times with no effect, warmer weather didn't seem to be doing the trick and visions of rhododendron death filled her dreams.

In a last-ditch effort to snap her plants out of their funk, my friend applied two doses of high-quality rhody fertilizer about 10 days apart. To her surprise, every single curled leaf straightened and plumped up within three weeks - an amazing success given the lackluster appearance of these stately rhododendrons (all of them at least 25 years old) just one month earlier.

The basics of good health during the winter isn't difficult. You just need to satisfy their moisture requirements and, in the case of broadleaf species, protect favorite susceptible species from extreme cold.

If you have plants located beneath eves or under the canopy of taller evergreens, dig gently around the root zone at least once a month. If the soil feels dry, turn on the hose so that a gentle trickle of water can slowly saturate the area.

I also always check susceptible plants if I hear a weather report calling for subfreezing temperatures. A moist root zone seems to help evergreens cope more effectively with extremely cold and/or windy conditions. Mulch the root zone with bark chips to retain moisture while simultaneously improving the soil.

Anti-transpirants are available from some garden centers. Typically sold as a canned spray, these type of products are designed to reduce moisture loss during stints of subfreezing weather. Some gardeners swear by them, others contend they're worthless. It probably depends on the individual plant, its location and myriad other factors.

I've used them in the past with a fair bit of success, but only on select plants. They have never harmed any of my plants, so my recommendation is to keep a can on the shelf to use on especially treasured evergreens in your garden.

Keep a roll of burlap or row-covering material on hand for extended periods of cold weather. These products can be easily wrapped around even large specimens to provide protection from both wind and cold.

It may be December, but for those of us with lawns, the chore of mowing is still a reality. Growth has definitely slowed, but it's likely that lawns will need at least one or two more trims before you can give your mower (and yourself) a well-earned - but all too short! - break.

Pick a time when the lawn is least soggy. Walking and mowing when things are wet can compact the soil, which isn't good for a lawn's root system. Set the mower blades a bit higher to avoid scalping, which seems to occur more easily when conditions are damp.

Sprinkle the clippings in a thick layer around garden beds to give borders a slow-release nitrogen boost.

Winter rains tend to leach nutrients from the soil at a surprisingly fast clip, so this added nutritional boost is sure to be appreciated even if plants won't take full advantage of it until next spring.

I've also been known to fertilize our lawn in December. A bit unorthodox, but I use a slow-release organic blend that seems to do a fine job of improving both color and texture.

The concept isn't totally off the wall. The darn grass is still growing, albeit slowly, so it makes sense that it would benefit from a bit of food if it's looking sickly.

Sarah Robertson of Eugene writes a weekly gardening column for The Register-Guard.