Give plants protection they deserve

Believe me when I say I don’t have any special ins when it comes to predicting winter weather in the Inland Northwest. However, after going through 27 winters, the early rains and snow in the mountains indicate that a few minutes spent protecting our broadleaf evergreens and conifers may worth it this year.

First, make sure all plants have a good long drink of water before the ground freezes. The rains and cooler weather through the fall have gone a long way toward rebuilding soil moisture, but have not completely soaked the deep soil horizons.

“Use pine needles to insulate the roots of plants that are marginally hardy,” says Joe Zubaly of Northwest Plant Health Care, “including Hinoki cypress, rhododendrons, azaleas, laurels and hollies.” This protects the roots from freeze-thaw cycles. Zubaly adds that you can use other mulches but, “pine needles drain quickly and don’t soak up moisture.”

Evergreens like yews, upright junipers, cypress and some taller boxwoods that have very upright branch structures can benefit from being carefully tied up for the winter. Zubaly suggests using green plastic nursery tape wrapped loosely around the entire plant. He doesn’t like to use twine or wire because if the tie is forgotten, it can eventually cut off the plant’s or branch’s circulation. The nursery tape also stretches with the plant and will break down in the sun after a couple of years.

Zubaly doesn’t recommend routinely tying up shrubs though.

“If you keep something in the tied position it won’t develop the cellular growth that then supports plant’s weight,” he says.

As branches sway and bend to the forces of nature, they build strength much like we do when we lift weights. If you do wrap them, Zubaly suggests removing wraps early in the spring and tucking any wayward branches back into the canopy with a little nursery tape.

“They will resume their place in the tree much more quickly this way,” he says.

If we do get a heavy wet snow or ice storm, Zubaly suggests going out and gently shaking overburdened branches to remove some of the weight. Avoid pulling or pushing up and down on branches because the branch may be just at the breaking point, so this could actually cause more damage.

Strong winter winds and frozen ground are hard on some marginally hardy varieties of rhododendrons, laurels and hollies. Their leaves transpire throughout the winter albeit at reduced levels. When a strong wind blows across the leaf surface, it gives up moisture quickly. Under the right conditions, if the ground is frozen, the roots have no way of replacing that moisture and the leaf basically dries out. We see this as brown edges or entire brown leaves in the early spring.

Some plants adapt better to this than others. PJM rhododendrons are hardy down to -25 degrees here for two reasons. They have a relatively small leaf that rolls up when it gets cold. This reduces the surface area exposed to the elements and the potential loss of moisture. This rolling mechanism is so pronounced that I can almost guess what the outside temperature is simply by looking at some PJMs I have near my front door.

A variation on this problem is sunburn on evergreens. Sometimes the sun pops out on those warmer than usual winter days and thaws out plant tissues on the south side of the plant enough to bring water into exposed cells. When the temperature drops at night, this water freezes and destroys cell structure.

There are several ways to cut down on wind-driven desiccation and sunburn. Burlap can be placed around susceptible plants to break the force of the wind and shade the plant from the sun. The burlap can be purchased in sheets or rolls at some garden centers. Drive wooden stakes into the ground a couple of feet away from the plant and then staple the fabric to the stakes. In the spring, pull up the stakes and roll up the screen for storage. Do not use plastic because there is a possibility of the plastic laying on the plant and suffocating or cooking it.

You can also reduce transpiration by spraying leaves with an anti-desiccation sealant. Products like Wilt-Pruf are organic bio-degradable compounds that put a flexible layer of desiccation protection on the leaf surface. They break down in time for spring growth and do not impact plant growth. If you choose to use on of these, Zubaly recommends applying it as directed on the label over the course of the winter to keep the coverage at full force.