Winter Plant Protection in the Northwest

by Rod Smith, Oregon Certified Nursery Professional

© 1998-2016 Rodney A. Smith
All rights reserved.
Site Map

Winter weather can cause much damage to a landscape. Winter in the Pacific Northwest can bring excessive rainfall, cold temperatures, and drying winds. Normal winter weather stresses plants, and severe weather can kill or disfigure them. However, there are several steps that can be taken to prevent or minimize winter damage.

Rainfall is normally beneficial, but too much at a time can cause trouble. When the soil becomes soggy, roots are not able to gather water and nutrients. There are cases of plants wilting while surrounded by standing water. There was plenty of water, but the roots could not absorb it because they were starved for oxygen. Plants will stay healthier through the winter if the soil has good aeration and drainage.

Lawns may need to be aerated every year to every four years, depending on the soil and amount of foot traffic. The best kind of aerator cuts a plug of soil every few inches and drops it on the ground. Running a rotary mower over the lawn will shatter the plugs and return them to the soil. Then a thin layer of sand or Profile Soil Conditioner can be applied and raked into the lawn to fill the holes.

A Ross Root Feeder can be used to aerate around existing trees and shrubs. The best time to improve aeration and drainage for trees, shrubs, perennials and bulbs is at the time of planting. The planting hole should be three to five times the width of the root ball and about the same depth. Organic matter, such as compost, and sand or Soil Conditioner should be mixed into the soil. Plants that need extra drainage, such as Japanese maples, heather, tulips and daphne should be planted on a slope or a mound.

The only solution for areas that have standing water is to install a drain line. Three inch, perforated plastic drain pipe installed twelve to fifteen inches deep works very well. It can usually be hooked into the downspout drains if allowed by local building codes. Make sure that there is an even slope to the trench so mud doesn't clog up the low spots in the pipe.

Plants will tolerate the soggy soil better if they start the winter with a healthy root system. Root growth is encouraged by a fertilizer that includes phosphorus and potassium. In mid-fall, lawns should be fertilized with a fall and winter formula. A water soluble fertilizer, such as Peters 5-50-17, is good to use around trees and shrubs.

Freezing is the most common cause of winter damage. The damage is worse when plants thaw out rapidly. The best cold protection will raise the minimum temperatures and reduce rapid changes in temperature. A long cold spell will do more damage than one cold night. Cold weather that comes early or late in the winter will do more damage than cold weather in the middle of winter when plants are fully dormant.

Leaves and twigs are the first to be damaged by freezing. Many tropical plants cannot stand any frost at all. The plants that are native to the Portland area are hardy to at least 5 degrees. Some plants which are commonly grown in this area can be damaged by temperatures below 10 degrees. Many plants which are normally grown in California and shipped into the Northwest will be damaged by temperatures below 20 degrees. Winter temperatures in Portland dropped below 5 degrees in three of the winters during the 1980's, but have stayed above 14 degrees since then. It gets even colder at higher elevations. However, on clear nights with little wind, cold air drains downhill and collects in frost pockets where cold air gets trapped by fences and hedges. On these nights, the bottom of a hill might be ten degrees colder than the top of the hill.

Leaves and twigs can be protected by covering them with something. A cardboard box, garbage can or a bucket works very well on small plants. Larger plants can be wrapped in a bed sheet or in plastic. Clear plastic needs to be removed when the sun comes out so the plants don't overheat. Better products are Garden Blanket or Remay which breathe and can be left on as long as necessary. If it is windy, cover plants all the way to the ground.

Tree trunks sometimes develop sunscald, which is dead areas and cracked bark on the southwest side of the tree trunk. In freezing but sunny weather, the sun will warm up the trunk enough to begin growth. When the sun goes down, the soft bark tissues quickly freeze and die. Young trees, with few branches and thin bark are the most likely to get sunscald. Fruit trees, flowering cherries and plums, and maples are especially susceptible. The best protection is to wrap the trunk with tree wrap.

The roots of a plant are not as hardy as the top. Roots will often be damaged if the soil temperature reaches 20 to 25 degrees. Fortunately, moist soil is a fairly good insulator against cold. Water to keep the soil moist during freezing weather.

The roots of a plant in a pot or planter will be exposed to the cold much more than plants in the ground. Roots are mostly against the inside of the pot and plastic or clay pots offer no protection, although wood gives some protection. Planters should be moved to a protected place, such as an unheated garage or shed, or next to the house. If a planter is too heavy to move, it can be wrapped with bubble wrap.

Roots of plants in the ground may be protected with a layer of mulch such as straw, compost or bark dust. Mulch protects the roots from summer heat as well as winter cold. A layer of mulch one to three inches deep should be enough over the root zone, but the mulch should not be more than an inch deep around the trunk since it may encourage crown rot. The branches of low plants, such as azaleas, should be lifted out of the mulch. Mulch can be mounded over roses during short periods of freezing weather, then leveled again so the rose canes do not stay wet.

The best mulch for strawberries is Garden Blanket. It protects from the cold as well as straw and it can be left on in the spring to encourage an earlier harvest of berries. It can also be used on tomatoes and other vegetables to protect them from early frosts.

Winds also cause damage during in the winter, especially the strong, cold, dry winds that blow from the east. Shallow rooted trees are toppled much easier when the soil is soggy. Long branches are broken, especially if they are weighed down with snow and ice. Regular pruning to remove weak crotches and to keep trees compact will prevent breakage. Deep watering once a week in the summer encourages deeper root systems.

Wind chill increases the effects of the cold on evergreens. Wind can also dry out leaves quicker than plants can absorb moisture. This is called freeze burn and can happen to lawns as well as trees and shrubs. The best protection is to spray the leaves with Wilt Pruf. This product puts a natural coating on the leaves that seals in the moisture to prevent freeze burn. Plants such as daphne, rhododendrons and camellias in windy locations should be sprayed in late fall.

Be prepared. Start early to protect your plants from winter weather. Supply good aeration and drainage. Fertilize with a high phosphorus and potassium fertilizer. Wrap young trees with tree wrap. Apply a good layer of mulch. Spray tender leaves with Wilt Pruf. When freezing weather is predicted, move planters to a protected area, cover tender plants, and make sure the soil is well watered.


Search My Websites

Home Page
Site Map

Common and Scientific Names of Trees, Shrubs, Vines & Perennials
Spring Perennial Color
Summer Perennial Color
Fall Perennial Color
Winter and All Year Perennial Color
All Perennials in Alphabetical Order

Spring Shrub Color
Summer Shrub Color
Fall Shrub Color
Winter Shrub Color
All Year Shrubs
All Shrubs in Alphabetical Order

Spring Tree Color
Summer Tree Color
Fall Tree Color
Winter Tree Color
All Trees in Alphabetical Order

Spring and Summer Vine Color
Fall and Winter Vine Color and All Year Vines
All Vines in Alphabetical Order

More information can be found on my webpages:
Annuals, Biennials, Perennials and Bulbs
Edible Landscaping
Fall Planting
Fruit Tree Tips
Herbs for the Kitchen and Landscape
House Plants
Improving Soil
Lacebug Control
Landscape Design
Lawn Care
Oregon Invasive Plants
Oregon Native Landscape Plants
Pest Control
Plant Nutrients
Plant Propagation
Planting a Vegetable Garden
Planting in Clay Soil
Preferred Soil pH
Pruning for Shade, Flowers and Fruit
Remove Trees Roots and All
Rod's Garden Pruning
Roses
Seasonal Pruning Guide
Trees and Shrubs in the Landscape
Water Wise Gardening
Winter Plant Protection

Home Page
Site Map
No one wins an argument. Everyone wins a discussion.