Protecting Shrubs and Trees in Winter

Tree wrapped in winter to protect bark of plant

How to Help Your Landscape Plants Survive Boise’s Often Cold, Dry Winters

Quick Facts

Boise’s high-desert climate can be tough on shrubs and trees during the winter months.Cold temperatures, dry winds, and fluctuating freeze–thaw cycles can all damage plants if they aren’t protected properly.

Common winter threats:

• Sun, wind, and cold: can dry out evergreen foliage, damage bark, and kill buds or branches.

• Snow and ice: can bend or break branches.

• De-icing salts: used on roads and sidewalks can harm roots and foliage.

• Wildlife: deer, rabbits, and rodents often feed on bark and twigs when food is scarce.

 Cold Damage

Causes of winter injury:

• Planting species not always hardy enough for Boise’s USDA Zone 6b climate.

• Extended cold snaps or drying winds that dehydrate plant tissues.

• Sudden temperature swings and lack of consistent snow cover.

• Dry soil conditions in late fall that increase susceptibility to cold.

Prevention:

• Choose trees and shrubs rated for your zone (at least Zone 6 – the lower the number, the more cold hardy the plant is).

• Water deeply in late fall before the ground freezes (usually around the 15^th of October).

• Apply a 3 to 4 inch layer of mulch around the base to insulate roots and conserve moisture.

• Avoid pruning or fertilizing in late summer to prevent tender new growth that’s easily damaged. (Pruning after the foliage drops off and before hard freezes takes place is ideal. We recommend fertilizing around the 15^th of October and as late as the 3^rd week of November, as long as there is no snow on the ground).

  
  

 Root Injury

Roots are often less cold-hardy than the rest of the plant. In Boise’s coldest winters, unprotected roots can be damaged when soil temperatures drop near freezing.

Soil temperature is influenced by:

• Moisture: damp soil holds heat better than dry soil.

• Mulch and snow cover: help insulate the soil.

• Planting holes: gaps or cracks in new plantings allow cold air to reach the root zone.

How to protect roots:

• Cover the root area with 3–4 inches of wood mulch, keeping mulch approximately 6 inches away from the trunk.

• Water well before the first deep freeze.

• Fill any cracks around new plantings to prevent cold air from seeping in.

  
  

 Frost Heaving

Boise’s frequent freeze–thaw cycles can cause the soil to expand and contract, pushing plants out of the ground and damaging roots.

Prevention:

• Maintain a 4 to 6 inch layer of mulch to keep soil temperatures steady.

• Check plants in early spring and re-firm any that have been heaved out of the soil.

  
  

 Winter Injury on Trees and Shrubs

• Deciduous trees: may develop bark cracks or sunscald, especially on south- and west-facing trunks.

  • Wrap young or thin-barked trees with tree wrap or burlap from November through March. (be certain to unwrap trees around March 15^th).

• Evergreens: can suffer from winter burn when moisture loss exceeds water uptake.

  • Water thoroughly before the ground freezes and during mild winter spells if soil isn’t frozen.

  • Use windbreaks to protect broadleaf evergreens from harsh winds when possible. Conifer shrubs and trees do not need protection in most cases. If you’re not sure about what plants need protection, we have an Idaho Certified Nurseryman on staff to help you with all your gardening questions.

    
    

 Animal Damage

Deer, rabbits, moles, gophers, and voles are some of the animals that  can cause significant winter damage by feeding on roots, bark, buds, and twigs.

Protection tips:

• Wrap trunks with tree wrap, plastic tree guards or hardware cloth.

• Install fencing (6 to 8 feet tall for deer) around vulnerable plants if deer is a problem in your area of Boise.

• Keep grass trimmed and remove brush piles where rodents hide.

• Use repellents or scent deterrents during peak browsing periods.

  
  

 Final Tips

Boise’s winters are unpredictable—some years mild, others sharply cold and dry. Preparing your landscape each fall with deep watering, proper mulching, and wildlife protection helps ensure your trees and shrubs emerge healthy in spring.