Trees in a semi-arid climate
Boise's semi-arid climate means most landscape trees rely on irrigation through hot, dry summers; the record high is 111°F, and the National Weather Service notes that most precipitation falls from November through May. Winters bring around 20 inches of snow in an average year. Trees here need to handle drought, heat, snow and cold in the same year.
Watering through the dry months
Established trees need deep watering during summer, reaching out toward the drip line. Many Boise yards have pressurized irrigation for lawns, but shallow, frequent lawn watering doesn't always reach tree roots. Adding a deep-watering schedule for trees, or drip lines that run long enough to soak the root zone, helps. Mulch conserves moisture and moderates soil temperature.
Snow and ice on branches
Early fall snowstorms that arrive before trees drop their leaves can be especially damaging, because leaves catch more snow and add weight. Wet, heavy snow bends and breaks branches. Gently brush snow off small trees and shrubs, but don't shake heavily loaded limbs. Structural pruning, which reduces weak unions and long, heavy limbs, is the best long-term protection for large trees.
Freeze-thaw stress
NOAA's engineering weather data for Boise records about 78 freeze-thaw cycles a year. Thin-barked young trees can develop sunscald and frost cracks on their south and southwest sides in winter. Wrapping young trunks in fall and removing the wrap in spring helps some species. Watering trees deeply in fall before the ground freezes helps them go into winter well hydrated.
Winter pruning
Many trees are best pruned when dormant, and Boise's winters give a clear window. With leaves off, it's easier to see a tree's structure, find weak unions and deadwood, and make proper cuts.
Choosing the right tree
Selecting species adapted to the Treasure Valley's dry summers and cold winters reduces maintenance and water use. Ask a local arborist or nursery for recommendations, and plant with enough space from the house, sidewalks and overhead lines for the tree's mature size.
Before you hire
Ask Boise tree care contractors how they'll protect your yard and structures, whether they follow recognized pruning standards and avoid topping, whether a permit is required for street or protected trees, and for proof of insurance. Look up their Idaho registration with DOPL.
Roots, lawns and sprinklers
Many Boise yards combine large trees with lawns and pressurized irrigation. Trenching for sprinkler lines, fences or utilities can cut major roots, and heavy equipment can compact soil over the root zone. Before digging near a large tree, ask an arborist how close you can safely work. Damage done to roots often shows up in the canopy a year or two later, as thinning and dieback.
Storm cleanup
After a storm, broken branches hanging in a canopy, sometimes called hangers, can fall without warning. Keep people away from them and have them removed by a crew with the right equipment. Don't use a chainsaw from a ladder.