Why Trees Come First in a Drought
A mature shade tree takes 20–30 years to grow. Your lawn can recover in a single season. If you're facing water restrictions and have to choose what gets watered, trees win every time — and it's not close.
Trees also provide measurable benefits that lawns don't: shade that reduces cooling costs, stormwater absorption, wind protection, and property value. Losing a mature tree to drought stress is an irreversible loss that no amount of reseeding can fix.
When and How to Water
Water on sunny days above 40°F. Choose mid-day so water soaks into the soil before evening temperatures drop and the ground refreezes. This applies to winter and early spring watering during drought — a situation the Front Range is squarely in right now.
Focus on the drip line, not the trunk. A tree's root system extends roughly to the outer edge of its canopy — the drip line. That's where feeder roots absorb water. Watering at the trunk base does little good. Set up a soaker hose or move a sprinkler head in a ring around the outer canopy footprint.
How much water: Two common rules of thumb work well:
Boulder's city forester recommends replicating 1 inch of rainfall over the root zone. Measure this by placing small containers (tuna cans work) under the irrigation area and running water until 1 inch accumulates.
An alternative method: apply 15 gallons per inch of trunk diameter. A tree with a 4-inch trunk gets 60 gallons. A tree with an 8-inch trunk gets 120 gallons. Use a hose at a slow trickle and time how long it takes to fill a 5-gallon bucket — then multiply.
Deep watering is better than frequent shallow watering. A slow, deep soak encourages roots to grow deeper into the soil profile, making the tree more resilient for future dry periods. Shallow, frequent watering keeps roots near the surface where they're most vulnerable.
Frequency: Once or twice a month during dry winter and spring periods. In summer under drought restrictions, water as often as your restriction stage allows, prioritizing trees over lawn zones.
Mulch — But Do It Right
Apply 2–3 inches of wood mulch in a ring around the tree, extending as far out toward the drip line as practical. Mulch retains soil moisture, moderates soil temperature, and reduces competition from grass and weeds.
Keep mulch 1–2 inches away from the trunk. Mulch piled against bark ("volcano mulching") traps moisture against the trunk, promotes rot, and creates habitat for boring insects. Pull it back to leave a visible gap around the base.
Signs of Drought Stress
Wilting or curling leaves during the growing season, especially when temperatures are moderate, indicate the tree can't pull enough water from the soil.
Leaf scorch — brown, crispy edges on leaves — shows up when transpiration demand exceeds water availability. Common on maples, lindens, and other broadleaf species during Front Range summers.
Premature leaf drop in July or August means the tree is shedding leaves to reduce water loss. It's a survival mechanism, but repeated years of early leaf drop weaken the tree.
Bark cracking or splitting can result from the rapid temperature swings that Colorado's dry climate produces, especially on south- and west-facing trunk surfaces.
Don't Forget Evergreens
Evergreens are especially vulnerable to winter drought on the Front Range. They continue transpiring (losing water through needles) all winter, but frozen or dry soil can't replace what's lost. Chinook winds — the warm, dry downslope winds that hit the foothills — accelerate this desiccation dramatically.
Signs of winter desiccation include browning needle tips, especially on the south and west sides of the tree. Water evergreens on warm days throughout winter, focusing on the drip line just like deciduous trees.
Consider drip irrigation or a soaker hose around the drip line as the most efficient watering method — it minimizes evaporation and delivers water directly to the root zone.