Denver's high-altitude, semi-arid climate (Zone 5b/6a) with intense UV, dramatic temperature swings, and 100+ freeze-thaw cycles demands proactive fall preparation. Proper winterization protects plant investments, prevents costly damage, and ensures vigorous spring emergence.
Lawn Winterization
- Fertilize: Early Sept (1 lb N) + late Oct (1 lb N winterizer) — potassium for cold hardiness
- Aerate: Sept–early Oct — relieves compaction, improves water infiltration
- Overseed: Thin areas with tall fescue blend — establishes before winter
- Sod: Early fall only; keep moist 7–10 days; avoid heat waves
- Mow: Gradually lower to 2.5–3" final cut; mulch leaves
- Water: Monthly winter watering (Dec–Mar) if no snow cover — critical for root survival
Tree and Shrub Care
Pruning
- Timing: After leaf drop (dormant) — Nov–Feb
- Spring bloomers (lilac, forsythia): Prune AFTER flowering
- Summer bloomers (spirea, potentilla): Prune dormant season
- Technique: ¼" above bud at 45°; no flush cuts; no paint
- Hire ISA Arborist for: Large trees, structural pruning, near utilities
Winter Protection
- Burlap screen: Broadleaf evergreens (boxwood, rhododendron), young trees — wind/sun protection
- Anti-desiccant: Wilt-Pruf on broadleaf evergreens (Nov, Jan)
- Mulch: 3–4" wood chips to drip line; pull 3" from trunk
- Tree wrap: Thin-barked young trees (maple, linden) — Nov–Apr; prevent sunscald/frost crack
- Deer protection: Fencing, repellents — critical in metro Denver
Watering
- Deep soak: Late Nov (before ground freeze) — 10–15 gal/inch trunk diameter
- Monthly winter watering: Dec–Mar when >40°F, no snow — same volume
- Evergreens: Higher priority — transpire all winter
Perennial and Bulb Care
- Cut back: After hard freeze — leave 2–3" for crown protection (except evergreen perennials)
- Mulch: 2–3" after ground freezes — prevents heaving
- Spring bulbs: Plant Sept–Oct (tulips, daffodils, crocus) — 3× bulb depth
- Tender bulbs: Dig dahlias, cannas, gladiolus — store 40–50°F
Hardscape and Feature Winterization
Irrigation
- Blow out: Compressed air (50–80 PSI) — all zones, backflow, mainline
- Timing: Before first hard freeze (typically Oct–Nov)
- Professional recommended: Proper volume/pressure prevents pipe damage
Water Features
- Ponds: De-icer/aerator for gas exchange; remove pumps; net leaves
- Fountains: Drain, cover, store pump indoors
- Pondless: Drain basin; cover
Outdoor Living
- Furniture: Cover or store; clean first
- Grills/kitchens: Cover; disconnect gas; winterize plumbing
- Pavers/concrete: Seal if due; ensure drainage; no de-icing salt
- Lighting: Check fixtures; LED handles cold better
Pools and Spas
- Pool: Professional closing — chemistry, cover, equipment winterization
- Spa: Maintain heat or full winterize; strong cover for snow load
Tool and Equipment Care
- Clean, sharpen, oil tools
- Stabilize fuel or drain mowers
- Store batteries 40–60°F, 40–60% charge
- Service equipment off-season
For Denver landscaping resources, visit mylandscaper.biz. Disclaimer: Educational. Adjust timing for microclimate and elevation.
