Most shrub problems on the Front Range are timing problems. The same pruning cut, watering or treatment produces very different outcomes depending on the month it happens in. This calendar follows the sequence GWTC arborists use for established landscape shrubs.
March–early April (early spring)
- Watch for bacterial blight after frost or wet weather.
- Avoid pruning when foliage is wet.
- Avoid overhead watering.
Late April–May (bloom period)
- Prune immediately after flowering — the most important timing of the year for spring-blooming shrubs.
- Begin scouting for borer activity.
- Do not delay pruning into summer.
Late May–June (early summer)
- Peak window for leafminer damage.
- Preventive borer treatments are only effective now, and only where there is a history of activity.
- Deep water during dry periods.
July–August (mid–late summer)
- Monitor for powdery mildew and leaf spot.
- Fungicides only if appearance matters — most of this is cosmetic.
- Avoid nitrogen fertilization.
- Avoid pruning; it removes next year's blooms.
September–October (fall)
- Rake and remove fallen leaves.
- Water before the ground freezes.
- Remove dead or broken branches only.
November–February (winter)
- Winter watering during dry, warm spells — every 4–6 weeks for evergreens.
- No pesticide treatments are effective in this window.
When to worry vs. when it's cosmetic
Act on entire stems dying back, blackened shoots and buds in early spring, repeated severe insect damage, and significant loss of vigor. Monitor — but don't treat — most leaf spotting, late-season mildew and minor cosmetic feeding damage.