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Hydrangeas brace for a heat slap — mulch deep, water early, look smug by Saturday.

Hydrangea care in Portland shifts into high gear this week as Tuesday's forecast climbs to 87°F before the weekend cools things back to the low 60s. That kind of whiplash stresses shallow rooted shrubs fast, especially mopheads and lacecaps just setting their first flower buds. Use the calm, dry stretch to mulch deeply, water with intention, and squeeze in any last spring shrub pruning you owe yourself.

This Week's Action List

  • Lay two to three inches of arborist chips or shredded leaf mulch around every hydrangea, keeping the mulch two inches away from the main stems to prevent crown rot. This is your single best defense against Tuesday's 87°F spike.
  • Deep water established hydrangeas with five to seven gallons per shrub early Tuesday morning before 9 a.m. — overhead sprinkling at midday will scorch leaves and waste half the water to evaporation.
  • Finish pruning any spring bloomers you missed in May (forsythia, weigela, mock orange, deutzia) by Wednesday. After mid June you start cutting off next year's flower buds, and that mistake haunts you for twelve months.
  • Adjust hydrangea color now while soil is workable: scratch in one tablespoon of aluminum sulfate per gallon of soil around the dripline for deeper blues, or garden lime for pinker tones. Portland's native acidic soil leans blue by default.
  • Scout dogwoods, lilacs, and ninebark for the first dusty patches of powdery mildew, especially on the shady west facing sides. Saturday's 63 percent rain chance plus cool nights is textbook mildew weather — improve airflow now by thinning crowded interior branches.

Frequently Asked Questions

When should I water hydrangeas in Portland during a heat wave?

Water deeply between 6 a.m. and 9 a.m. so foliage dries before the afternoon sun hits. Give established shrubs five to seven gallons at the base every two to three days during 85°F plus stretches, and skip overhead watering entirely to prevent leaf scorch and fungal issues.

Is it too late to prune spring blooming shrubs in Portland in June?

You have about one more week. Spring bloomers like lilac, forsythia, mock orange, and weigela set next year's flower buds on old wood starting in mid June, so any cuts after roughly June 10 will reduce next spring's bloom. Get it done by Wednesday if possible.