Heat dome incoming — water deep, shade the lettuces, and don't trust Sunday's 98°F.
I've been bracing my mid June Portland garden for heat all week, and Sunday's forecast of 98°F just confirmed it — this is the first real heat dome of 2026. The week starts mild and damp, then climbs hard from Thursday on, which gives us a tight three day window to deep water, mulch, and rig shade before things get ugly. I'm treating Wednesday as my prep day and Saturday evening as the last chance to baby anything tender.
This Week's Action List
- Deep soak every bed Wednesday or Thursday morning before the heat lands — I run my drip lines 45 to 60 minutes per zone so water reaches six inches down, where roots will retreat when surface soil bakes Sunday.
- Throw 30 to 50 percent shade cloth over lettuce, spinach, cilantro, and any newly transplanted starts by Friday afternoon. I clip mine to hoops about 18 inches above the canopy so air still moves; without it, my lettuce bolts to flowers by Monday.
- Mulch any bare soil to a full three inches this week using straw, leaf mold, or arborist chips — every square foot of exposed dirt is a heat sink that cooks shallow tomato and pepper roots when air temps top 90°F.
- Scout for spider mites every morning Thursday through Sunday, especially on beans, cucumbers, and tomatoes against south facing walls. I flip leaves and look for fine webbing and bronze stippling; a hard spray of water under the leaves at dawn knocks early populations back before they explode.
- Harvest peas, lettuce, cilantro, and any cool season greens by Thursday morning — anything left in the bed through Sunday's 98°F will turn bitter or bolt overnight. I'm pulling my entire spring pea row Friday and replacing it with bush beans the following week.
Frequently Asked Questions
How do I protect my Portland vegetable garden from a 98°F heat dome?
Deep water two days before the peak, mulch every bare patch to three inches, and rig 30 to 50 percent shade cloth over leafy greens and recent transplants. Skip midday watering, which scorches leaves; instead soak deeply at sunrise so roots are charged before the worst heat hits between 2 and 6 p.m.
Should I fertilize my Portland garden during a June heat wave?
Hold off until temperatures drop back into the 70s and 80s, usually by midweek after the spike. Fertilizing stressed plants in 95°F plus weather pushes weak growth that wilts fast and attracts aphids and mites. I wait until I see new growth resume on tomatoes and peppers, then resume my normal fish emulsion routine every two weeks.