✨ Tall spires, taller stakes — delphiniums riding a 94°F spike into a soggy weekend.
Delphinium care in Portland gets interesting this week, with a 94°F Tuesday slamming into a 61°F rainy Saturday and stems that can snap in either extreme. I'm out at dawn tying up my Pacific Giants before gravity hits them sideways, then bracing for the weekend gusts that always seem to arrive right when the lower florets open. If you grow these blue spires anywhere east of the West Hills, this is the week the whole season is won or lost.
This Week's Action List
- 1
Stake every spire taller than two feet now. I use 5 foot bamboo canes set 3 inches from the crown and tied loosely with soft jute every 12 inches — figure eight knots, never tight loops, because stems thicken fast in heat.
- 2
Water deeply Monday and Tuesday before the 94°F spike: 2 gallons per established clump, delivered to the soil at the base, never overhead. Delphiniums wilt dramatically above 90°F even when soil is moist, so a thick 3 inch mulch ring of fine bark keeps roots near 65°F.
- 3
Throw 30 percent shade cloth over east facing delphinium beds from noon to 5 PM on Tuesday. I clip mine to tomato cages set behind the plants — it knocks the leaf scorch risk way down without flattening bloom color.
- 4
After the rainy Friday and Saturday, walk the border Sunday morning and snap off any spires that flopped past 45 degrees. Cut the stem just above a strong side bud and you'll often get a second flush of smaller laterals in August.
- 5
Feed lightly this week with a balanced liquid fertilizer at half strength — something like a 5 to 5 to 5 fish and kelp blend. Skip high nitrogen now; it produces soft growth that collapses in the next heat wave, and Portland always has a next heat wave.
Frequently Asked Questions
Why are my Portland delphiniums wilting even though the soil is wet?
Delphiniums are cool climate plants and shut their stomata when air temps climb past 90°F, so the leaves droop regardless of soil moisture. I treat it as a sun and air problem, not a water problem — afternoon shade cloth and a deep mulch layer help far more than another round of irrigation. They usually perk back up by 8 PM once temperatures drop below 80°F.
Will delphiniums rebloom in Portland if I cut them back?
Yes, and Zone 8b's long season makes it worth the effort. Once the main spire finishes, I cut the whole stalk down to the basal foliage and side feed with compost — about half the clumps in my garden throw a second, shorter flush in late August or early September. Keep them watered through the dry stretch and they'll deliver.