Fall Transition: Light, Not Cold, Is the Driver (Pacific Northwest 7b–9)

The Pacific Northwest doesn't run on the same clock as Zone 6. Mild fall temperatures mean cold isn't forcing your hand the way it forces mine in Kentucky. What's forcing the issue instead is day length and light intensity, both dropping fast through October regardless of how warm it stays.

Coastal OR/WA (8b–9): Caudex plants can stay outdoors longer than almost anywhere else in the country, but growth slows with the light regardless of temperature. Move seedlings and juvenile plants under supplemental lighting now rather than waiting for a cold snap that may not come this early.

Willamette/Puget lowlands (8a): Same light-deficiency pattern, with more overnight swing than the coast. Watch humidity closely in greenhouse and cold-frame setups — lower light plus high humidity is a damping-off risk for anything freshly sown.

Inland and higher elevation (7b): Closer to a true cold-climate transition. Treat it the way Zone 6 growers treat this window: watering pulled back, dormancy staged in over one to two weeks, and seed starting moved indoors under controlled heat and light rather than left to ambient greenhouse conditions.

Indoor and greenhouse strategy: If light is your limiting factor, don't try to compensate with heat alone — supplemental lighting on a 14–16 hour cycle does more for seedling development this time of year than raising ambient temperature does. Germination still runs best at a stable 85–90°F media temperature, which is where a dedicated heat-mat setup earns its keep regardless of how mild the room is.

What We're Growing With

• Desert Oasis Germination Media
• Adenium arabicum and obesum seed
• American Adenium Modular Germination System + Expansion Kits — provides consistent bottom heat to help maintain the 85–90°F germination target when used in an appropriate indoor setup

Full protocol: Seed Germination — Start to Transplant