Hardening off dinnerplate dahlias
It's me again! Thinking about hardening off my dahlias, and wanted to know what night time temperature is optimal. I can cover them with a sheet overnight, and they would be on my west facing patio beside a south facing wall... Thanks for all your help! Great service! /sorry for the typos.
Larimer County Colorado flowers: annuals and herbaceous perennials
Treat them as a warm season annual, with nighttime temperatures are consistently above 55 degrees F. In general, the safest approach would be to not let them stay outdoors until the end of May or early June. You can harden them off a couple weeks before, by only bringing them outside on warm, sunny days and keeping them indoors at night.
To harden them off:
Harden your plants off gradually, over a 7-10 day period. Ideally, start the process on a mild or cloudy day. Place plants outside in a shaded location for 2-3 hours, sheltering them from strong wind. Move the plants back inside at the end of this time.
Each day, gradually increase your plant's time outside and their sun exposure by a few additional hours. At the same time, gradually reduce how often you water then, but don't allow the transplants to wilt. After several days of 10 to 12 hours outside, leaved the plants outside for 24 hours a day for a couple days. At this point, your plants are ready for transplanting.