I'm still learning about deciduous azalea. I really don't have much to add beyond what I said in the 2019 thread here;
I have admired deciduous azalea for years. Their growth pattern of short then long internodes is very different from the Satsuki and Kurume. I am particularly interested in the 'Northern Lights' series of winter hardy azalea hybrids. Please post your experiences here. What works, what...
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I did learn that while the stems, branches and flower buds are winter hardy to -20 F, or -28 C, the roots need to be healed into the ground. Pots set on the ground apparently got to cold, and roots died. The plant flowered, flowers wilted fast, then died without making leaves. That suggested roots had been winter killed. We did have a week of -17 F, or - 26.5 C at night. So we know that was too cold. I suspect healed in the ground would have kept the roots at or above 0 F or -18 C. Soil is a good insulator, heat from the earth does keep the ground warmer than the air temp, and damps out rapid day-night fluctuations. I have not emptied the well house yet, where my surviving deciduous azalea is being stores. I'll chime in when I have more to report.