Well, we know we’re not alone, but here in southern New England, we’ve had an exceptionally hot dry summer. The amount of precipitation in our area has varied due to isolated showers, but I would guess here at Avant Gardens we have totaled less than 1 inch during the past 75 days. Lack of rainfall plus high humidity, coupled with daily temperatures in the high 80s and 90‘s can have an effect on plants. (Many plants begin to suffer physiological damage when temperatures remain above 86F or 30C)
This brings up the classification of plants rated for Summer Hardiness. The American Horticultural Society (AHS) has created a Summer Heat Zone map of the US. Regions having less than 1 day with temperatures above 86F (30C) are classified as zone 1, and on the other end of the spectrum, the areas having the most days with high temperatures are classified as zone 12. This may correlate with the familiar USDA Winter Hardiness Zone Map (which rates average lowest temperatures) but in some cases it does not. Folks in the southern US have learned that Summer Heat Zone Hardiness is definitely a criteria when selecting plants. The above map will need regular adjustments now that global warming is causing extreme temperatures worldwide, and northern gardeners will have to pay heed to which plants will survive/perform with higher summer temperatures.
We’ll be ruling out more plants that do well in our gardens in the future, I’m afraid, as climate change continues to affect what we can and cannot happily grow.
Have you come to the conclusion that some plants, which once thrived in your gardens, no longer will? Which plants have you found best withstand our ever warmer drier summers?