Cold Damage to Plants: Protection Strategies and Frost Date Averages

Originally written March 2002; details accurate for any winter.

Last night WEATHER.COM predicted 19°F at 6:00 a.m. Saturday; now 26°F. For Cumming 24°F, Jonesboro 27°F.

Questions: Will this hurt plants? Should I cover them? Which ones and how?

After February 28 freeze, many plants in full bloom had flower damage. Deciduous magnolias, early azaleas, early daffodils had brown blooms. Bradford pear flowers less noticeable, probably cold-related.

Plants blooming on last year's buds can lose flowering capacity if buds damaged before flowering. Bigleaf hydrangeas: mine have 2+ inches green growth from stems. Green tip buds form May/June blooms. I don't want to lose blue hydrangea blooms!

I have a big hydrangea bed and azaleas 75% in bloom. I'll cover three beds with black plastic from Home Depot, compare to uncovered beds. 26°F seems cold; I can raise temperature under plastic a few degrees by anchoring with stones and limbs.

Later-blooming azaleas (satsukis) and those with tight buds should bloom normally. Hydrangeas with frozen tip buds may still have lower buds producing flowers later (June/July/August vs May/June). Watch predicted lows in your area and plan accordingly!

PREDICTING FIRST & LAST FROST

Predicting first frost is tricky. Average first frost: November 13. Earliest: October 25. Latest fall frost: December 6.

SEVERE COLD

Using 16°F as severe cold mark: 90% chance occurrence before Dec 25 yearly. Spring average: February 5. Latest 16°F in 30 years: March 4.

SNEAK PREVIEW FOR SPRING

Using 32°F reference: most likely last frost March 27. Earliest: February 16. Latest spring frost: April 23. In 1983 last frost April 20 (imagine what freezes did to spring landscapes!).