Weston Logo

Memorial Day Update – All locations will be OPEN on Monday, May 27th normal business hours!

Cold Hardiness

Cold Hardiness


By R. Wayne Mezitt

Surprising as it may seem, the recent period of extended cold temperatures we’ve been through may actually be beneficial for our full enjoyment of flowers next spring. As challenging as we may perceive winter has been, all the weather we’ve experienced still falls pretty much within the expected “normal” range for this region. Plants are affected by absolute temperatures; they can become dehydrated by winds, but plants do not experience the “wind-chill-factor” we see so often on the weather reports.

How well the trees, shrubs and plants in our landscapes tolerate winter is affected by their winter hardiness physiology. Plant cold-hardiness differs among individual plants; it is determined genetically for each variety and cultivar. Most landscape plants used in this region are well adapted to tolerating cold temperatures within their hardiness rating. Referring to the USDA Hardiness Zone Map (below), our region is in Zone 6A where average annual extreme minimum temperatures are minus 10°F to minus 5°F.

Researchers tell us that each winter plants develop their optimum tolerance for cold temperatures with gradual acclimation. “Cold hardiness requires that the plants have acclimated properly through the natural process of lengthening nights and cool temperatures to become dormant. This is an active metabolic process requiring adequate moisture and proper nutritional balance.”[1] With the welcome rainfall last November and the normal progression into winter weather we went through in December, these weather conditions have been met.

Flower buds are generally less cold-hardy than growth buds on the same plant. The actual flower bud hardiness of each individual plant is determined by “the relationship between the degree of cold hardiness (supercooling ability of florets) and the acclimation intensity in flower buds.”[2] Buds are at their most-hardy condition when full dormancy conditions have been reached.

Since Christmas Day, recorded maximum temperature for the Hopkinton area never rose to freezing (that’s <32°F continuously for more than 2 weeks), and in that period, seven consecutive days recorded a maximum temperature below 20°F. The minimum recorded temperature briefly touched minus 13°F on January 2, only slightly below what’s considered normal for our Zone 6A hardiness rating. Leading up to this extended cold period was a gradual cooling period, so no sudden temperature changes occurred.

Based upon all of this, it’s reasonable to conclude that winter is progressing normally, plants have properly acclimated for their full winter hardiness and should perform normally in spring. The rhododendron flower buds I tested today for winter damage are still fully viable. Of course how each plant actually turns out depends upon other factors where it is growing, as well as what winter will be bringing going forward.

[1] Sally Perkins, The Rosebay Volume XXVI Spring 1999 official journal of the American Rhododendron Society Massachusetts Chapter, https://www.rosebay.org/chapterweb/rosebay/what_is_hardiness.html
[2] ibid

Share Via:


Weston Nurseries is committed to being a center for horticultural knowledge. Enjoy!

Generic selectors
Exact matches only
Search in title
Search in content
Post Type Selectors
Search in posts
Search in pages

Shops Trees, Shrubs, & Perennials – in stores and online.


Online Shopping at Weston Nurseries

We are excited to offer two unique opportunities to shop online at Weston Nurseries.

Farm To Door™

WN Online Shopping icons_Ship to Door
Plants shipped directly to you!

Browse our online inventory for a huge selection of plants available to ship directly from the farm to your home! Anywhere in New England!*

Shop Our Garden Centers

WN Online Shopping icons-02
Great for large plants and larger orders!

Shop your local store for plants, garden supplies, soil, mulch and more. Then pick up your order at the garden center or arrange for local drop off!

If you are interested in ordering gift cards, please click here!
*Some restrictions may apply to certain states.


Memorial Day Weekend Flash Sale On Hydrangeas!

25% off all Hydrangeas this weekend only!

Saturday, May 25th – Monday, May 27th! 

Hydrangeas are a classic and beautiful sign of summer. Celebrate Memorial Day Weekend by sprucing up your yard with some new hydrangeas. Discount applies at all locations.

*Sale Fine Print:

For “Cash and Carry” transactions only. Offer good while supplies last.

No open orders or deliveries for future dates. All Flash Sale products must be taken the same day. Not valid on previous orders. No transfers allowed between stores on any sale items.

Skip to content