January 1, 2016

Will our unseasonably warm winter damage our plants?

Mayflowers for Christmas? It happened this December, but it with this plant, Epigaea repens, it's not completely unheard of - it's just rare. Records show that this has occurred in the past, in particular, in 1776 here in Massachusetts, where the Mayflower is our State wildflower. but what about all of our other plants, trees and shrubs that are blooming during this mild, record-breaking winter?

Here in the Northeastern United States, we are experiencing an unseasonably warm winter, so 'unseasonable', that it's breaking all time records here in Massachusetts. Blame it on El Niño, global warming or just a freak of nature, the truth is, plants are blooming and many gardeners are worried about damage.

Hamamelis x intermedia 'Arnold's Promise' is variable, blooming early in February during mild winters, but as late as April, after a harsh winter, as we had last year. Never have I seen it bloom outdoors during December, but I suspect that it isn't that unusual, as this is truly a vernal plant, able to burst into bloom after a few days of mild temperatures. I can usually force branches into full bloom in just a week, during mid-January. So I am not worried.

Many of us are worried about our cherry trees which are blooming in December, or our daffodils, spirea or witch hazels which are coming into full bloom many months earlier than their normal blooming time. I too am worried, for in my garden, many shrubs are beginning to open their flowers, particularly those which normally would bloom in late March or April. But I am noticing something - all of the plants which re blooming now are not native. They are all imported species either from Asia or Europe. While our native species may be able to handle this climate shifts, most of the damage seems to affect our ornamentals, most of which come from lands where winter behaves differently than in the already variable climate of the North Eastern US.

We know all too well about this fact. An alpine plant from the high alpine mountain tops in the alps can perish in our coastal Boston gardens, since they are used to a steady, certain period of thawing at snowmelt, never to freeze again until autumn, whilst in the New England garden, said alpine may thaw and refreeze multiple times during the average winter or spring.

We all love winter-blooming hellebores, but this Helleborus niger, purchased as a florist plant for the Holidays, usually fails in our New England garden. I have been able to have some come back for a second or third year, usually blooming during a mild winter around New Years Day, the species usually fails after a hard winter, since it wants to bloom very early, January or February. Rock hard Hard re-freezes are devastating, tearing new roots and destroying the crown.

If you garden in the North East, you know about this sudden death syndrome.  It is not uncommon at all for perennials to emerge at snowmelt, grow a bit with new tender during a mild April or May, only to refreeze, thus tearing their roots, and causing irreparable cellular damage resulting in certain death.

We loose many plants to this pattern of freeze, thaw, refreeze here in the Northern Atlantic states. The Sadly 'perfect spring' rarely occurs. Ironically, last year, we did have the 'perfect spring'. Long, slow and cool, with no killing refreeze. I guess we are paying for this anomaly now with the warmest December in recorded history.

An un identified shrub in the perennial border clearly emerging early, on Christmas day. With no dormant buds to back up this emergence, I fear this shrub may not survive.

Warmer than average winters are not that unusual here in New England, but only rarely have they been truly damaging. Most severe cases are measured through how they affect agricultural crops, most recently, in 2012 when 90 percent of the apple crop was damaged in the northeaster US due to a single freeze in April, and in 1934 more than 3/4's of the apple trees in the Northeast were killed by a warmer than normal winter, which then followed with a cold snap.  I have a photo of our house featured in our local paper in 1934 with the apple trees in bloom during January. This record breaking winter of 1934 was reportedly caused by many of the same factors that caused the infamous dust bowl in the Western US a few years earlier. My father remembers when it 'snowed red' that winter, with snow stained by airborne dust. Many of the Baldwin apple trees were lost in New England during that winter.

Not a good sign at all, for this Spirea thunbergii 'Ogon'. Native to China and Japan, it's not unusual for for this shrub to hold onto it's leaves until late November, it is unusual for it to be emerging into new growth at every bud on New Years Day. Typically an 'early emerger', this full-on burst of new growth before the harshest of winter arrives, may not ensure it's survival in the garden come spring.

Native plants usually survive such periods of warm weather, but this winter is not over yet, and I do wonder how the mild temperatures this year will change our native plants. I mean, 20, 30 or even 100 years of record keeping isn't long when it comes to climate change. But we are breaking 300 year records, still small perhaps, but I do begin to worry when I see things like multiple records being broken in just ten years. In 1995 we experienced a late frost which killed many of our native oaks and ash trees - I remember this damage, since Christopher Lloyd was visiting here, speaking at Tower Hill Botanic Garden during that freeze in May. Cold snaps and odd late freezes are one thing, but warm winters that cause entire populations of native trees to bloom off season is another. Let's hope this only affects our imported species.

Even in the greenhouse, plants are early. This camellia is mimicking what is happening in North Carolina right now - blooming before New Years Day. Still, it's an early blooming variety from Japan which usually starts for us around Christmas Day.

So whether this year's mild weather is the result of long-tern climate changes or not, we all know that there are some troubling signs in our own gardens. Personally, I am thrilled that my heating bill for the greenhouse has been practically nil so far, but those gains may be offset by plant loss around my garden. Facebook abounds with images of freaky, blooming things out-of-season.

Buds, such as these on Rhododendron x narcissiflora are emerging, or at least, swelling. I am not certain if they are tender enough to cause damage, but given that one of the parents of this cross is R. luteum from Europe, it may be confused and beginning to emerge from dormancy? It's demise may be best, since we keep honeybees, and the nectar of  R. luteum contains grayanotoxin - toxic honey is never good for human consumption.

To those who keep records about such things, it's all more than alarming. Climatologists know the numbers.  If we kept records in our own gardens, we might, and should be alarmed as well. Even short term. Lilacs are blooming on average, four days earlier than they did in the 1960's, according to David Wolfe, a Cornell Department of Horticulture professor who pointed out in a 2007 article that cultivated crops such as grapes and apples are blooming on average, six to eight days earlier now than just thirty years ago. Mr. Wolff focuses on how climate change is affecting agriculture, where many crops are migrating northward in an effort to improve growing conditions. It doesn't matter if you believe in climate change or not, it's happening either way.

There are some helpful resources for you to not only follow, but to participate with. Project Budburst allows you to enter information about what is happening in your own backyard and garden plus offers lots of other features. It's sponsored by he National Science Foundation. Some of the reports on Project Budburst reinforces my thoughts about how our native plants are able to handle such mild winters as we are experiencing this year.

Many Daphne species bloom through the winter, but typically, not here in Zone 5. This Daphne transatlantic has bloomed during all 12 months, when it is mild, but it's also not native to North America. Flower buds remain closed until temperatures are mild, when they open.

This year has been more challenging for forecasters though, even though we were being told that this epic El Niño was over due. Besides, the West needed rain, the mountains are grateful for the snow, as are the skiers in Colorado and Utah. Here in the Northeast, forecasting how this winter may layout has been more challenging, even though scientists have learned so much recently. There are other factors beyond El Niño which complicate things.A cold, deeply frozen winter in Siberia can affect the Jet Stream in Canada and Northern North America. Arctic Oscillation can mean a colder and snowier winter in the North East, but this year is more complicated, since we are experiencing both a snowy, cold arctic Siberian winter and a strong El Niño. How it will play out remains to be seen.

In my garden, I am noticing that the plants which are emerging early are mostly Asian species. Native plants seem to be better with dealing with warm autumns and unseasonable weather like this. I feel that this autumn started off with a bad sign - and earlier and harder frost than what was considered normal occurred in early October. Frost, temperatures just below freezing usually triggers a chemical reaction in the petioles of leaves on trees, blocking chlorophyll from being produced, leaving behind other chemical pigments which provide our bright, colorful autumn foliage of reds, orange and yellow here in New England.

Our earlier than normal deep freeze, was so cold (below 24 deg. F) froze the leaves and killed them in their green state, before they had a change to slowly progress to a colorful state. Most remained on the trees until they faded into a pale olive brown, and then finally fell. Asian trees, such as Japanese Maples, Himalayan Birches and Stewartia kept their brown, dried foliage until late November, the petioles unable to release their leaves without the proper maturity. Many berried shrubs such as the bright violet berries on callicarpa were so damaged that they rotted on the branches, while the foliage, which typically would turn yellow and drop after a light frost, simply remain on the branches in their damaged, brown state. Many are still holding onto their leaves.

After that initial hard freeze in early October, the temperatures in Massachusetts have remain mild since early October, only now, this week around the New Year, dropping again to 18-20 degrees. December 2015 was the hottest in recorded history, with every day averaging about average. The plants, in particular, the Asian species are not handling the mild weather well. Most are beginning to sprout, with buds which should be dormant, emerging on Stewartia, Deutzia, Spirea and Hamamelis.

Not all is doom and gloom however, since most native species seem to have remained dormant in our gardens, but the jury is still our with our imported plants species. Sadly, most of our garden plants today are not native, (perhaps the best reason of all for using more native plants in our landscape?) Non natives, be they lilacs, Spirea, apples, Japanese Maples, hydrangeas even the newly available lace-leaved elderberries with purple or golden foliage, can be damaged or killed.

A purple lace-leaf Elderberry, so stylish in the garden may be emerging too early. This European native is showing elongated growth during late December, which is never a good thing in our zone 5 Massachusetts garden. Although temperatures have hovered near 60 degrees for most of the month, we are forecast to get 18 deg. F next week. I fear that I may loose this import, while our native elderberry plants remain dormant.

 Elderberries are particularly susceptible to warmer than average winters since they form their dormant buds earlier in the late summer, and they are not used to our uncertain winter temperatures, which may spend a few weeks near 70 degrees F, then drop to a frigid, killing 10 degrees overnight, only to rise again to a balmy 65 degrees.

Some elderberry buds like these, may remain dormant through this winter, but my fingers are crossed.

Most at risk are those perennials which typically emerge at snow melt. We have enough problems with them in the spring, when an early emergence followed by a hard freeze kills many of our beloved garden perennials, but even in January, an early emerging Helleborus nigra can face death with a hard, colder than average winter, without snow cover. I expect to looks many plants this year, in particular some Spirea and Elderberries which have been motivated to emerge 5 months early.

Native plants respond to day length more than they do temperature, so most of our wild plants will be safe, but we should keep our fingers crossed that Asian agricultural crops such as apples, pears and cherries do not bloom before truly cold weather arrives, or we risk loosing much more than some garden flowers.


  1. For what it's worth, I have had good luck with those HGC Hellebores when I get them in the spring as young plants, and they have a whole growing season to settle in. The one time I bought one in the grocery store as a seasonal potted plant, it couldn't handle the onslaught of winter. Usually my H. nigers form buds before snow's arrival and bloom in very late winter/very early spring (ie, mud season). The freeze/thaw of this time doesn't seem to bother them. This year I actually saw blooms on my Christmas rose on Christmas.

    1. I almost mentioned that, Kathy. Like many plants such as heathers, those set out early in the spring survive much better since they are able to establish root systems. One problem we have here is the freeze thaw cycle, but that may be because we are 30 miles from the ocean. I have been able to keep them for 5 years or so, but they only bloom early (Jan-Feb) during mild winters.

  2. Oh, and I meant to ask--are you growing that Mayflower in your garden, or did you photograph it in a wild place?

    1. Growing it in the garden. Stock came from a pink selection from Maria at Mont Echo years ago. The one flat she left with us has spread into a large colony under the white pines. I imagine that our native plants are blooming on the ledge in the woods though, I've seen them bloom in January thaws in the past.

  3. Here the weather is cool for a winter, the camelia began flowers ,Happy Year,
    Best regard from Belgium.

  4. :: Native plants respond to day length more than they do temperature ::

    Could you provide a source to explore this a little further? I haven't heard that before. I know there are differences among plants; some hostas are clearly day-length-sensitive (though not native; most Asian). On the sheltered east side of the house, the Ozark or spring witch hazel (Hamamelis vernalis) bloomed strongly right along with the earliest hellebores during the freaky warmth of December; maybe that doesn't count as a counterexample since it's not actually native here in western Virginia, though.


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