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How this mild winter is affecting your plants

Posted by David Epstein  February 8, 2012 02:35 PM

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One of the questions I am getting asked quite a bit the past month is how will the lack of snow and cold affect the plants? I know many of you have noticed all sorts of strange behavior with the flora. I have seen bulbs coming up since January, rhododendron opening, forsythia in bloom and even roses that still have not lost their leaves. There are reports of magnolia in flower in Boston and the south shore. All over the northeast we can see the effect the mild winter is having on plant life.

Lets start with the bulbs. Bulbs will grow in response to two variables, light and temperature. The light is a predictable factor in that daylight decreases until late December and then increases until late June. Temperature on the other hand is highly variable. This year, the lack of deep cold and periodic spring warmth has tricked many of early bulbs to break ground weeks ahead of their normal cycle. Nearly all bulbs need a cold period to produce flowers and the cold period needs to last 12-16 weeks or 3-4 months in order of the bulbs to rest and then regrow. Even with the relatively mild winter, our temperatures have been cool enough to give the bulbs their needed dormancy period.

daffodils break ground.jpg

The leaves of spring bulbs are much tougher than their summertime counterparts. The cellular structure of the leaves is such that they can handle the freeze thaw cycle of late winter and early spring. These types of bulbs include daffodils, tulips, crocus, and the like. The fact that the leaves have already broken ground this time of year won't harm the bulb. What you may notice is some browning of the leaf tips and an earlier bloom. I have also observed that some bulbs don't flower as well after not having a nice blanket of snow. In the future, you could take some evergreen branches, like those from your Christmas tree, and cover the emerging bulbs with the branches. If you don't have a tree, cut some greens from the woods or use some hay. Keep some soil visible by not piling on the greens or other material too thick. Remember, tulips and hyacinths decline anyway after few years, I treat them as annuals.

So what about those shrubs that have their buds opening or already opened? Shrubs that flower early set their buds last summer. In other words, those flower buds always sit dormant through the winter. Plants like lilac, forsythia, rhododendron, magnolia, early dogwoods,and others that flower before mid-June may start to come out of dormancy earlier than usual with the warm weather. The plants themselves will not be harmed. However, some of the flower buds could end up being killed if they open too much and then we get a blast of arctic air. The cold air will be able to penetrate into the buds and thus the plants will not be as floriferous as they potentially could have been. The cold air basically dried out the flower buds.

The one group of planting that may actually be harmed more than usual are plants that are wintered over in containers. This applies particularly to some evergreens or plants that are marginally hardy. The worst thing for plants in containers is to have the soil freeze and thaw through multiple cycles in the winter. The reason for that is the warming takes the plants out of dormancy and then the rapid return to cold can damage various parts of the plants. The damage often shows up in the spring when parts or all of the plant dies. Wrapping a container in burlap can help. The good news is that we have just not seen much in the way of deep cold after our mild days. We hit 45°F, 50°F or even 55°F for a day or two but then our "cold is only 20°F. That isn't that cold. Another I would suggest you use an antidesiccant on any container plants that have shown problems in the past. The product can be applied on a dry sunny day with the temperature above 35°F. You shouldn't have any trouble finding a day or two that fits that criteria over the next week.

Although it looks colder for a few days at the end of this week, I still don't see any prolonged cold or snow. It looks like the plants may have the right idea by getting a jump on spring. My weather crystal ball says some storminess looks to return to our area just after Valentine's Day. Keep checking for updates.


Follow me on Twitter at @growingwisdom and check out my latest videos at GrowingWisdom.com

This blog is not written or edited by Boston.com or the Boston Globe.
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About the author

David Epstein has been a professional meteorologist and horticulturalist for three decades. David spent 16 years at WCVB in Boston and currently freelances for WGME in Portland, ME. In 2006, More »
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