The Homeowners Column

The Homeowners Column

So What Does a Warm Winter Mean for our Plants?

Photo of Sandra Mason

Sandra Mason
State Master Gardener Coordinator
slmason@illinois.edu

Snow on the snowdrops. Honestly I would rather see sun on the sunflowers, but here in Illinois we can count on heat in the summer and cold in the winter. Well, sort of. For January 2012 the statewide average temperature for Illinois was 31.4 degrees F, which is 6.6 degrees above normal and the 13th warmest January on record. I can't remember a January as mild.

Illinois is enjoying its 6th warmest winter since 1895, according to State Climatologist Jim Angel of the Illinois State Water Survey (http://www.isws.illinois.edu). I guess I hibernated through the second warmest winter, 2001- 2002, with temperatures 6.1 degrees above average. I was not even a glimmer in my parents' eye during the warmest winter winner which was 1931-1932 with temperatures 8.2 degrees above normal.

For us warmer winters mean lower heating bills, easier driving and maybe even a round of golf in February. So what does all this mean for our landscapes and gardens? Generally temperate zone plants (winter hardy trees, shrubs and flowers) need a cold period to initiate growth in spring, to promote flowering and even for some seeds to germinate. In other words they have to go through a minimum of hours of cold to be healthy, happy plants which in turn promotes healthy, happy gardeners.

The fancy word for this necessary cold period is vernalization. The time period and the cold temperature requirement vary between species. The length of daylight and maturity of the plant also effects growth and flowering, but that is another chapter to the story.

Spring flowering bulbs such as daffodils and tulips need a set cold period to flower properly, usually about 13 weeks between 35-45 degrees F. The actual flower buds are formed during the previous dormant period, but the low temperatures are necessary to overcome dormancy and initiate the lengthening of the flower stem. Florida has winter warmth, but Florida gardeners have to purchase pre-cooled tulip and daffodil bulbs.

The good news, in relation to warmer than normal winters, is that freezing temperatures are not essential to satisfy the requirement for most temperate zone plants. For example most perennial flowers will grow and flower well after 6-8 weeks of cooling at 41 degrees F. So even though soil temperatures have been higher than usual, perennial flowers and bulbs should flower just fine.

For fruit trees the temperatures for the cold requirement are between 35-55 degrees F with 45 the most effective temperature. For example the required cold period for apple varieties vary between 800 to 1,100 hours of 45 degrees or below. However winter temperatures can get too high and actually devernalize a plant. Although we love 70 degrees F in winter, four or more hours of daily temperatures of 70 and higher can actually negate the cold period that was received by the plant during the previous 24 to 36 hours.

So the good news is plants have experienced enough cold to break dormancy and grow on to be happy plants. If February temperatures remain moderate between the average high of 37.7 (for Champaign-Urbana) and the average low of 20.2, our plants and our pocketbooks should enjoy the remainder of the winter. However temperatures severely below normal (10 degrees or more) may translate into damage of flower buds on ornamental and fruit trees depending on their stage of flower development.

I know a "wish for snow" will jeopardize my standing with some folk, but if severely low temperatures are a possibility a good snow cover can insulate perennials. Otherwise throw a nice blanket of shredded leaves over any newly emerging leaves.

March 10th Join Vermilion County Master Gardeners and me for Garden Day in Danville. Garden programs and shopping. PH: 217.442.8615 http://web.extension.illinois.edu/cfiv/

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