We had daily highs above freezing, some days up into the 60's, some nights above freezing all night. In a search for "plant records" I have a quirky goal of finding plants flowering in every month of the year. So I went out looking for flowers on January 29. Some species do not need many days above freezing to launch their buds.
|Erodium cicutarium, redstem filaree, Jan. 29, 2015|
But it is January, the depths of winter in the northern United States. How can plants be flowering?
Global warming? Maybe. All over the world they are recording earlier and earlier warm temperatures.
However, I want to think about how plants respond to unseasonable weather.
Here in northern Colorado, some years it can be warm the last week of January, other years bitter cold, and likewise on, say, October 8, very hot one year and have a killing frost the next.
We have about the maximum temperature variaton here because Colorado is in the center of North America, therefore in the center of the world's second largest continent. Bodies of water buffer temperature fluctuations, so the centers of big continents have the greatest temperature variations on earth. Colorado usually has 30 degrees F difference between the daily high and daily low, and it can be more. That variation is expressed between days, the high could be 70 one day and 40 the next, no problem. Likewise, the same calendar day in different years can be very warm or very cold.
Plants have to cope with that. There are two basic patterns. One is to avoid responding to unusual temperatures, for example early warm periods. There are numerous ways to do that. One is to track day-length and not grow until the hours of daylight reach a particular level. For example, when day length is 12 hours, it is the equinox, March 21 and past the worst of winter here. Another mechanism is a built-in timer: so many days are needed for enough of a chemical to build up or break down before the plant will grow. If that chemical responds to time not weather, it will keep the plant from sprouting in an early warm spell. Such plants are dormant in January and will be for some time because severe frost has occurred in northern Colorado as late as May 15.
|Mid-fall. There hadn't been a frost but the tree on the left had lost its leaves|
in anticipation of winter while the leaves of the tree on the right
had not even changed color.
|redstem filaree, flowering in January 2015|
Plants with different cues can be found throughout the growing season. In the picture below, the set of gray stems in the lower left are a hibiscus plant that will not sprout until about the first of June, requiring warm air and soil temperatures. In contrast, in the picture the iris and tulips have green leaves and the redbud (tree) and a red tulip are already flowering. They risk a severe snowstorm killing their leaves and flowers, while the hibiscus will not emerge above ground until that danger ihas passed.
|In the lower left, the hibiscus is dormant--beige|
stems and no sprouts, while the iris are up and
the red bud (tree) and tulip are flowering.
I found a second species coming into bloom on January 30: dandelion, Taraxacum officinale (sunflower family, Asteraceae). The leaves had not turned green and yet there was a well-developed flower head. It was half-open at 10 am and probably fully open by early afternoon.
|Dandelion opening its flower, Jan. 30, 2015|
January flowers are rare but substantial warm spells do happen. Plants that will flower in a January warm spell are very much the minority, however. Most plants are still dormant and have not even started to turn green. In an average year, it will turn very cold and snow several times in February and March and the plants that wait do better. But exceptional years happen. Perhaps this is one.
Note added February 8: we have had two snow storms since I found the January flowers. On one day the temperature did not get above freezing and the overnight low was 21 F. Three days ago the field where I saw these plants was under an inch of snow. I think the flowers pictured above were lost and the plants will have to start flowering all over. And yet, we have a week of temperatures in the 50s in the forecast, so no doubt many redstem filarees and dandelions will be sending up flowers again by next week. It isn't easy to be a plant in a mid-continent environment.
Comments and corrections welcome.
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