Home & Garden: Snowdrops flower early in western Colorado
Free Press Gardening Columnist
Galanthus are showing up in my yard even though they usually don’t appear until sometime in March. Known by the common name of snowdrop, these flowers can bloom in winter when the weather is warm. Each plant produces one small (one inch or less) white flower, which hangs down from its stalk like a drop of water just before it opens. Once opened, its three white petal-like sepals arch out over three inner petals giving the appearance the blossom has six petals. As with other bulbs, snowdrop has narrow leaves approximate four inches long.
Members of the Lily family (Liliaceae) are known to have flowers with parts in threes, and the sepals and petals are usually identical in size and color. There is a difference between sepals and petals as any botanist would tell you. Most sepals are green and subtend the petals; in other words they are located beneath petals.
North America has 75 genera of lilies. While not all of these are hardy enough for western Colorado, gardeners can have a very wide selection of the different Liliaceae genera. Worldwide there are 250 genera and 3,700 species.
My snowdrops are naturalized in my front lawn. They were planted years ago and have multiplied and spread throughout the buffalograss lawn over time. Sometimes plants bloom at the wrong time of year, expending a great deal of energy in the process. If their leaves die too soon, they can’t replace this energy through photosynthesis and will have a tough time recovering from the rigors of blooming.
It is possible crocus will start popping up next as they usually follow the snowdrops. Later on the tulips and daffodils will appear. Hopefully my other flowering bulbs will wait a few more months before poking their heads above ground. The appearance of the snowdrops reminded me I have some bulbs and corms in the trunk of my car, which I plan to get into the ground within the next few days. The soil has been warm enough that many areas have not yet frozen, so using a bulb planter to cut a hole in which I will drop a bulb or corm should be quite easy.
Chilling degree hours, also known as chilling accumulation, awakens plants from dormancy (their sleeping stage). Once buds enter dormancy in the fall they are able to tolerate temperatures much below freezing and will not grow in response to midwinter warm spells. Plants in this sleeping stage remain dormant until they have accumulated a certain number of chilling units (chilling hours). Once our temperate-zone plants have received enough chilling hours, the buds are ready to grow in response warm temperatures.
As hardy bulbs, snowdrops also require a period of winter chill to initiate growth and bloom. Fifteen weeks of temperatures between 45 to 50 degrees appears to be sufficient for snowdrops. In the case of trees and shrubs if the buds do not receive adequate chilling temperatures during the winter, they are not completely released from dormancy. In the case of fruit trees, temperatures below freezing or above 60 degrees is not effective for chilling units accumulation. While different trees have different temperature requirements, based in part by the latitude in which they evolve, many woody plants require the temperature to be between 32 and 45 degrees per night for chilling accumulation to occur.
The lack of adequate chilling units accounts for some of the delayed defoliation, and reduced fruit quality of some trees and shrubs. Warm winter weather may not provide adequate chilling units and we may see symptoms of this come spring. What we need is a cold winter, but not too cold for adequate chilling accumulation to occur. An abundance of snow especially in the mountains is also desirable to ensure we have adequate moisture in the Colorado River to share with the other seven states that use Colorado’s water.
Free Press columnist Dr. Curtis E. Swift is a retired horticulture agent with the Colorado State University Extension. Reach him at Curtis.Swift@alumni.colostate.edu, 970-778-7866 or check out his blog at http://SwiftsGardeningBlog.blogspot.com. He owns Swift Horticultural Consulting and High Altitude Lavender.
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