This weekly column is being reproduced with the permission of Steve Smith, The Whistling Gardener, and owner of Sunnyside Nursery in Marysville.
I just returned from spending two deliciously warm and sunny weeks in Mexico doing as little as possible while the rest of you endured “Snowmageddon” and some nasty freezes that pretty much put the skids on any productive work in the garden.
With that kind of weather I would have expected my garden to look about the same as when I left it fourteen days prior but I discovered some surprising changes.
While I was gone my little Winter Aconites woke up and came into bloom with their bright and sunny yellow flowers that aren’t much more than two inches tall but sure can illuminate a shady bed.
The Snow Drops were starting to emerge before I left and are now six inches tall and in full bloom in sweet little clumps scattered throughout the garden under trees and shrubs where it will stay cool and shady during the summer when they are asleep.
I have patches of daffodils that were nonexistent two weeks ago that are now eight inches tall and could easily be in bloom in another ten to fourteen days.
I also saw a few clusters of tulips that have been in the same place for several years that are already four to six inches tall. And of course my wife’s Scillas are all over the stinking place despite my aggressive culling after they bloom every spring.
Bulbs as a whole seem to be indifferent to winter temperatures and will proceed with their growth regardless of whether it is a normal winter or one that is excessively cold.
The same is mostly true for perennials. Case in point is Oriental Hellebores. Over the last two weeks mine have gone from just barely showing any sign of potential blooms to vigorous clusters of ten to twelve inch flower stems, which will continue to elongate over the next couple of weeks until they are in their full glory at around sixteen to eighteen inches tall. When one is gone for two weeks these transformations become quite evident.
While bloom times for spring bulbs can vary by a couple of weeks, they are mostly predictable and my theory for that is simply that bulbs (and perennials) are more responsive to soil temperature rather than air temperatures.
Air temperatures can fluctuate wildly but soil temps (especially in the northwest where the ground rarely freezes) remain fairly constant. In the winter they seem to run about ten degrees warmer than the air and in the summer ten degrees cooler. The deeper you go the less variation there is. At around five feet deep the soil temperature is basically constant.
For an interesting article on soil temperatures check out Cliff Mass Weather Blog, Soil Temperatures and Gardening, Sunday May 6, 2012.
To further reinforce my hypothesis I offer two more examples from my garden.
First, I have a Sarcococca ruscifolia shrub that is growing in my front drive surrounded by asphalt and underneath a deciduous birch tree. It is only two to three feet tall and is in full fragrant bloom. The protection of the birch tree and the additional heat from the asphalt have countered the cooler air temps and so it is blooming when it normally does. On the other hand, my Cornelian Cherry has yet to bloom (three to four weeks behind schedule and
counting) due to the fact that the blooms are ten to twelve feet above the ground where the cool air is able to slow everything down, irrespective of what is going on down in the ground.
Steve Smith is owner of Sunnyside Nursery in Marysville and you can send your gardening questions to him at firstname.lastname@example.org.
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