Home & Gardening: Protecting plants from snow
Free Press Gardening Columnist
The weather has been quite nice this past week, with the highs being reported in mid to low 30s. While these temperatures certainly won’t eliminate the snow in the more shaded areas of the Grand Valley, the snow in open areas should be pretty much gone by the time you read this article. (I wrote this on Monday, so don’t get too upset if we had a major snow storm since then).
I would prefer an open winter in the Grand Valley with little if any snow. Snow causes problems with a lot of woody plants due to the reflected heat off the snow. While the resulting sunscald and damaged branches of shrubs can be removed, sunscald damage to tree trunks is guaranteed to have a lifelong negative affect on the health and development of damaged trees. The rough bark seen on the south-west side of young trees is a sure sign of the winter sun damage. We will likely have more snow, so get out there and wrap those trunks with an approved tree-wrap. At least that will prevent additional damage.
Some alpine plants die when snow covers them up. Winter wheat on the other hand is protected from winter damage when as little as two inches of snow covers the plants. The key is whether the winter wheat is well hardened or conditioned when entering the winter season. As with many other plants, winter wheat properly hardened may withstand temperatures at the crown of the plants of about four below zero; less hardened cultivars, about 3 degrees Fahrenheit.
Last week when my last set of young lavender plants were covered with a frost blanket, there was about 4 inches of snow covering the planting beds. Even though this layer of snow had been there for some time, only the top inch of soil was frozen. The soil beneath the frozen layer was soft and friable. While this made it easier for us to push in the sod staples used to hold the fabric in place, I would have preferred the frost line much lower. Continued root growth in warm soil when air temperatures are freezing can use a great deal of the stored energy the plant needs to recover in the spring. While most root growth ceases about 40 degrees Fahrenheit, colder would have been better. That does not however mean the plants stop all activities during the winter. It still needs an adequate supply of moisture in the soil.
Snow is an insulator keeping the ground surface essentially at the freezing point throughout the snow season. This is in part due to the capacity of the soil to retain heat while snow and other insulating materials trap heat in the ground. The latent heat of the soil is also involved, with the frost line even rising in mid-winter due to the release of this heat energy.
Snow helps retain soil moisture except when snow cover is sparse and the air is dry. When the latter occurs the soil can lose moisture to the air. Because of the soil dehydrating effects of our winters, winter watering is recommended. While snow can be a benefit, it also can cause problems for plants, even those in perfectly manicured landscapes.
In areas where acid-snow is an issue (even in Colorado), damage to stems, plant crowns, and evergreen leaves occurs due to the extended period the acid snow rests against these tissues. Rain and snow absorb carbon dioxide from the atmosphere resulting in the buildup of carbonic acid. This process can result in rain or snow with a pH reading as low as 5.6. Nitrous oxides, picked up from the atmosphere, and converted to nitric acid also have been reported as major components of acidic rain and snow. Sulfates from industrial sites and coal-fired power plants are converted to sulfuric acid. As liquid water flows downward through the snowpack during the early stages of snowmelt, it become more acidic and flows into streams and lakes killing salamanders, fish and other aquatic creatures. The snowmelt water can also contain mercury and other pollutants.
While snow can be a benefit for our mountains and urban landscapes, it can also be responsible for damage to the ecosystem when it picks up pollutants from human activities. We all know active volcanoes pump a lot of pollutants to include sulfates into the air, but we can’t control those eruptions. We can however be active in attempting to reduce air pollution by being more involved in our own communities’ efforts to reduce the air pollution contributing to acid rains in our mountains and asthma attacks of our citizens.
If you want to get more involved in the clean-air process, I suggest you give Ed Brotsky at the Mesa County Health Department a call. He can put you in contact with Karen Sjoberg with the Citizens for Clean Air, a local grass-roots organization.
GJ 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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