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PERMAFROST AND HORTICULTURE

Gardening on permafrost has problems all its own. In permafrost soils, only the top few inches thaw each year. Moisture cannot penetrate the frozen layer beneath. Any moisture is then trapped in this thin layer causing cold, wet soil conditions. The soils tend to be acidic as well. When the existing vegetation is removed from the site, the soil will thaw to a deeper depth and the soils will drain better. When used for a garden, the soil should remain workable, but if permanent landscaping material is planted, the original cold, wet condition will return in time, due to shading by the plant material. Trees and shrubs tend to have shallow root systems because the soil 12 to 18" down will be at or near the freezing point. This restricts the plant's ability to absorb moisture and nutrients. In the southern areas, trees suffer from lack of water and aeration when fill is placed over their root zones. With permafrost soils, the addition of fill causes the cold zone to move upwards proportionately to the depth of fill. This brings the freezing temperatures up into the existing root zone. The roots will no longer be able to supply the tree with nutrients and water and death will occur.

To increase soil temperature for the garden, the soil can be built up into ridges, terraces or raised beds. This will raise the temperature as much as 4°F (2.2°C). Polyethylene mulch can also be used to warm the soil. Together ridging and poly will increase the soil temperature by 16°F (9°C). This method is excellent for root crops such as carrots and potatoes. To grow crops like tomatoes and peppers in the far north, the use of crop shelters is recommended. These are portable greenhouses that can be assembled each year on site. They are often built in modules that are fastened together as required. Generally they are constructed of wood and polyethylene. They are unheated but serve to trap the heat of the sun raising the air and soil temperature sufficient to mature the crop.

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permafrost.html
This page by Pat
updated August 18, 2000

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