It’s a common practice on the Prairies to cultivate in the field, garden and around trees.
Often rototillers are used to churn up the soil in spring and fall to work the ground deep, especially in gardens.
This deep cultivation around trees, however, is hard on their root system.
For a tree, it’s like having part of its digestive system cut away, said Shelley Barkley, of Alberta Agriculture’s Crop Diversification Centre South in Brooks.
“Large trees can have thousands of feet of root system,” she said.
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“Much of this root system is out beyond what is commonly referred to as the drip line. The drip line is the circle around a tree at the tips of the branches and is the place where it’s often recommended to add fertilizers or soil-drench insecticides.
“However, tree roots can be found from the tree at a distance of at least twice the height of the tree crown.”
Most trees don’t have a taproot. Instead, their roots spread.
Some roots are deep, supplying moisture and stability.
But more than 95 percent of a tree’s roots are within the top one metre of soil and can be as shallow as seven to 10 centimetres.
“Tree roots grow where the soil temperature, moisture, aeration, pH nutrient supply and soil structure is correct,” she said.
“The greatest number of roots will be at soil surface – just under the leaf litter in a forest or intertwining with grass roots in the lawn.”
When deep cultivation cuts through roots, trees will respond in many ways.
“A sample of caragana that had leafed out and then began to wilt and die was sent into the lab at Brooks,” Barkley said.
“The diagnostician concluded that cultivation 15 cm in depth had been done at a vulnerable time in the plant’s leafing out process.”
Some trees, such as poplars, will respond by sending out suckers, but they too can get stressed as their root system is pruned time and again.
Spruce and pine may lose more needles than normal in the fall or spring.
Although deep cultivation isn’t often diagnosed as the direct cause of decline in trees, it adds to stress levels.
To manage the cultivation cycle and improve the health of trees:
- Cultivate no deeper than about 2.5 cm, just breaking the soil surface
- Put down mulch around trees. This keeps the roots cooler, maintains soil moisture levels and helps keep weeds down.
Mulch may have to be pulled back from the trunks of trees for winter to prevent mouse damage.
