The Root Spiral
Growing conditions of plants are fundamental for the quality of their roots.
Growing in open ground
This growing method, less and less used for retail sales, is still very much used by professionals, especially for medium- and large-sized plants. Its the best way to produce sturdy, dense and well-shaped trees.
For the individual, it isn't really an "instinctive" buy because you have to go through the aisles of the garden centre, then prepare the plant (5 to 15 mins.), or order it.
Growing in containers
This is a very popular method, as it gets rid of the inconveniences of open ground, as well as extending the planting season, as all the roots are contained in the pot, which you simply remove the plant from before putting it in the ground.....but:
Inconvenience No.1: the plants are not very dense, especially if they are a few years old (and on condition that they are repotted every years in a bigger pot!).
Inconvenience No.2: some plants with strong roots form what we call a "root spiral": their long roots turn in circles at the bottom of the pot and must be cut before planting in order to prevent auto-strangulation. These plants shouldn't be grown in containers...nonetheless, a lot of people do this!
Warning: even plants grown in open ground may have spiralled roots!
Most young plants with a delicate growth are multiplied in pots before being planted in the ground, which means that the roots have already spiralled in a very small diametre. This is a heresy! Unfortunately, this is widely practiced in ornamental nurseries.
To overcome this inconvenience, there are procedures to avoid roots from spiralling:
- The biodegradable peat pot for young plants
- The forestry pot for trees with pivotal roots
- The above-ground basket for trees and conifers 2 or 3 years old.
The forestry pot (20cms. deeep) allows the pivotal root not to bend when it touches the bottom of the container.
The peat pot and the above-ground basket (1 to 4 litres) both allow an "aerial encircling" of the roots. That is to say that the roots dry out when they grow outside the walls of the container, which encourages the growth of other roots on the inside, which in turn grow out, and so forth...
Which plants are most likely to be affected by this phenomenon?
Those whose roots don't branch out much, especially those with pivotal roots. Indeed when there are few roots, they tend to lengthen, whereas dense, thin roots branch out much more, at the same time thickening less. Spiralled roots must be avoided, especially for future big trees.
Bushes are not generally effected.
The most affected are trees like oaks, walnut trees, hickory trees. And conifers such as pine trees, fir trees, spruce trees and redwoods.