Containing Success

Traditions are hard to break. From the first time I planted a containerised tree I had grave doubts over the sustainability of the root system. So often amass of fibrous and spiralled roots is applauded, but I have always thought of the mass as a time bomb waiting to explode.

My first experience of this was after viewing an avenue of Pinus nigra Austriaca on a roadside verge in Surrey. The trees had been planted as 4 litre, 60-90cm tall plants and by the time I saw them they had grown to over 3m in height, each supported by heavy grade stakes.

Within a week of the stakes being removed the trees had fallen over and on closer inspection the old 4 litre pot volume had developed into a block of wood with three or four prongs of root protruding.

Problem roots

The cause of this lack of anchorage started the moment the young pines were establishing in black pots. As their roots developed and reached the sides of the container they began to spiral randomly, forming a knotted and tangled root system. At secondary thickening the roots knitted ever closer and were never allowed to establish to form the anchorage that was necessary to sustain the weight of the plant above ground. Fatal results were inevitable. 

Shrubs rarely attain sufficient weight above ground for this lack of anchorage to matter, but even here when a plant is pot bound (grown in the same container for over 12 months), the root system may not be adequate to support vigorous growth. However, any plant grown in a black pot that has the capacity for growing into a tree has a good chance of its life span being seriously impeded by poor root development.

As a nurseryman, growing trees in black pots that may well fail at a later date seemed pointless. My aim was to find a way of producing container tree stock that would thrive through to maturity after planting. Traditionally, trees have been lifted from the ground in the autumn and winter and delivered bare-rooted to a site where they were heeled-in and planted when possible.

Typically a consignment of 200 trees delivered for planting at a new development would arrive on site having been lifted from a nursery field about a week earlier. The contractor may plant up to 25 large trees per day, so by the time the first 100 have been planted the balance could have been out of the ground for two weeks. The consequence of this is seen the following summer when the site is littered with either dead or dying trees.

Trees should be treated like fish out of water when they are handled bare-rooted, as they still have a demand for water with no means of getting it. Good husbandry lengthens the time a tree is able to survive out of the ground before planting, but for many varieties the period the tree is out of the ground is too long to ensure survival.