A root trainer, root-training pot or root pruning container is an aid to the
cultivation of young plants and trees in nurseries. There are many different
designs of pots that will train the roots. One example is a truncated
plastic cone in which a seedling is planted. There is a drainage hole at the
bottom and the main tap root tends to grow towards this.
What this achieves is to encourage the roots the grow a denser system of
root hairs. How it does this is to have the pots designed so as to air prune
the roots. The advantage is when the plant is planted into its home
environment it has a stronger root base to start with.
When polythene bags are used instead, this root tends to go through the bag
into the ground and is then broken off when the tree is moved for planting.
The other roots are insufficiently developed to cope with the shock caused
by this and so the tree's chances of survival are reduced. The root trainer
is mounted in a stand above ground so that, when the tap root emerges, it is
dried by the air. This air pruning causes the root inside the pot to thicken
with stored carbohydrates which will support vigorous root growth when the
plant is put into the ground. The other lateral roots of the plant grow to
compensate for this and so a stronger root ball is formed which improves the
When raising multiple seedlings, the root trainers are commonly placed in
trays or racks. The size of each trainer depends upon the species but, for
broad-leaved trees, the capacity will be about acup. Vertical ribs inside
the trainer are positioned to train the roots to grow downwards and so
prevent root spiraling.