Field Growing Trees for Bonsai

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General care and maintenance of Field-Growing Trees

One of the benefits of field growing is that a large number of trees can be planted out for future use as bonsai and left to their own devices without the need for high maintenance care.

Before planting, improve the condition of the soil though it is not necessary (or possible) to expect a soil of the standard used for container growing. Clay soils should be improved by adding grit, sand or compost to open up the soil and improve drainage, thin gritty soils should have compost added to improve water retention and nutrition.

For their first season after planting out or after rootpruning, care must be taken that the ground is not allowed to dry out more than a couple of inches below the soil surface as the rootsystem will not have had a chance to extend in search of moisture. However, do not keep the soil continually wet as this will actively discourage the roots to grow in search of moisture, making the tree less drought resistant.

Trees over 3 or 4 ft that have shallow a rootsystem should be staked to guard against being upturned by the wind. Tie the tree to a stake using tree-ties to reduce damage to the bark on the trunk. Try to tie the tree low down on the trunk; though it is necessary to steady the base of the tree to stop the roots being disturbed by the wind, repeated flexing of the upper part of the tree in the wind will help thicken the trunk.

Keep weeds that grow around the trees to a minimum especially around young trees that may not be established enough to compete for light or water. Be wary of weeds that might shade out and cause the eventual dieback of lower branches.

Weed suppressing membranes can be used on the soil surface prior to planting; this will keep weed growth to a minimum but can cause difficulties in future years when trying to rootprune or collect your trees. It should also be noted that the presence of low-growing weeds will be of no detriment to the tree and can greatly reduce the time it takes for mature bark to appear.

Regular feeding of field growing trees is unnecessary though they do benefit from one application of Growmore (or similar slow-release fertiliser) in the Spring and one in the Summer, particularly on thin, stony soils.

Pruning Field Grown Trees

Primarily, the purpose of field growing is to develop a thick trunk base and nebari. Until the trunk has developed, there is no need to consider the final branch positions (unless the tree is coniferous). Ordinarily, once the trunk has reached its final size and girth, all branching will be too thick for use as bonsai and will need to be removed and restarted.

Avoid continually interfering with your tree! Any pruning will result in less growth and less increase in trunk diameter. Bear in mind that the more growth the tree carries, the thicker the trunk will become and the more growth it will put out during the forthcoming season.

The only pruning that should be necessary is during the Winter in order to control or redirect the trunkline depending on how you envisage the finished trunk to look. (An article on developing field-grown tree trunklines can be found here).

Rootpruning Field Grown Trees

Rootpruning your field grown trees will slow down their growth rate and negate the purpose of field growing. However, it is important that the future nebari and root structure is developed or there is a risk that your fat field-grown trunk will be ruined by a poor nebari.

Rootpruning should be carried out in early Spring as with bonsai. Roots should only be pruned to encourage a good nebari. Every second or (preferably) third year, lift the tree and examine the root structure. Any roots close to the trunk that are felt to be unsuitable for future use (for instance crossing roots, roots growing at poor angles from the trunk, a thick over-dominant root or very straight roots with little branching or taper) can be removed. Unless you have had the foresight to plant the tree on top of a tile, it is also important to remove or at least shorten any downward growing roots. Try to remove as little root as possible and no more than a couple of major roots in one year.

In the last year or two before finally lifting the tree to begin bonsai training, cut around the base of the tree with a spade in early Spring to encourage finer root growth closer to the trunk.

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