Trees in containers can be used to frame doorways, provide a focal point and are ideally suited to small gardens, courtyard gardens or patios. Problems associated with tree roots or suckering from plants such as sumach can be avoided by growing trees in containers.
Ideal
subjects for containers include trees suitable for topiary,
such as yew, holly and box, and fruit trees on semi-dwarfing
rootstocks such as M9. They are useful for cultivating tender
plants such as citrus or olives, which can be moved to frost-free
conditions in winter.
In most cases growing a tree in a container will restrict its ultimate size. It is still better to avoid larger, fast growing trees except for shorter term planting, as they may become too large and prone to toppling over. Trees tolerant of coppicing are another possibility including Liriodendron tulipifera, Eucalyptus and Salix.
Containers
Terracotta pots provide weight for stability but should be frost resistant. Lighter plastic pots are better if plants require moving around. Pot plants up in stages, aiming for minimum final pot size of 45cm (18in) if the plant is to be moved around. Larger pots can be used where trees are to remain in situ all year round.
Compost
A loam-based compost such as John Innes No 3 is best in most cases and provides weight for better stability. For plants requiring ericaceous soils use ericaceous John Innes composts or an ericaceous multi-purpose compost. Place 5cm (2in) of crocks or gravel over drainage holes and raise pots on feet in winter to avoid waterlogging.
Care
Container-grown trees are more prone to drying out and need regular and thorough watering. Several waterings may be needed to wet the full depth of compost. Use rainwater for ericaceous plants, although tap water is better than none if you run out.
Apply a controlled-release fertiliser at the start of the growing season or use a liquid feed at regular intervals.
Refresh the compost in spring by removing 5cm (2in) of dry, loose compost near the surface and replacing it with some fresh compost mixed with some controlled-release fertiliser. If trees are tolerant of root disturbance, every three to five years remove the tree from its pot and tease out the roots loosening the old compost. After trimming the larger roots, repot in fresh compost.