Article and pictures by David Marks.

BEST CONTAINER FOR A JAPANESE MAPLE

Stone or terracotta are best for a couple of reasons. First and most importantly, their weight (compared to lighter containers) will help prevent them from being blown over in strong winds. Choose containers with a base that is wide enough to stand well.

Wood containers look very attractive and they also have substantial weight. However they may well require treatment to prevent the wood from decaying and the treatment may damage your Japanese Maple.  Make sure any container you use has good drainage holes in the base.

Plastic and metal pots are best avoided because they blow over to easily. They also have the problem that they do not allow the easy transfer of air between the soil and the outside.

Most Japanese Maple trees are sold in pots which can be used for five years or so before the tree needs to be re-potted. Avoid bulbous, rounded pots because when the time does come for re-potting the only way to remove your Japanese Maple will be by breaking the container. All containers should have adequate drainage holes in the base.

The size of pot should be appropriate for the size of the tree. Simply looking at the pot size in relationship to the tree size is normally enough to allow selection of the correct size of container. However, as an example a 30cm (1ft) square pot supports our 140cm high Japanese Maple very well.

WHEN AND HOW TO RE-POT A JAPANESE MAPLE TREE

When you buy your Japanese Maple tree it may require immediate re-planting or after several years it may outgrow the existing container. The best time of year to re-plant a Japanese Maple tree is in late winter to early spring. First select a new container as described above.

The next decision is which soil to use. Japanese Maples prefer a slightly acidic soil so potting compost for Rhododendrons, Azaleas or ericaceous plants is suitable. Another solution is to use a loam based compost which is slightly acidic. John Innes sell their own ericaceous mix which is an ideal choice especially if about 20% of sharp (not builders) sand is mixed in.

If the container has
previously been used then scrub it clean of all the old soil residue. Add about 4cm (1½in) of smallish stones / broken pot pieces into the base of the container – this will help to ensure good drainage.

Remove the tree from its old container and lightly brush away some of the compost from the root ball and the surface. If the root system is compacted, gently tease out some of the roots from the old compost. Add some compost into the new container and then transfer the Japanese Maple onto the compost.

It will be necessary to add or remove some compost to ensure that when more compost is added it comes to the same level around the main stem as it was in the old container. Add new compost, a few centimetres depth at a time, and lightly firm it down. Don’t compact the new compost but do ensure there are no air-pockets in the compost.

Fill up with compost to about 5cm / 2in from the top of the container. Add about 2cm / ¾in of chippings to the surface of the compost. It is well worth buying a bag of chippings which finishes off the surface nicely as well as deterring weeds and pests.

Water well with rain water (rather than tap water) if possible. It is also a good idea to buy container supports which will keep it off the ground. This ensures the best possible drainage and stops the base of the container becoming a home for all manner of insects and bugs.

CARE OF JAPANESE MAPLES IN CONTAINERS

Japanese Maples growing in containers need only minimal care but they do appreciate it frequently. The first rule is to try and maintain a constant supply of water in the compost without over-watering. Even two or three days of warm, sunny weather without watering can do them a lot of harm.

If you plan a holiday in the summer the ideal is to ask your neighbour or friends to water your Japanese maple(s). If that is not possible then move them into a shaded and cool position. If your area suffers cold winters and or high winds then place your Japanese Maples in a cool greenhouse or garage from late December onwards and bring them back into the garden in early Spring.

Feed twice a year with a slow release fertiliser such asblood, fish and bone. Apply a good handful and work it gently into the top of the soil. The first feed should be in March and the second feed in June. Do not feed your tree with nitrogen rich fertilisers, they will promote week foliage growth which can be damaged in winter time.

An annual prune in early June should remove any damaged or wispy stems particularly in the centre of the tree. Pruning can also be done to maintain the shape and size of a Japanese maple tree.

WINTER CARE OF JAPANESE MAPLES

There are two principal considerations when looking after Japanese Maples in containers during the UK winter. The first is to prevent the soil from becoming water-logged by winter rain. As mentioned above, Japanese Maples are tolerant of many conditions but they do not appreciate large changes in the amount of water in a container.

The second factor to watch out for, as with all containerised plants, is to avoid the soil freezing over for long periods of time. Japanese Maples have a fibrous root system which is easily damaged by protracted periods of frost. It is possible to insulate the containers but this only delays the frost.

With the above two principals in mind our advice is to move your Japanese Maple into a warmer and more protected position during periods of frost in the winter. The ideal position would be in a cold greenhouse. This will protect your tree from the cooling winds and give some protection from frost. If you do this though, be sure to remove the tree from the greenhouse at the first sign of warm weather – greenhouses can become surprisingly hot very quickly in only moderately warm weather.

Most of us don’t have greenhouses however so a good alternative is at the back of an open garage. Don’t be concerned about the lack of light because in winter Japanese Maple are basically in hibernation. As with greenhouses, move the tree back into the open after the frosts have passed.

If you have neither a a greenhouse nor an open garage then do not be tempted to move the tree inside the house. Conditions there will too warm and the air too dry. The best option is to search out the most protected position near the walls of the house. House walls will be relatively warm in winter and can protect your Japanese Maple tree from the worst of the frost. Also look for a position which protects from wind and reduces the amount of rain that falls on the soil in the container.

One particular position to avoid in winter for Japanese Maples is an East facing one. That particular position is liable to receive morning sunshine and warmth after a freezing night. This repeated sudden change in temperatures is not good for the containerised trees. Far better a West or North facing position which will warm up slower in the mornings.

BEST JAPANESE MAPLE VARIETIES FOR CONTAINERS

Japanese Maples are expensive plants to grow and if you buy a fully container grown variety which is sold as suitable for containers it is more then likely to be, at the very least, an acceptable variety. Our particular recommendations (click the name for a fuller description) of easy to acquire varieties are:

• ‘Corallinum‘ – beautiful shape, coral pink leaves
  initially turning green then scarlet
• ‘Crimson Queen‘ – red throughout the year, a
  classic for containers
• ‘Deshojo‘ – deep red leaves, often also used for
  Bonsai cultivation.
• ‘Ornatum‘ – very red leaves in autumn, for
  those who admire thin feathery leaf types.
• ‘Garnet‘ – similar to Ornatum above but the leaves
  are slightly coarser. An excellent choice.
• ‘Lemon Lime Lace‘ – the name says it all,
  thinly dissected light green leaves
• ‘Oshu Beni‘ – a tough tree, leaves are initially
  red then turn green and then red again in autumn