Acer trees (also known as Japanese maples) are elegant, compact, slow-growing, hardy deciduous trees that are ideal for growing in containers and the perfect choice for small spaces.
Choosing your Japanese maple tree
There are many varieties of acer trees, some specifically ideal for growing in containers. The Acer Japonicum varieties tend to make small spreading trees. If you’re looking for more of a shrub-like tree, the Acer palmatum types would be a good choice as they are more elegant and broader than they are tall.
Acer leaves produce striking coloured leaves, changing colour through the growing season, with the same leaves can be different colours at different times of year You will then need to decide on your choice of colour. Newly emerged leaves range from yellow and lime green through to pink, autumn colour range from bright yellow through orange to intense red.
The Right Soil / Compost for Japanese Maple Trees
Although acers in pots are fine in most soil / compost, they thrive best in slightly acidic, humus-rich, well-drained soil. You can achieve this through using an ericaceous (acidic) compost.
ix this in with your own well-rotted organic matter, such as garden compost, for a light but not-too-open soil.
The soil should be well-draining but not to the point where all the water runs straight through.
Adding mulch to the top of the soil will help keep the moisture in. When using organic mulch, you must ensure that it doesn’t make contact with the tree trunk as that damp and dark environment could result in a disease in the tree.
For this reason, non-organic mulch, such as gravel, is recommended. The mulch helps keep the soil temperature warmer in winter and cooler in summer, reducing water loss.
Watering and feeding
Japanese maples in containers will dry out quickly so it is important to water regularly. This could be as much as once a day during hot spells. Newly potted trees, particularly in dry spells, will need a lot of water to aid their establishment.
If your acer leaves are becoming brown and crinkled, this could be due to over- or under-watering. Assess your watering routing to figure out which is the problem and adjust accordingly.
Japanese maples don’t need much feeding. One application of fertiliser for acid-loving plants in the spring should be enough for the entire growing season. Although we recommend organic feeds where possible, Acers benefit from the application of a slow or controlled release type fertilizer.
Commercially known as Osmocote, this is commonly available works very well on Japanese maples. Vitax also produce a specialist Acer feed.
Japanese maples grown in the ground are fully hardy if planted out of cold winds, however those planted in containers, don’t respond well to frost.
Pop your container on pot feet or bricks so the cold does not get into the bottom of the pot and wrap the pot in several layers of bubble wrap or horticultural fleece if the temperatures are predicted to be freezing temperatures for several days. As for Japanese maples planted in the ground, site them in pots away from being exposed to cold winds.
Where possible it is advisable to move the container somewhere warmer and sheltered such as a corner between outside walls.
The Right Size Pot
Ideally, the pot should be two to three times the width of the extended roots. If your tree is still in its original pot then as a general rule your new container should be three times as wide as the tree’s original container.
This general rule assumes that the root ball is the size of that container and the new pot size will give your tree plenty of room to grow its roots out without being too big.
To aid drainage, place some clay pebbles pot shards or large drainage pebbles in the bottom of the pot.
Don’t be tempted to pot your tree from its container into something that is too big thinking that it will save you time in the long run by not having to re-pot, when it could actually kill your tree, unless you ensure that the surrounding compost does not become too soggy. See later advice*
Every 5 years or so your acer tree will need to be re-potted to allow their roots to further grow.
The best time to re-pot your Japanese maple is in late February – early March, just before the buds begin come out. This is because the days will be longer with higher temperatures meaning that your tree will be starting to wake up from its winter hibernation.
Repotting later than this can be more stressful for your tree as it’s channelling all its energy into producing new foliage and the shock of being transplanted at the same time can result in the leaves being spoilt.
You can re-pot these magnificent trees through the summer months as Japanese maples will have done a lot of their growing by then and will happily root into fresher compost. However, it is generally advised to avoid re-potting in the height of summer when temperatures are very high, you may find that the leaves shows signs of stress as it fights to channel enough moisture from the roots to its leaves.
Additionally, avoid repotting your Japanese maple in autumn as the days will be shorter with lower temperatures and your tree will be getting ready for its winter slumber.
Long-term container-grown trees will need root pruning every two or three years. To do this, place the pot on its side and remove the tree. Using an old sterilised saw cut 5cm (2in) off the bottom of the root ball and three or four slivers down the side. Tease out the roots on the surface of the compost and repot with fresh potting compost (same types as above).
Place sufficient potting compost in the base of the pot so the tree is planted no deeper than previously.
Some additional tips for repotting:
Make sure the soil isn’t too wet when repotting, let it dry out slightly first
As mentioned earlier, Japanese maples like slightly acidic Ericaceous composts. We recommend to plant in a John Innes No. 2 potting compost or a peat-free ericaceous with 25% added sharp sand, which gives good drainage.
Keep the compost moist, but not soaking wet, and feed in spring and early summer with a slow-release fertiliser or liquid feed.
Loosen the soil at the edges of the pot and pull the tree out by the base of the main stem.
To allow the roots to bed in, keep the plant watered for several weeks.
To ensure that the water gets into the root ball water at the base of the trunk, and thus avoid it overflowing down the sides of the pot, gently make six 1 cm diam x 2cm deep holes in a circle with a dibber in the rootball about 15-20cm away from the trunk, so that the water passes into the plant rootball.
It is a good idea to dress the surface with decorative grit. The lighter coloured the better.
Best Containers for Acer trees
Japanese maples are ideal for growing in containers. Whichever type of pot you choose, it is essential to choose one that is not too deep as they like their roots to be close to the surface. However, a wide pot is preferable as acer trees like a lot of space around them.
Wooden Tree Planters
Wooden planters are ideal for acer trees as they have excellent drainage and they can hangle their heavier weight. They can also insulate their roots from the heat of the summer sun so that your tree does not overheat.
We recommend wooden planters made of sustainably-sourced UK Larch, it has a higher density and a large content of heartwood, which is denser, less permeable, and more durable than the surrounding sapwood. In addition, the structural properties of Larch are far superior to treated pine and are far better than any other available softwood.
Find out more about Wooden Tree Planters made of Larch >>
With their timeless style Terracotta pots are ideal to for Japanese maples. Terracotta’s porous nature allows for air and water to move through the walls, preventing soil disease and root rot which is perfect for Acers, particularly as theydo not like being waterlogged.
Plus, they’re timeless!
These planters are lightweight which is a great advantage if you need to move your Japanese maple tree to more protected areas during the winter.
The clay fibre bonding method creates a very strong substance. So, this means that these planters are strong, weatherproof and durable – a must for any outdoor planters.
Ironstone pots have a natural heavily textured finish a frostproof finish which is an excellent choice in both colour and strength. They are perfect as a centre piece for any traditional or contemporary garden and are ideal to display your specimen Japanese Maple.
Polystone and Fibrestone Planters
If you plan on long-term, container-growing your Japanese maple tree, as well as the planters mentioned above, then Polystone or Fibrestone is a material to embrace as they will certainly stand the test of time.
Polystone and Fibrestone is an extremely dense compound of resin and powdered stone that will stand up to the harshest of elements and look good all the while. It has the appearance of stone but whilst it retains a solid, heavy feel it is more manageable in weight.