Acers are a large family of trees of varied appearance, many of which are very suitable as bonsai. They are a delicate deciduous tree with 5 pointed leaves born in pairs along the twigs, and with proper pruning they make the most wonderfull ramification with fine inner twigs and small leaves. If pruning and pinching is missed or done incorrectly the treee will still develop a fine outer silhouette but all the leaves will be on the very ends of the otherwise bare branches. This leads to a disappointing winter image but all is not lost as the tree will produce inner buds quite easily on bare branches.
An acer bonsai will give a wonderfull seasonal display, often with bright leaf colour in the spring, greens through the summer and autumn shades from yellow, through orange to red, followed by the bare winter image once the leaves fall off.
Acer Palmatum Beni maiko, 8 weeks between pictures. Notice the small pot in picture 1, then the tree was actually summer repotted gently to the larger pot to combat drying out.
A seed grown acer cannot be a named variety - even if it looks similar to a known tree. (This is due to the high likelyhood of cross polinating). A proper named variety will be grafted, or sometimes layered from a named parent plant. Many red leaved and feathery varieties do not make strong trees on their own roots and will always struggle as a bonsai in this form - these trees are best grafted to the stronger roots of a seed grown palmatum. As a tree matures the graft disappears and the bark matches up both sides - the tree above is a graft that is basically invisible now, having grown out over the last 60-70 years or so.
The desirable red varieties have pink or red spring leaves, fading to green for the summer. The easiest to find is Deshojo - a red tree that fades to a purple veined dark green. It tends to have a largish leaf and quite long nodes but makes a very nice and quite hardy red acer. Varieties like seigen, beni maiko, beni komachi have much brighter colours, smaller leaves and finer twigs - but it comes at a price, the trees are less hardy and need more care and protection, especially from late frosts, freezing winds and waterlogging.
Acer Palmatum sp. clump style
There are several natural dwarf acers - from the well known Kiyohime that has tiny leaves and masses of fine dense twigs, kotohime, yatsubusa, and the rarer Mikawa yatsubusa that has full sized leaves but growth extentions of barely 1cm. These varieties are not quite as easy to look after but the results as a bonsai are often worth the extra care. Kiyohime has a tendancy to be weak at the top and strong on the lower branches, a situation totally the opposite to other acers. For this reason you need to prune lower areas harder and be carefull with the top of the tree, or it will die out.
A 5 trunk clump kiyohime, originally part of Dan Bartons collection in 1982, imported from Japan as a semi specimen bonsai. 44" wide, 27" high, 28" oval pot - approx 70 yrs old. Last picture is Jan 2012, repotted to a shallower 28" oval and wired, thinned and prunned. Now the tree is 40" wide, 24" high but looks taller with the nicer silloette
Acer Palmatum Mikawa Yatsubusa
An old twin trunk tree imported to the UK in the early 90's.
This tree has a true 15 minutes of fame when bright red bud sheaths peel back to reveal lime green new leaves. Left unpruned it grows a huge 1cm a year ! but ends up so dense inner twigs are lost very quickly. This year I defoliated the tree for the first time in 15 years and many inner shoots have developed.
Potting, soil and repotting
The tree wants to be kept moist, especially in hot, dry windy weather otherwise the leaves will dry to a crispy brown on the edges ***and any chance of nice autumn colour is lost. Moisture though doesn't mean waterlogged! as this will kill your tree very quickly.
*** This leaf damage is also caused by mineral and lime biuld up in the leaf margins caused also by the tree starting to dry out on windy days***
The best way to get the moisture right is to use the correct soil - free draining to cope with the rain, but particles that hold water rather than let it all through. I use akadama, kanuma (the azalea soil) sphagnum moss and bark. Start with a layer of larger particles, then use a medium grade for the main potting and top off with a smaller grade of sieved akadama if you want to show the tree or encourage moss to grow. To get the best from a nice acer bonsai it is worth investing a little money in good soil, mixing potting compost and a handfull of grit is not ideal !
To ensure the tree gets the moisture it needs to keep the leaves perfect between watering the right size pot is essential- long shallow ovals (glazed or unglazed) look very good and the width of the pot means the soil underpins the branches with humidity. Shallow wide pots are much better than deep ones to avoid the waterlogging that will rot the roots, and if you use a similar soil mix to this one just the top layer needs to appear dry before you water. Then water properly until water runs out the drain holes, and it is a falacy that water on the leaves will burn them, I spray the leaves to keep the dust off and the pours unclogged. In fact i will spray the water over the leaves even on days when the soil doesn't need watering.
Repotting time is just as the buds are swelling, but before the leaves open. Then I usually cut back 1/3rd of the roots around the edge and a layer from the bottom. They cope perfectly well with root pruning if done at the right time. Also cut out large woody roots to encourage a dense pad of fine roots. Tie the tree into the pot with aluminium wire and fill all the gaps with soil properly, watering in well straight after. If you find the tree dries out in the summer adding moss to the surface will retain the moisture longer.
Pictures will follow when its the right time to take them
January 21st 2012---3pm !! - The buds are swelling and leaves are starting to open so time to get repotting the Kiyohime.
Have everything ready a few weeks early or you will miss the one or two day window to repot the tree. This is my new deciduous bonsai soil mix - it will hold loads of water to maintain humidity but will not stay waterlogged on wet days - it is a free draining mix that holds water !
35% supalight black
25% sieved akadama
10% - 5-10mm Bark
5% fresh chopped sphagnum moss
Putting specialist mixes together needs quite a few bags of ingredients - if you have just one tree that needs some new soil check the 'For Sale' page - this mix and the juniper and pine mix are on there in small quantities. Dont be tempted to mix potting compost and grit - many trees will rot in Cornwalls wet conditions, those that live just hang on to life and rarely respond strongly to bonsai techniques.
I'm using a shallower pot the same width so this is a 28" cream coloured oval made by china mist about 10 years ago. Potting mesh is secured to the holes and ALUMINIUM wire is threaded through to tie down the tree. Never use copper wire, and never use no wire at all !
Dont try and pull a good tree out of the pot - here i've used a sickle to cut round the root ball and remove a 1" slice. This allows the tree to be lifted from the pot with no damage and it cuts of the roots circling the pot in one go. Above we see the solid deep root ball, then it is washed with a powerfull hose, teased out with a root hook and trimmed with scissors.
Half the depth and a third of the width is removed - dont waste time trimming less than 1" off an acer as the inner rootball will compact so much it dies. repotting at the right time and with the right soil will not kill a healthy tree.
The tree is settled into the pot, lined up how you want it and the soil worked into the edges. Then you take the tie in wires under any nice surface roots and twist them tightly so the tree stays exactly where you want it in the pot. For a tree still being worked that is it, job done, if you are going to put the tree in a show I add a top dressing of sieved pure Akadama to the last 1/4 inch to give a neat even finish.
Water well and leave the tree to recover - as this is mid January we will need to watch for frosty nights and protect the buds and newly cut roots.
Pruning & Pinching
If left alone the tree will extend new growth tips with several pairs of leaves forming along the new shoot. As it hardens off inner buds will weaken and fine twigs will die off, leaving bare branches and poor ramification. If you are still devoping the tree let the new shoot extend then prune back to one pair of leaves. This will strengthen the branches and tree.
If you are refining the tree you need to wait until the first leaves are open then use a pair of tweezers to pinch out the shoot tip before it extends and opens any more leaves. This stops all extension of the branch lines and forces inner buds to open into new leaves. You cant leave it there though ! later in the summer the large outer leaves will shade the new inner growth so you need to reduce the outer leaf size or number to let in sunlight. Now the inner buds turn into small branches and the tree begins to look ramified and mature.
If your tree is healthy but suffering from poor inner ramification you can totally cut all the leaves off about 6-7 weeks after they have hardened off. This will force the tree to open many of the dormant buds all over the branches and even the trunk. Just doing this wont gain anything though, once the buds open you still need to pinch out the 2nd set of leaves from the branch ends to direct the energy to the inner twigs. Defoliating a tree will often lead to a much better autumn colour display too, but it can weaken a tree so dont do it every year. Red leaved varieties are reported to be weakened even more than other acers so be sure of the trees health and decide why you are planning to defoliate the tree. The Beni maiko above was defoliated following the first crop of leaves being damaged by hard late frosts in 2011 but it was a well kept healthy tree so it produced a full crop of new buds and leaves all over. I wont be contemplating doing it this year though.
A briliant short film that shows not only world class japanese maples, but also how to maintain them with spring pruning.