For the purpose of this page, we are interested only in that group known as Japanese Maples - or Japanese Acers. These normally fall in the group known as Acer palmatum - which is to say that the foliage is generally palm-like. (As in hand rather than palm trees!).
There is another group of the Acers which can rightly claim to be known
as Japanese maples. These are those Acers in the Acer japonicum
group. (japonicum = of Japanese origin).
Most of the shrubs - in either group - have good autumn colour foliage, and also attractive foliage for growing seasons. All are deciduous.
Foliage colour - Summer and Autumn - is determined to a great extent by the growing conditions regarding soil type and also the weather conditions.
The Acer family of trees - Japanese Maples -and shrubs is a wide ranging group. In terms of size, they can be anything from dwarf shrubs of just under a metre height, to largish trees with a height of 8-10 metres. Either as shrubs or trees, it is the foliage which is the attraction. Often attractive in the spring and summer, but it is the colour in the autumn for which they are really sought after.
Single leaf of Japanese Maple - Acer palmatum 'Dissectum' - showing seven distinct lobes, which are then further divided to put it into the 'Dissectum' group - Acer palmatum 'Dissectum'. This is the early Autumn colour of an otherwise light green leaf on Acer trees.
A point that is overlooked with the Acers group generally, is that there are several types that have variegated foliage. These though do not generally have the same Autumn colour effect as the non-variegated forms.
Spring is also a good time for Japanese Maple foliage colour. The colour of the purple forms in particular have a good Spring colour - at bud break and afterwards before the summer period. It is at this time of year that the foliage of Maples can be damaged, by late frosts and drying winds. the damage persist throughout the year on many.
Summer is also a period where Japanese Maples can suffer foliage damage from hot, scorching sun. This is often mistaken for being some type of disease. Not so - simply sun - or wind scorch - of the Acer foliage.
Acer japonicum and Acer palmatum originated in woodlands and forests. This important fact, gives us clues as to their general likes and dislikes. Because of their origins, Acer trees or shrubs are happiest in dappled shade, and growing in an organic type soil which is at the same time well drained. This applies to whether they are grown in containers or in the open ground. They will though, survive in most types of soil, but do better in soils of high organic content. This would have been natural in their native habitat.
Japanese Maples are admirable subjects for growing in good sized patio pots or other containers. A good organic potting compost with added soil and grit will normally be the best compost to use. The size of some varieties will be restricted by this method of growing - no problem here.
Advantages include the fact that the pot can be placed in a sheltered situation - avoid draughts from alleyways if on the patio. The pot can also be re-positioned in a sheltered place for hard winters, ready to be bought out on display in the spring though to autumn.
Foliage damage of Japanese Maple can result if the containerised Maple is placed in a position where it is likely to be brushed against. Damage can also be attributed to placing the container in an exposed., draughty position.
Add slow release fertilizer such as Osmocote at planting time, and then each spring. The shrub should not require any additional feeding throughout the summer months.
Watering will be required daily through the growing season if dry. Ensure that the soil does not become waterlogged through over watering or poor drainage.
Winter root damage can occur if the pot becomes iced-up for long periods. This can be prevented by 'lagging' the pot for the winter months, or simply by pacing other pots around in a tight cluster. Most patio pots - and Acers are no exception - will benefit from having a huddle of other pots throughout the winter.
Japanese maples often suffer from exposure to hot sunshine, where the delicate leaves are scorched. The same it true of draughty conditions. As the foliage of the Japanese Maples are the main attraction, it makes sense to protect the shrubs form extreme conditions in order to prevent foliage damage. They are generally slow in growth, so a damaged leaf is probably visible for the entire growing season - not being hidden by continues foliar growth. Basically, what you see during the first two months of growth, is what you get for the remainder of the season. Protect it.
There can often be a little bit of twig die-back after a hard winter. It is normally sufficient to simply cut out the dead growth before the growing season starts.
The Acer palmatum group of Japanese Maples have a wide range of colours and leaf forms. The colours can range from lime green, through to the deepest red or maroon bronze. Added to this, there are the varied leaf forms which add so much interest to these shrubs.
The basic leaf of the palmatum Japanese Maples, is -as its name suggests - palm-like, with normally five lobes or fingers, but can be as many as nine distinct leaf lobes. In many varieties, each leaf lobe can be further finely divided. This group is known as the Dissectum group of Japanese Maples - Acer palmatum 'Dissectum'.
In Japanese maples with either the basic or dissected foliage, there are then many varieties which have the wide range of leaf colours referred to above. There are also variegated leaved varieties. The common factor is, that they all have good autumn colour. The extent of the autumn colour can be determined by general growing conditions and soil types - as well as the preceding growing season.
The 'Dissectum' group of Acer japonicum are normally dwarfer in growth, and often with a domed habit. This makes them particularly suited to rock gardens and the like. In the context of a rock garden they can resample miniature Acer trees - rather than shrubs.
Left is a 'typical' Acer palmatum - showing the five-lobed individual leaves. Centre and Right shows the leaves of the 'Dissectum' group - being Acer palmatum 'Dissectum'. In this group, the leaves are still primarily five-lobed, but now each lobe is split into sometimes intricate dissected segments.
Left is the typical Acer palmatum 'Atropurpureum' - just starting its
autumn tints. Then there are images of a typical Acer palmatum 'Dissectum Atropurpurea' with the finely cut foliage.
Most Japanese maples have no problems for most of the time. Especially if given the right growing conditions as above. However, there are a range of pests and diseases that can be problematic. As usual, the pests are easier to deal with than the diseases.
Pests of Japanese Maples include sucking insects such as aphids and scale insects. Sometimes caterpillars and more rarely spider mites. The infestation by aphids is normally first noticed with a stickiness on the foliage - in advanced infestation it will have perhaps turned to sooty mould. Scale insects are a little more difficult to deal with than aphids. Whatever, there should be a swift response, for if the foliage is at risk, then so is the beauty of the plant - not to mention the overall effect on the plant's health.
Foliage can be damaged by foraging deer. Bark can be chewed by invading rabbits. Both pests should be dealt with as necessary. It will need exclusion, or other drastic action.
Diseases of Japanese Maples will include Coral Spot Disease, which is visible on the bark or - worse - the bare wood of the branch - normally as orange spots and growths. There is no chemical control available for this fungal infection. Cut out the affected growths and burn. It is normally a sign of a general malaise of the plant, so cultivation care needs to be looked at. One of the suspected causes is said to be pruning the shrubs in wet weather. This would include taking off the winter damaged sections in spring. Do this when the weather is DRY! Dieback and bare branches are usually the first sign of coral spot disease.
Leaf Tar spot is unsightly -but rarely has any detrimental effect. Pick off the affected leaves and destroy.
More serious is the disease of Honey Fungus. It normally leads to the death of the shrub.
Leaf scorch damage and wind damage should have been prevented. there is nothing you can do to repair the unsightly leaves! Likewise, late frosts can kill the young emerging leaves. Remove all and hope to see re-generation of new growths.
Japanese Maples should only be pruned if absolutely essential - but preferably not at all. If you must, then simply take out any dead or diseased wood - in DRY weather conditions - in the dormant late Autumn EARLY winter.
Seed propagation is possible with many varieties - if they set seed. It is best to collect the seed as soon as it is ripe, and sow in the open ground in similar conditions to the parent plant. Seedling emerge in the spring with luck (!), and can be carefully transplanted as soon as they have a few pairs of leaves. Water well a few hours before attempting to transplant.
Cuttings are difficult - but certainly not impossible. Softwood cuttings or semi-ripe cuttings can be used. It is normally the aftercare of the rooted cutting which are the most critical, and also getting them through the fist winter. (In a cold greenhouse or cold fame preferably).
varieties of Japanese Maples.
By David Hughes - email@example.com