I get a lot of questions on culture for Japanese maples (Acer palmatum and related species group). One of the most important things you can do for your plants is to WATER them amply. Abundant water, and regularly available water are necessary for good growth. Good drainage is important as well, but most problems with these easy care plants is that the watering is less than their needs. Many inexperienced people often first think some kind of disease is affecting their plants. That may or not be true, and most often they observe dying branches as a result of verticillium wilt, but they do not even consider watering their plants more and consistently. Maples like water, but do not like to have wet feet(water logged roots). Almost any soil is suitable for good growth(they live in many soil types in the native range), but they all get ample water(think monsoon) and good drainage. So if you are having problems with growing your maples, first try an easy change in your care methods…water them more than you do. As long as excess water drains away, it should do no harm and you will see a healthier appearance of your plants and possibly more new growth(second growth flush in summer).
Fertilizing is recommended by some large growers, but if you soil is reasonably fertlie, only a small amount of supplemental fertilizing may be appreciate by your plants. Maples are not heavy feeders. And timing of the fertlizer application is important in your specific climate area. Seasoned maple growers will not fertlize their plants until in midsummer when there is active root and top growth. Watering the plant first to hydrate it is important, then apply the fertilizer (never use foliage fertilizers as they will burn the leaves), and then water the fertilizer in again after application. I prefer to use the ‘less is more’ technique, applying less than recommended on a more frequent basis. A little fertilizer goes a long way. Think of fertilizer as salt(which it is) and how a wound touched by salts stings you… the same with roots…. excess or dry plant roots burn with too much fertlizer salts.
Soil type should be well drained and include a generous amount of organic matter/humus/compost. In planting specimens in the ground, choose your site after a little consideration to drainage in winter and summer, sun exposure, soil type, irrigation availability, exposure to winds. Maples come from forested areas, open woodlands, so they appreciate the association of other plants nearby to help give them shelter and a break from the hot afternoon sun. Sun tolerance will greatly depend on where a maple opens its first leaves. If the plant leafs out in full sun, those leaves will be sun tolerant. If it leafs out in full shade, they will burn if moved to a sunnier location. new leaves will grow, but the appearance of the plant for that year will not be as good as it could be. Remember to water the plants in very well to settle the soil and plant slightly high or at grade of surrounding soil. Mulching is beneficial as well. just to not bury the crown of the plant too deeply. Of course, there are some varieties which are sun sensitive and will always need some shading, and those you will discover through experience either on your own or with an experienced maple grower. Some of the variegated dissectums and some spring color group cvs. like Bonfire, A. shirasawanmum Aureum, A. s. Autumn Moon, are examples of cvs. needing some degree of shading for best growth. Think of it like this… the maple treeleafs out in spring in a forested area. There are other plants leafing out at this time also, so there is full sun. As the leaves mature, they are partially shaded by those other plants and that gives the maple some partial shade. Some cvs. are sun sensitive, although many are tough trees that will take full sun. Location is a big determining factor. Plants in the central valley have much thicker leathery leaves than those grown in more coastal areas, and are able to stand high temperatures and full sun, but remember they leafed out in those conditions.
I am often asked about pruning maples…. to this I respond ‘what is the goal you are trying to achieve?’ Maples come in many different shapes and mature sizes. So careful consideration and thought before varietal selection will give you a plant that fits into your site w/o pruning at all, or at the most, only slight trimming/corrective pruning. Basic pruning knowledge is all that is needed, but maybe I should say, that is only the first starting point… The finer finesse of maple pruning will yield wonderful results. For example, if you wish to hide/make invisible, you maple trimming, you can try this. On a long branch, look for a leaf above and below a leaf on that stem. Pruning to just beyond that node will give you an invisible pruning cut in later years… That branching will encourage the direction of the branch to go up and down and you can select which growth you want to keep from that resulting new branching. For weeping cvs. most people would select the upward branch, and perhaps for an upright grower, the outer branch to give more width. Practise will help you to become more adept at pruning. (prune lightly, if at all, maples do not generally need much pruning at all if planted with ultimate mature dimensions in mind)
To widen a branch, prune to side by side leaves, or branches. That following growth will make the branch wider as it grows.
For most people, this aspect of pruning is too detailed, but it is here and available for any that wish to try.
An important consideration for new maple buyers is that they purchase a sapling tree, with new shoots growing all over the canopy, then they ask…. ‘what should I prune off of those branches?!’ NONE at the present time! Those straggly/leggy new branches will broaden out with some age and give you the mature dimension of the grown specimen! SO do NOT prune those off unless you want a small sized plant.
Among the vast number of cvs. available, maples are grouped together with cvs. of similar habits to organize the large number of cvs. There are dwarfs, dissectum(laceleaf), spring color, upright, cascading(upright young growth that weeps over with maturity). variegated, and the ‘unusual’ catagories.
The dwarf group are slow growers that take years to really develop into magnificent specimens. The grandeur of a fully grown large sized tree, only in miniature scale, often less than 10 ft tall at maturity. Very sculptural, and there are red and green forms. Spring color group includes some of the most brilliant types of smaller to medium sized mature specimens. New leaves unfold with bold colors, yellows, oranges, pinks, reds. Generally smaller leaves and they shape themselves up nicely w/o any pruning at all. Some are fully sun tolerant, others need some shading especially from hot afternon sun, heat.
Cascading group usually has very deeply cleft leaves, creating a lacy and elegant effect. Some of my favorites are included in this group. Red and green cvs. and generally brilliant fall colors.
Standard upright (and often larger growing cvs.) These are often very similar to the typical seedlings, plants found in the wild. Larger growing trees, and small to large leaves in reds, and greens, variegateds, etc. There are several other species and cvs. including hybrids which are grouped under the umbrella of ‘Japanese Maples’
Acer japonicum, A. sieboldianum, A. shirasawanum.
Maples are a very large group. There are numerous other species of interest, many are rare (like the stripebark/snakebark species), paperbarks, etc.