I am often asked about the culture of Japanese maples. Many customers come in asking about problems they are having with theri plants and more often than not, it is some kind of root issue. These maples are easy care, needing little extra attention beyond ample watering with good drainage and reasonably fertile soil A lot of people think their plants have some kind of disease with branches dying off irregularly, when the basic problem is just additional watering. Remember these plants come from monsoon regions, so ample water is necessary for good growth. Good drainage is also needed and occasional fertilizer availability. It is very important to keep the plant well hydrated during heat waves, and some shading from hot intense sun will be of benefit as well. Drying dessicating strong winds are to be avoided if possible, remembering that these plants are from forested / open woodland area, appreciating the association of other plant species for some shelter from extremes in weather.
Any reasonably good fertlie soil will grow a good maple, keep in mind good drainage, especially during winter. Exposure to sun, heat is also worth considering, they do not like intense heat, sun for prolonged periods. A tip here is that where a maple leafs out is how sun tolerant its leaves will be. For example, if the plant leafs out in full sun, it will be sun tolerant, and if it leafs out in fun shade, it will not(those leaves will burn if relocated to sunnier position). An extreme example is a plant growing in the central valley, those leaves will be very thick and almost leathery, strong to take any conditions from sun to shade since they leafed out in a hot and drier environment. However, that same cv. leafing out on the coast, in shade will have thinner, more tender leaves and those will dry and shrivel if the plant is moved to a sunnier, hotter location. Ample watering will help, but maples are somewhat particular about their leaves and where they open out.
Manhy people do not even consider applying additional water to help an ailing plant. Thinking about where the species originate will greatly assist in any cultural questions you may have. Think monsoon, many species come from these ample rainfall areas and also need good drainage. Often times a customer will think their tree has verticillium wilt since the branches die back in an irregular fashion. True, there is an obvious root issue going on, but with some further questioning to gather more information, I usually discover that the plant watering regime has changed and now their once healthy and beautiful tree is having problems… Additional watering is the first remedy I recommend before doing anything else. That usually solves the problem. Maples can get diseases, insect problems, but with obvious symtoms like that branch dying irregularly, a root issue is more than often the problem and easily corrected.
Soil for maples need not be extremely fertile. Any reasonably good soil will grow a good maple.
And poorer soils can have supplemental fertilizer applied to give better growth.
Shading for younger plants is recommended. They are more sensitive to climate extremes like intense hot sun. You will get better growth and appearance if you give some shade to young plants, especially during the heat of the day, hot afternoon sun.
Any all purpose fertilizer can be used for maples, a time release type is often convenient and will supply food to the plant for an extended period.

I prefer to apply fertilizer while maples are in a full flush of growth. There are plenty of actively growing feeder roots and leafy tops to absorb the fertlizer and promote perhaps a second flush of growth. I recommend using less than the recommended amount, but applied a little more frequently. A little goes a long way with maples. Too much can burn the roots. Watering the plants before fertilizer application is recommended and then watering in well that fertilizer after it has been applied is a good way to insure you will not burn the roots. Think of fertlizer as salt. (It is) and when you get some salt in a wound, it stings) well same thing for maples,,,, roots will burn if not well watered both in the plant and in the soil. And a well watered plant will disseminate that fertilizer well into the plant so it can be used to the utmost opportunity in the plant.
Pruning in summer. Well this is a large topic and I will give a few tips and answer the rest later. With vigorous shoots on a young plant, people often ask what should I prune off? I will answer back NOTHING! if you do not want a bigger tree, by all means prune off that ‘leggy’ shoot growth. But if you want your tree to reach maximum dimension at maturity, you do not prune those branches. Even though they look leggy now, they will branch and be more beautiful in the few years following. Just be patient and let the tree do its growing and they often shape themselves well with little or no attention to pruning, they do it all by themself! Now there are instances where a bit of small corrective pruning will be beneficial. Narrow crotch branches are to be avoided on all trees, shrubs, and pruning on of these branches back to be less dominant or removing altogether will benefit the eventual mature structural branching. To help conceal pruning cuts, I recommend this, prune vigorous shoots to a leaf above a leaf if you wish to have invisible pruning cuts later as that branch grows. You can save the more upright branch if you wish to add height (as in most weeping dissectums) or keep the outward branch if you wish to add width
on the more upright growers. Thkk of the mature dimension of the tree and that will be a good guide for you. Doubtless you will make mistakes, we all do and that is how you learn. Be conservative in what you prune, (remember, maples do not generally need much pruning at all)To widen a branch, prune to side by side leaves on vigorous shoots or to small side by side branches. This technique is useful to make a narrow branch wider, thus enjoying the leaves in a flatter, wider plane to be viewed.
Maples are a very large group, second only to orchids and within this big group, the Japanese maple group is very large, numbering over 1,000 cvs. and more come every year. To organize the huge number of cvs. available, they are grouped into similar growth types. There are dwarfs, spring color groups, variegatedsm dissectums(the very elegant weeping laceleaf types), cascading types(these often have larger leaves, elegantly and deeply cleft giving a very lacy effect to the texture of the plant and many also have a weeping, cascading canopy once some height is achieved in the juvenile growth stage, standard upright growers which can be very tall in some cvs. and the unusual group which serves as a catch all for the rest.
There is a maple for every landscape situation, need, and personal taste!