Suitable garden soils for a Japanese maple range from pure peat to chalk, limestone, heavy clay and everything in between. As I explain here, the alkalinity or otherwise of the soil is not the determining factor.
One of the many comments I get from visitors to my stand when I’m exhibiting at flower shows is ‘I can’t grow Japanese maples on my soil’ and it seems to be a common fallacy that they need an acid soil. The reasoning behind the assumption is they’ve grown a maple before and it’s died and they garden on chalk, lime or clay soils; therefore it’s the fault of the soil.
The maple family in general and Japanese maples, in particular, will tolerate any type of soil and are quite happy with a pH that ranges from 4.5 to 7.5. The lower limit will be when growing in pure peat without any added lime to counteract the acidity, right up to very alkaline soils based on chalk or limestone. The common denominator of all so-called problem soils is not the pH but rather their inability to hold moisture during the summer.
The only overriding requirement as far as soil type is concerned is that it is reasonably free-draining. Maples dislike having their roots in waterlogged soils, especially during the winter months when there is no root activity to reduce moisture levels and the root system runs the risk of being suffocated through lack of moisture movement. The end result of that scenario is the roots will rot and allow infection to spread through the plant.
To combat the problem of specific soil types not holding sufficient moisture in the summer, we come back to the need to mulch. This overcomes the perceived problem of growing Japanese maples in soils that, at first glance, seem inhospitable to their needs.
Water-logging in winter is often the cause of Japanese maples coming out in leaf in the spring, putting on a good display of foliage and then suddenly dying, often coinciding with strong winds or a slight frost. These events are then blamed for the demise of the plant whereas the real culprit has been water-logging and moisture stress. The tree still has some reserves of energy left in what remains of the roots and also in the body of the tree, which is why new growth starts out with such promise. Unfortunately, with little or no back-up it can’t sustain that growth, and the result is sudden death. Mulch to prevent stress in the summer and pick an area in your garden that has reasonable drainage and you remove at a stroke the main reason maples die.
Although frost can cause some damage in early spring just as the leaves are coming out, a healthy plant will continue to put out new growth and damaged leaves will have no long-term effect. There is, in fact, an easy way to differentiate between frost damage and root damage. If the tips of the shoots are blackened or burnt but the shoot is still generally firm, it’s frost. If the shoots droop and there is no firmness in them at all, then the damage is in the root system and the plant is going to die or is already dead.