I would like to transplant a Japanese maple, probably 5 years old and about 8 feet tall. Can I do it in late October/November safely in St. Louis? And what is the best method?
Japanese maples are best transplanted when they are dormant—usually late fall through early spring if the ground does not freeze in your area.
The following information comes from Japanese Maples (by J.D. Vertrees, 2001, pp.61-62). This book also contains good information about mulching and general care:
When moving a plant to a different location within a garden, the plant must be dug with an earthen ball intact around the roots. If the plant is of any size or age, this root protection is important. It is also desirable that the planting hole be prepared in advance, ready to receive the plant with its root ball, as soon as it is dug up. Having the new planting hole ready minimizes the risk of the fine feeding roots drying out. For this reason it is imperative that, whatever method, material, or timing is used when planting a Japanese maple, the roots are not exposed to air or direct sunlight for any length of time. Such care will help prevent them from becoming desiccated, which would cause too much transplant shock and possible loss of the tree.
The planting hole should be dug slightly larger than the root mass of the plant. To enable the root system to establish itself quickly, it helps to mix with the soil organic compost, such as composted conifer bark mulch, rhododendron or azalea planting mix, or rose compost. In tight , heavy clay soils the compost helps condition the soil, while in light, sandy soils the compost assists in water retention. Sawdust or wood chippings should never be used as, during their breakdown, they use up the available soil nitrogen and render it unavailable to the newly planted tree.
The planting hole should be deep enough so that the root collar of the plant, the ground line at which the young plant was grown, is level with the ground surface. The exception to this rule applies to tight, heavy soils, like clay, where success will be greater if the hole is rather shallow so that the root system is partly above the ground level. When filling in the hole, the soil should then be mounded up to the root collar to protect the roots from drying out. If deep holes are dug in heavy soil, it is like planting the tree in a large iron kettle with no drainage. Surely the plant will soon drown and die.
Whatever the soil conditions, the tree should never be planted deeper than the root collar. After the first season or two, the plant will find the level of root activity at which it can exist in particular soil conditions. I have observed maples growing in some surprisingly dry, shallow, and exposed conditions.