When planting your Japanese maple you need to begin by digging a hole approximately four times the width of the root mass of the plant. If you have gophers or other pests you will need to line your hole with chicken wire prior to planting. The ideal soil for Japanese maples is a slightly acidic (ph of 5.5-6.5) sandy loam soil with a low to medium amount of organic matter. Planting in this type of soil enables the root system to establish itself quickly. After digging your hole you should place approximately 50% - 70% of the original soil back into the hole when planting your tree (unless your soil is clay). The rest of the soil should be made up of Soil Mix or Super Soil, Compost, and Mulch. You'll also use a small amount of items such as Peat Moss, Gypsum, Soil Sulphur, and Coffee Grounds. (See Pacific Coast Maples soil formula/recipe at the bottom of this page).
In the Western states where the water is very hard it is recommended to amend your soil with gypsum. In heavy clay soils compost and Gypsum help condition the soil while increasing water retention. Sawdust or wood chipping should be used with care because as they breakdown, they use up the available soil nitrogen making it unavailable to your new tree. Your Japanese maple tree should never be planted to low into the ground. The top of the root ball should be planted even with ground. It is also important to have an oversized "water well" made of mounded dirt to keep the water from spilling over. Some landscapers prefer planting their tree an inch or two below the ground so that a more natural reservoir is formed rather than making a "water well" with mounded dirt.
If you are planting in heavy soils, such as clay, your hole should be much wider and not quite as deep to allow the root system to spread near and just above the natural ground level. The hole should then be mounded upward just barely up to the root collar, thus protecting the roots from drying out. If Japanese maples are planted too deeply in heavy soils, such as clay, it is like planting a tree in a large stone pot with no drainage. The tree will soon drown and die.
After planting place an inch or two of mulch around the tree (without touching the trunk) to keep the soil temperature moderated and conserve moisture. Japanese maples for the most part are very adaptable to soil types (except heavy clay soil). If you have clay soil, take out all of the clay and use the soil recipe provided below, in place of the clay. If you have a preferable soil type then use your soil as part of your soil recipe. If you have a preferable soil type then blend 50% - 70% of the soil you dug from the ground with the soil formula/recipe below. For example, if you use 70% of the soil from the hole you've dug then use the soil recipe below to make up the other 30% of your mixture. The soil dug from the hole must be mixed together with the soil recipe provided by Pacific Coast Maples. Obviously the better your soil is the more you'd want to use. If you live in Oregon your soil is fine, so just stick the tree in the ground. Japanese maples are not large feeders but should be fertilized in the spring, prior to the emergence of the new leaves, and one time in July. If you live in a climate that has warm temperatures throughout the year, you can wait to fertilize your maple one last time in September after the high temperatures begin to taper.
A newly planted Japanese maple needs several years before its relatively shallow root system is successfully established. Your maple should be kept weed free for the first few years, the competition for nutrients and water must be kept to a minumum. Newly transplanted Japanese maples need frequent watering to develop their roots. J.D. Vertrees, the leading authority on Japanese maples comments, "The uniform level of moisture supply, whether great or small, must be emphasized. I cannot stress the uniformity of watering too much. I do not imply the need for large amounts, but rather, constant amounts." According to a study done by the University of California, frequent watering in the first year of transplant is the single most effective thing you can do to increase your chance of success that the new plant will survive. With that said, the number one reason these maples die is from over-watering followed by over-fertilizing and placing them in an area where they receive too much direct sunlight. Please remember that Japanese maples are not deep-rooted trees so even older trees need frequent watering.
***Pacific Coast Maples has researched and come up with a soil formula/recipe we use on all of our maples in the nusery. Our recipe is used on all of our maples when planting in containers. The same formula is recommended when planting maples in the ground however We mix all of our soil in a 90 gallon composter so that everything is mixed up evenly, especially the Soil Sulfur. We use 10 gallons of Planter Mix or Super Soil (which can be purchased at Home Depot in large bags), 5 gallons of mulch, 5 gallons of compost, 3 gallons of Pumus or Perlite, 2 gallons of Peat Moss, 2 cups of Gypsum, 1 cup Soil Sulfur (no extra as this is strong stuff), 1 cup of coffee grounds. To measure everything we use a 5 gallon plastic bucket like you get at Home Depot. For example, for the 5 gallons of mulch we use 5 gallons or 1 full bucket. For the peat moss, for example, we fill the bucket 2/5 the way up the 5 gallon bucket to measure the 2 gallons. We recommend Pumus over Perlite because it is more attractive in the ground and does not float to the top and blow away in the wind like Perlite does. If you are using Perlite in the ground we'd recommend not using Perlite on the top layer so that the Perlite stays 6-8 inches below the ground's surface.We have come up with this formula because Japanese maples thrive in slightly acidic soils with a Ph of 5.5 - 6.5.