The Japanese maple, Acer palmatum, is a small, attractive tree native to China, Korea and Japan. The tree likes the sun, can tolerate shade, and can be grown in containers or cultivated as bonsai. In the United States, the trees will thrive in growing zones 5 through 9, although they require heavy mulching to protect their roots in cold zones and shade or mulching in southern zones. They require little fertilizing.
To grow, the Japanese maple needs air and water as well as nitrogen and other nutrients.
Air and Water
Plants breathe through their roots. They need oxygen to grow. Heavy soils and clay are low in oxygen and so not good for Japanese maples. You can amend heavy soil and clay by working 10 percent to 20 percent of organic matter into it to help it get air and to drain. Use well-composted potting soil or mulch. Composted materials provide organic matter to the soil and help give it air. If you amend clay with freshly milled bark, micro organisms decaying the bark will eat the nitrogen your tree needs to grow. When you amend with materials that have not been decomposed, the pH of your soil quickly drops below the range necessary for Japanese maples to flourish. The soil pH measures the acidity or alkalinity of a soil. When you plant your Japanese maple, protect the root ball by putting soil around it, but not on top of it. You want air to reach the roots. Maples planted in clay or soil that's poorly drained can suffer root rot and disease. Amending it also increases drainage. You should plant your Japanese maple from 4 to 6 inches higher than clay or soil that drains poorly.
For a plant, the sun is a kind of nutrient or food. A Japanese maple will do best if it has sun in the morning and shade in the afternoon.
A Japanese maple ordinarily doesn’t need fertilizer. If you attempt to push its growth with fertilizers, you risk disease and stem dieback. Do not apply large amounts of nitrogen in the first or second year of growth. You can use a small amount of slow-release fertilizer in the late spring. Commercial fertilizers sold for Japanese maples are ordinarily 4-8-5. That means they have four parts by weight of nitrogen to eight parts of phosphorus and five parts of potassium. It is better to use half doses of inorganic fertilizers and modest amounts of water soluble fertilizers.
If you use pellets of fertilizers or so-called “spikes” containing nitrogen when you plant a Japanese maple, you can injure its roots. Granular fertilizers that you put on top of the soil often contain too much nitrogen and can damage your tree.