Gadenin日本語Get the appSite first: wind and afternoon sun do the damage
A Japanese maple has thin leaves with a large surface area and a shallow, fibrous root system that sits in the top foot (30 cm) of soil. That combination loses water faster than the roots can replace it whenever the air is hot and moving. The result is the crisp brown leaf margin that owners see in midsummer and mistake for a disease. It is not a disease. It is the site, and the site is what you are choosing now.
The two things that cause it are wind and direct sun in the hottest part of the day. Either alone is survivable; together they are not. A spot that gets sun until late morning and then falls into shade for the afternoon suits this tree almost anywhere it is grown. A spot that bakes from noon until evening, with an open aspect and nothing to slow the air, will scorch the tree every summer no matter how much you water.
Walk the garden at about two o'clock on a hot day rather than in the morning, because that is the hour that matters. Look for places in the lee of a wall, a hedge, a larger tree, or the house itself. A house wall that faces away from the afternoon sun is close to ideal: the wall breaks the wind, the shade arrives at the right time, and the ground stays cooler.
Reflected heat counts too. A tree planted against a light-colored wall or above a paved terrace takes heat from below and behind as well as above, and will scorch in a position that looks shaded on paper. Open lawn in the middle of a garden is the other common mistake, because the tree gets full exposure to wind from every direction.
| Position | Summer behavior | Verdict |
|---|---|---|
| Morning sun, afternoon shade, sheltered | Full color, no leaf burn | Best |
| Dappled shade under high tree canopy | Clean leaves, slightly softer autumn color | Very good |
| Full sun but completely wind sheltered | Some marginal browning in heat waves | Workable with mulch and water |
| Open lawn, wind from all sides | Brown margins by midsummer every year | Avoid |
| Above paving or against a bright wall in afternoon sun | Severe scorch, early leaf drop | Avoid |
| Deep shade all day | Thin growth, weak color, leggy shape | Avoid |
The soil this tree actually wants
Moist, well drained, and slightly acid, around pH 5.5 to 6.5. Those three words are usually recited together and each one is doing real work. Moist means the roots never dry out completely, because a Japanese maple has no deep taproot to fall back on. Well drained means water does not stand around those roots, which rot in waterlogged ground faster than most garden trees. Slightly acid keeps iron and manganese available; in strongly alkaline soil the leaves come out pale between the veins.
The way to hit all three is organic matter rather than sand or grit. Fork two or three bucketfuls of leaf mold or well rotted compost into an area about three feet (90 cm) across before you dig the hole, working it into the top eight inches (20 cm) rather than burying it deep. That improves both the water holding of a light soil and the drainage of a heavy one.
If your ground is heavy clay that stays wet in winter, do not try to fix it by digging a deeper hole and filling it with compost. That makes a sump. Plant on a low mound instead, raising the rootball three or four inches (8 to 10 cm) above the surrounding level and grading soil up to it. On chalky, strongly alkaline ground, a large pot is the more honest answer than years of trying to acidify a border.
Test the drainage before you commit. Dig a hole a foot (30 cm) deep, fill it with water, let it drain, then fill it again. If the second filling has not gone away within four hours, the spot is too wet for a Japanese maple planted at grade.
Getting the tree in the ground
Planting depth matters more than hole size. These roots want to be near the surface, and a maple set too deep sulks for years or slowly dies. The flare where the trunk widens into the roots should sit level with the surrounding soil, or a shade above it, never below.
- Soak the rootball first Stand the pot in a bucket of water until bubbles stop rising, usually fifteen to twenty minutes. A dry rootball planted into moist soil stays dry, because water moves around it rather than into it. This single step prevents a large share of first-year failures.
- Dig wide and shallow Make the hole two to three times the width of the rootball but no deeper than it. Loosen the sides with a fork if they have gone smooth and hard. The roots will spread sideways, so width is what buys you establishment, not depth.
- Tease out circling roots Rub the outside of the rootball with your fingers and pull any roots that are circling the pot out straight. Roots left circling will strangle the trunk years later. If the rootball is a solid mat, make three shallow vertical cuts down the sides with a knife.
- Backfill with the soil you dug out Use the native soil, improved with the organic matter you already forked into the wider area. Filling the hole with rich compost creates a container of soft material that roots refuse to leave. Firm gently with your hands, not your heel.
- Water in and mulch Water slowly with two full watering cans, letting it soak rather than run off. Then spread two to three inches (5 to 8 cm) of bark, leaf mold or compost over the whole planted area, keeping a clear gap of a couple of inches around the trunk itself.
- Stake only if you must A container grown maple usually needs no stake. If the site is exposed enough that the rootball rocks, use a short stake angled into the prevailing wind, tied low on the trunk, and take it off after one full growing season.
The first two summers
Until the roots have grown out into the surrounding ground, the tree is still effectively living in the volume of its old pot, and that volume dries out in a couple of hot days. Water thoroughly once or twice a week through the first two growing seasons rather than lightly every day, giving enough each time to wet the whole root zone. Frequent shallow watering keeps roots up at the surface where they are most vulnerable.
Do not feed at planting and do not feed for the first year. New roots grow toward moisture, not fertilizer, and a young maple pushed with nitrogen makes soft growth that scorches and dies back. The mulch supplies everything it needs.
Expect some leaf damage in the first summer even in a good position. A newly planted tree cannot yet supply the leaves it is carrying, and a browned margin on a few leaves in a first-year tree is not a verdict on the site. Judge the position properly in the second and third summers.
Write down what you planted and where
Record the planting date, the exact position, which way the tree faces, and how much sun that spot got at midday when you chose it. Note the leaf type as well, whether it is a broad-lobed form or one of the finely dissected ones, because the dissected kinds scorch far more readily and need the shadier half of any site you have.
Then, each summer, note the date you first see brown leaf margins, if any. Two or three years of that one date tells you whether the position is right, whether a dry spell caused it, or whether the tree is simply outgrowing the shelter that used to protect it. Without the record you will be guessing every year.