Gadenin日本語Get the appAcid soil is not optional
Sweet chestnut is a calcifuge: it will not thrive on limy ground. Aim for a soil pH between 5.0 and 6.5. On chalk or heavy lime the tree does not die outright, it simply stalls, yellows between the leaf veins year after year and never carries a useful crop. Test the soil before you dig the hole, not after the tree sulks for five seasons.
The second requirement is drainage. Chestnut roots run deep and hate standing water; a sandy or gravelly loam with depth to it suits them, heavy clay that stays wet through winter does not. Dig a hole a foot (30 cm) deep and fill it with water. If it has not drained away within about twelve hours, plant on a raised mound eighteen inches (45 cm) high instead of in the ground.
Give the tree full sun. Chestnut carries its flowers on the current season's growth in the outer canopy, so shaded branches make wood and nothing else. A young tree tucked behind a building will grow tall and thin reaching for light and start cropping years late.
Do not add lime, mushroom compost or wood ash to the planting area. All three raise pH, and on a chestnut that is the opposite of help.
How far apart, and how much room you are really giving away
A grafted chestnut on good ground makes a broad, heavy-limbed tree. Plan for the size it reaches at twenty years, not the whip you are holding. Trees planted too close shade each other out at the bottom, the lower limbs die back, and all the nuts end up in the top ten feet where you cannot reach them and cannot sweep beneath them.
You also need the ground under the tree to stay clear and walkable. The whole harvest is picked up off the floor, daily, for several weeks. Planting a chestnut over a rockery, a hedge bottom or a bramble patch means the nuts vanish into it. Mown grass or bare mulched soil under the full spread of the canopy is worth planning for now.
| Situation | Spacing between trees | Mature spread | Distance from buildings |
|---|---|---|---|
| Two trees in a garden | 30-40 ft (9-12 m) | 30-40 ft (9-12 m) | 40 ft (12 m) minimum |
| Small orchard row | 40 ft (12 m) | 35-45 ft (11-14 m) | 40 ft (12 m) minimum |
| Grafted tree kept pruned | 25-30 ft (7.6-9 m) | 25 ft (7.6 m) | 30 ft (9 m) minimum |
| Seedling tree, unpruned | 50 ft (15 m) | 50 ft (15 m) or more | 50 ft (15 m) |
Plant two, and plant them within pollen range
A single chestnut will flower, may set burrs, and will give you nothing but flat, papery shells. Chestnut is effectively self-incompatible and it is wind pollinated, so the pollen has to travel from one tree to another on the air. That puts a hard limit on how far apart the pair can stand.
Keep two trees within about 100 feet (30 m) of each other, and closer is better; at 200 feet (60 m) pollen transfer falls away sharply and the crop with it. If you can, set them on the upwind and downwind sides of the prevailing summer wind rather than across it, so the pollen is being carried toward the second tree during flowering.
The pair also has to flower at overlapping times. Two trees raised from different sources give you the best chance of that overlap; two suckers off the same parent are effectively the same tree and will not pollinate each other. If you only have room for one trunk, plant two trees in one wide hole three feet (90 cm) apart and let them grow as a twin-stemmed tree.
Putting the tree in the ground
Bare-root chestnuts go in during dormancy, from leaf fall until the buds swell, whenever the ground is neither frozen nor sodden. Container trees can go in whenever the ground is workable but still settle best planted dormant. Chestnut roots are brittle and resent drying, so get them into soil the day they arrive.
- Dig wide and shallow Make the hole two to three times as wide as the root spread and no deeper than the roots are long. Scuff the sides so they are rough rather than glazed. Roots move outward, not downward, in the first two years, and a wide hole is what they move into.
- Backfill with what you dug out Do not fill the hole with compost or fertilizer. A rich pocket in poor surroundings keeps the roots circling inside it. Break up the excavated soil, remove stones larger than a fist, and put it straight back.
- Keep the graft union clear On a grafted tree find the swollen kink low on the stem and set it four to six inches (10-15 cm) above the finished soil level. Buried, the scion roots and you lose whatever the rootstock was chosen for.
- Firm in layers and water heavily Add soil in three or four layers, heeling each one and shaking the stem so soil runs between the roots. Then water with at least five gallons (20 L) slowly, even in wet weather, to close the air pockets that kill bare-root trees.
- Stake low and mulch wide Drive a short stake at 45 degrees clear of the roots and tie low on the stem, so the top can flex. Mulch three inches (7.5 cm) deep out to three feet (90 cm) but keep the mulch two inches (5 cm) off the bark.
The first three years, and what to write down
Water a newly planted chestnut through its first two summers. Ten gallons (38 L) once a week in dry weather beats a daily sprinkle, because it wets the depth the roots are heading for. Keep a three-foot (90 cm) circle around the trunk free of grass; grass competes for water far more than most people expect, and a young chestnut in turf grows at half the rate of one in clean mulch.
Deer and rabbits browse young chestnut hard. A spiral guard on the stem and a mesh cage to four feet (1.2 m) saves the leader, and losing the leader in year two costs you a season of shape.
Write down, at planting: the date, where each tree came from, its position in the garden, and the soil pH you measured. Then each year note the date the catkins first show and the date the first burrs drop. Within three or four years those two dates tell you whether your pair actually overlaps in flowering, which is the single most useful thing you can know about a chestnut planting, and there is no way to reconstruct it afterwards from memory.