Gadenin日本語Get the appTwo kinds of catkin on the same tree
In early to midsummer a chestnut hangs itself with long cream catkins and gives off a heavy, unmistakable scent. Look closely and there are two kinds. The bulk of them are purely male: a slender rope of stamen clusters and nothing else. A smaller number, usually further out toward the branch tip and appearing slightly later, are bisexual, with the same male stamens along most of their length and a few small green female flowers clustered at the base where the catkin joins the shoot.
Those green clusters at the base are the entire crop. Each one becomes a burr, and each burr holds one to three nuts. If you want to know in midsummer roughly what you are getting in autumn, count the bisexual catkins, not the total flower load. A tree smothered in catkins with almost no green bases at the bottom of them is a tree that will give you almost nothing.
The male flowers on a given tree usually shed their pollen before that tree's own female flowers become receptive. That timing gap is deliberate on the plant's part and it is why the tree standing on its own cannot rescue itself.
Wind carries the pollen, and not very far
Chestnut pollen is moved mainly by wind, with insects working the scented catkins as a secondary help. Wind pollination sounds like it should give unlimited range, but chestnut pollen is relatively heavy and it drops out of the air quickly. In practice the crop falls away fast with distance.
The practical rule is to keep pollinating partners within 100 feet (30 m). Inside 50 feet (15 m) you get a full set. Past 200 feet (60 m) you are relying on a windy week at exactly the right moment. A hedge, a wall or a building between the two trees also cuts transfer, because it takes the pollen out of the airstream at the height the flowers are at.
This is different from insect-pollinated fruit, where a bee will happily cross a quarter mile. Nobody is carrying chestnut pollen across your neighbor's garden for you. If your only possible partner tree is a chestnut two streets away, plan on planting your own second tree.
| Distance between trees | Typical nut fill | What you see in the burr |
|---|---|---|
| Under 50 ft (15 m) | Good | Two or three plump nuts, flat sides pressed together |
| 50-100 ft (15-30 m) | Usually adequate | One or two filled nuts, sometimes one blank alongside |
| 100-200 ft (30-60 m) | Poor and erratic | Mostly one small nut, the rest papery |
| Over 200 ft (60 m) | Effectively none | Burrs form and drop early, all shells flat |
| Single tree, no partner | None | Small burrs, thin flat shells with no kernel inside |
Reading a blank burr
Cut open a few burrs from the first drop rather than guessing. A properly pollinated nut is heavy for its size, filled hard to the shell, and its flat faces press against its neighbors in the burr. An unpollinated one is a thin, leathery envelope, often the full outline of a nut but weighing almost nothing, and it peels open dry with nothing but a shriveled thread inside.
Blanks caused by failed pollination are uniform: nearly every nut on the tree is flat, and the burrs themselves are undersized and drop earlier than usual. That pattern points at the pollination setup and nothing else. If instead you have plenty of good heavy nuts and a scatter of light ones, that is normal; the third nut in a crowded burr often aborts and no action is needed.
Two other things imitate a pollination failure. Drought during the weeks after flowering makes the tree shed burrs while their contents are still developing, and a hard drying wind during the flowering week itself can strip pollen before it lands. Both leave good years and bad years on the same pair of trees, whereas a genuine pollination problem gives you flat nuts every single season.
A burr that feels light in the hand before you open it is almost always empty. On a bad year you can sort most of the crop that way while you are still standing under the tree.
Fixing a tree that has no partner
The permanent answer is a second tree from a different source, planted within pollen range. It will take several years to start shedding useful quantities of pollen, so plant it as large as you can handle and keep it watered so it does not sit still for two seasons.
If you cannot plant another full tree, graft a second type onto two or three limbs of the existing one. Whip-and-tongue or cleft grafts made in late winter, while the buds are still dormant, take reasonably well on chestnut. Put the grafts high in the canopy and on branches pointing in different directions so pollen shed happens across the whole crown rather than on one side.
Hand pollination is not practical on a mature chestnut, which is a tall wind-pollinated tree carrying thousands of catkins. On a small young tree you can shake a cut flowering branch from another chestnut over the canopy on a still, dry morning while your own female flowers are receptive, and it does work, but it is a stopgap for one season, not a system.
Keep a flowering record for the pair
Because chestnut flowering runs over a few weeks and the male and female phases on one tree barely overlap, the only way to confirm your pair actually works is to watch them. Each summer note, for each tree, the date the male catkins first shed visible pollen when you flick them, and the date the little green female clusters at the catkin bases look glossy and receptive.
Three years of those notes tell you whether tree A sheds pollen while tree B is receptive. If the answer is no, no amount of feeding or pruning will produce nuts and you need a third tree flowering in the gap. Record the position of each tree with the notes too, because on a windy site which tree is upwind of which turns out to matter as much as the timing.