Hazelnut Pollination: Winter Flowering, Wind and Choosing a Partner

Two flowers on one bush, and neither looks like a flower

The catkins everyone recognizes are the male flowers. They form in late summer as short, stiff, green fingers, sit on the bush all through autumn, and then in the depths of winter they lengthen, soften and turn yellow, hanging three inches (7 cm) long and shedding clouds of pollen when the branch is knocked. That yellow dangling stage is the only part of the process that is easy to see.

The female flowers are almost invisible and this is why so many growers misdiagnose their bush. They are not separate structures on the twig but tiny tufts of bright red threads, about a sixteenth of an inch (1-2 mm) long, pushing out of what looks like an ordinary fat bud. You have to look along the twigs closely, ideally with the low winter sun behind you, to find them at all. Each of those red tufts, if fertilized, becomes one nut.

Both sexes occur on the same bush, which is exactly what misleads people into thinking a lone hazel should crop. It has all the parts. What it lacks is a compatible partner, because almost all hazels reject their own pollen and the pollen of their own clones.

If you cannot find the red female flowers in midwinter, it does not mean they are absent. On a bush with a heavy catkin display they are easy to miss entirely. Check several twigs at eye level on a bright, still day.

Wind does the work, and warmth does not

Hazel pollen is small, dry and carried on air currents. No insect is involved, and that changes the advice completely. A mild sunny spell during flowering, which would be a gift to an apple or a plum, does nothing whatever for a hazel. Do not judge a bad nut year by whether the weather was pleasant at flowering; judge it by whether it was windy, dry and whether the catkins and red flowers were open at the same time.

What genuinely helps is dry, breezy weather while the catkins are shedding. Rain washes pollen out of the air and glues catkins shut, so a long wet spell across the flowering window costs you nuts directly. Still, foggy weather is nearly as bad because the pollen never travels. A cold, dry, blustery week in midwinter is close to ideal, which is the opposite of what most growers expect.

Hard frost during flowering is the other risk. Fully open catkins and receptive female flowers are damaged below about 20F (-7C), and a severe freeze mid-flowering will take out that portion of the crop. The bush is not harmed and will crop normally the following year, so a single failed season after a hard winter is not a reason to change anything.

You can help along a small planting. On a dry, still day when the catkins are yellow and loose, cut a branch of shedding catkins from the partner plant and shake it firmly over the bush you want pollinated, or simply tap the partner's branches so the pollen lifts into the air. It is crude, it takes two minutes, and on a two-bush garden planting it measurably improves nut set.

Timing is the whole problem

The male and female flowers on a single hazel usually do not peak together, and the gap between different plants is wider still. One plant may shed all its pollen in early midwinter while another does not open a female flower until late winter, several weeks later. Those two will never pollinate each other no matter how close you plant them, and this is by far the commonest cause of a mature, healthy bush producing shells with nothing inside.

So the question to ask about a partner is not whether it is a different plant, but whether its catkins shed while your main bush's red flowers are showing. The female flowers stay receptive for a surprisingly long period, often several weeks, which gives you some tolerance, but the catkins shed for only a few days each. The pollen is the narrow window, not the stigma.

Diagnosing this in your own garden takes one winter of observation. Walk the planting once a week from early winter to early spring. For each plant, note the week catkins first look yellow and loose, the week they finish, and the week you first see red female flowers. Lay those observations side by side and the answer is immediately obvious: either the windows overlap or they do not.

If they do not, the fix is to add a third plant whose pollen shedding falls in the gap. Three plants from different sources almost always produce enough overlap to cover each other, which is why a nut plot is rarely planted with fewer than three.

1. Walk the bushes weekly through winter From early winter until the leaves start to break, check each plant once a week. It takes five minutes. Look for yellow, loosened catkins and for the tiny red threads emerging from fat buds along the twigs.
2. Log the two dates per plant Record the week pollen shedding starts and ends for each plant, and the week red female flowers first appear on each. Write the plant's position, not just its name, because suckers make plants hard to tell apart later.
3. Compare the windows Set the records side by side. If plant A sheds pollen while plant B is showing red flowers, that pair works. If every plant sheds pollen before any red flowers open, you have found the reason for your blank nuts.
4. Hand pollinate as a stopgap On a dry day, cut a shedding branch from the pollen donor and shake it hard over the receptive bush, or tap the branches to lift pollen into the air. Repeat on two or three separate days to cover the receptive period.
5. Plant to fill the gap Add a plant from a different source, positioned upwind and within 50 ft (15 m). Give it three to four years to reach flowering size before you judge whether the problem is solved.

How to tell pollination failure from everything else

At harvest, crack twenty nuts from the same bush and count. Full, crisp kernels mean pollination worked. Shells that are correctly formed but empty, or that hold a shriveled brown scrap, mean the flower was never fertilized. Neatly holed nuts are weevil, and split shells scattered under the bush are squirrel. Those three faults look nothing alike once you know what to look for, and treating a pollination failure with fertilizer or a spray wastes a year.

A float test scales this up. Tip the whole harvest into water: the empties float and the full nuts sink. If more than about a fifth floats on a bush that has cropped for several seasons, pollination is your limiting factor and a new partner plant is the answer.

Keep those counts alongside your flowering dates. Two or three seasons of records turn what feels like an unpredictable crop into a straightforward picture of which plant pollinates which, and that is knowledge you cannot buy or look up, because it depends entirely on the specific plants standing in your garden.