Gadenin日本語Get the appWhy fruit set fails without help
The flowers are monoecious: male and female flowers are separate but sit on the same plant, usually in the same drooping cluster, with the females fewer, slightly larger and carrying a small cluster of green pistils at the center instead of stamens. So a single plant has both sexes and, on paper, should be able to fruit alone. In practice it mostly does not. Pollen from a plant sets fruit poorly on that same plant, and every cutting or layer taken from it counts as the same plant.
On top of that, the flowers are not strongly attractive to the general run of garden pollinators. They are small, nodding, and hang under the evergreen canopy where insects have to work to find them. Even with two good genotypes side by side, insect visits alone often give a scattered, disappointing set. Hand pollination removes both problems at once and is the standard practice for anyone growing this vine for fruit rather than foliage.
The payoff is large and immediate. Vines that have never fruited in five years commonly set a full crop the first spring somebody works through the flowers with a brush.
Telling male from female flowers
Learn this once and the whole job takes minutes. Both types are cream to pale pink, bell-shaped and about half an inch (12 mm) across, hanging in loose clusters from the previous year's wood as new spring growth extends.
| Feature | Male flower | Female flower |
|---|---|---|
| Number per cluster | Many; the majority of what you see | Few, often one to three, sometimes none on a young plant |
| Size | Slightly smaller | Slightly larger and heavier |
| Center | A tight column of stamens shedding pale pollen | A small cluster of green, glossy pistils; no loose pollen |
| Stalk | Shorter and finer | Thicker, holding a visibly stouter bud |
| After opening | Drops within a few days | Persists; the base swells if pollinated |
Doing the job
Work in mid to late morning on a dry day, once the flowers have been open for a day or so and pollen is loose. Cool damp mornings and rain both ruin pollen viability, so pick your weather rather than your calendar.
- Collect pollen from plant A Pick two or three freshly opened male flowers from the first plant, or brush their centers with a small soft artist's brush or a cotton bud. You want visible pale dust on the brush. If nothing transfers, the flowers are either too young or still damp; come back in a few hours.
- Carry it to plant B Go straight to the second, genetically different plant and dab the pollen onto the green pistils of every open female flower you can reach. Touch each pistil in the cluster, not just the outside. A picked male flower can simply be pressed gently against the female center and used as its own brush.
- Reverse the direction Repeat in the other direction with fresh pollen from plant B onto the females of plant A. Use a second brush, or wipe the first one clean, so you are genuinely crossing rather than moving one plant's pollen around.
- Repeat over the flowering period Flowers open in waves over roughly two to three weeks. Go back every two or three days and work the newly opened females. Two or three passes usually cover the whole bloom period.
- Check for set a fortnight later Pollinated females hold on and the ovary behind the flower begins to swell and lengthen within about two weeks. Unpollinated ones yellow at the stalk and drop. Counting what stayed on tells you exactly how well the session worked.
When hand pollination still does not work
If a careful crossing session gives almost no set, work through the causes in order. The most likely by far is that the two plants are the same clone, bought from the same batch or propagated from one parent. Second most likely is that one plant produced no female flowers at all, which is common on young or heavily pruned vines, because the females sit on short spurs on older wood that hard pruning removes.
Third is timing: if the two plants flower a week or more apart, you can be collecting pollen when there are no receptive females anywhere. Male flowers can be picked and held for a day or two in a closed container in the fridge to bridge a short gap. Fourth is weather; a frost on open flowers, or a cold wet fortnight through the whole bloom, kills a season's set regardless of what you do.
Frost on flowers is worth planning against, because in mild-winter areas this vine often flowers early enough to be caught. A vine on a wall with overhead shelter, or covered with light row cover on a clear still night when frost is forecast, is protected cheaply.
Keep a simple pollination record: which plant gave pollen, which received it, the weather that morning, how many female flowers you treated, and how many were still holding two weeks later. Two seasons of that tells you your vines' real flowering overlap and how many passes you actually need, which no general guide can tell you.