Kiwi Pollination: Male and Female Vines, Bloom Overlap and Hand Pollinating

Read the flowers before you diagnose anything else

Kiwi flowers are creamy white, about an inch and a half (4 cm) across, and open in late spring on the current season's shoots. Turn one over and look into the center. A female flower has a small green ovary sitting behind the petals with twenty to forty white sticky styles standing up from it like a shaving brush; it also has stamens, but their pollen is sterile, which is exactly why an isolated female fools people. A male flower has a dense yellow crowd of stamens and no ovary at all behind the petals.

This is worth doing in person on your own vines rather than trusting the label. If both your plants turn out to be female you will never get fruit, no matter how you feed, prune or pray. If both are male you will get flowers every year and never a single fruit. Either way the fix is to plant the missing sex, and every season you delay is a season lost.

A female flower that has been pollinated shows it within a week: the petals drop, the styles wither, and the ovary behind them visibly swells and starts to fuzz over. An unpollinated one drops off whole at the stalk.

How many males, and how close

One male vine supplies enough pollen for six to eight females, provided the females are close enough that bees and wind actually carry it. In a garden that usually means one male in the middle of the run rather than at one end. Pollen moves poorly beyond about thirty feet (9 m), and set falls off measurably on the vines furthest from the male.

If you only have room for two vines, plant one of each. If you have room for one, you have room for one that will never fruit, so either build more structure or graft a male shoot onto the female vine. Grafting a single male branch high into a female's framework is a legitimate solution in a tight garden, and it removes the distance problem entirely, but keep that branch clearly labeled or you will prune it out by accident one winter.

Bloom overlap is what usually fails

Having a male is not the same as having pollen on the day the female is receptive. Individual kiwi flowers are receptive for only about four to seven days, and the whole bloom on one vine lasts a week to ten days. If your male comes into flower a fortnight before the female, or a fortnight after, you have two healthy vines and no fruit, and the vines will look perfectly fine while it happens.

Check it by walking the vines every couple of days once buds start to fatten in late spring, and writing down the first day each vine opens flowers and the last day it has fresh ones. If the two windows barely touch, you have your answer. The remedies are to add a second male that flowers at a different time, to collect and store pollen from the early bloomer for use on the late one, or to hand pollinate across the gap.

Weather narrows the window further. Cool wet days during bloom keep bees at home and wash pollen off the styles; heat above about 90F (32C) shortens receptivity to a couple of days. A season with either extreme during that one week will give a light crop even on a well-matched pair, and that is not something you did wrong.

Getting insects to do the work

Kiwi flowers offer pollen but no nectar, which makes them a second-rate proposition for honeybees. If anything else nearby is in flower and offering nectar, bees will work that instead and walk straight past your vines. Commercial growers deal with this by saturating the block with hives; in a garden you deal with it by making the vines the most interesting thing available and by not spraying anything during bloom.

Two practical steps help. First, mow off or remove competing flowering weeds under and around the vines just before bloom starts, so there is less on offer at ground level. Second, do not use any insecticide, including so-called organic ones, from the time the first flower opens until the last petal falls; a single spray during that week can cost you the crop. Bumblebees work kiwi more willingly than honeybees, so anything that keeps bumblebees in the garden through spring is worth doing.

Hand pollinating, step by step

Hand pollination is straightforward and reliable, and on a small garden vine it takes half an hour a day for the week of bloom. It is worth doing whenever the male and female barely overlap, whenever bloom coincides with a cold wet spell, or simply when you want every flower to set a full-sized fruit.

1. Pick male flowers in the morning Collect newly opened male flowers on a dry morning once the dew has gone. Flowers that have been open two days have usually shed most of their pollen already. Take more than you think you need; each male flower will do perhaps five to ten female flowers.
2. Use the flower itself as the brush Pull the petals off a male flower to leave the stamen mass on a short handle, and dab it directly onto the white styles in the center of an open female flower. Roll it so pollen reaches styles all round, not just one side. This is faster and gentler than a paintbrush.
3. Or collect the pollen dry For a larger job, shake the anthers into a small dry container, leave them somewhere warm and dry overnight so they split, then sieve out the loose yellow pollen. Apply it with a soft brush or a cotton bud, or blow it onto the flowers with a puffer bottle.
4. Store surplus pollen cold Dry pollen in a sealed jar with a desiccant keeps for a week or two in the refrigerator and for a season in the freezer. This is the fix for a male that always flowers before your female: collect this year, freeze, and use it next spring.
5. Work the newly opened flowers each day Go over the vine every day or every second day through bloom, treating flowers that opened since your last pass. A flower is most receptive on its first two days. Marking each pass with a twist tie stops you covering the same shoots twice.
6. Check for set a week later Swollen, fuzzy ovaries with the petals gone mean it worked. Whole flowers dropping at the stalk mean the pollen did not take, and if that is widespread you should repeat the exercise on the next flush rather than waiting for next year.

The fruit tells you how well it went

Kiwi fruit size is driven directly by the number of seeds inside, and the number of seeds is driven by how much pollen reached the styles. A fully pollinated fruit carries well over a thousand seeds and grows to full size; a poorly pollinated one carries a few hundred, stays small, and is often lopsided, fat on the side that got pollen and pinched on the side that did not.

So cut a few fruits open at harvest and look. Small, misshapen, few-seeded fruit across the whole vine is a pollination verdict, not a feeding or watering one, and it tells you to fix the male, the overlap or your hand pollinating rather than reaching for fertilizer. Note that verdict alongside your bloom dates each year; after two or three seasons the pattern of which years set well and which did not will point straight at the cause.