Hand-pollination is used for flowers that are not self-pollinating when purity of seed is desired. The structure of the flowers and the genetics of the plant will determine how you hand-pollinate.
The first thing to know is that some flowers are self-compatible, some are self-incompatible but compatible with pollen from the same plant, and some are self-incompatible with any pollen of the same plant (referred to here as plant incompatible).
Some plants are considered self-compatible, meaning that the stamens (male part of the flower – contains pollen) in the flower can fertilize the pistil (female part) of the exact same flower. Some flowers are even created in such a way that the stamens will directly contact the pistil as the flower grows, matures, and opens. (These flowers are also called ‘self-pollinating’.)
This includes flowers of most beans, tomatoes, peppers, eggplants, etc. That means that flowers from these plants can be isolated, and then simply left alone until the fruit/vegetable is beginning to form.
However, to ensure good pollination, I give the plant a little shake, once a day, to make sure the pollen is getting moved from the stamens to the pistil. One year I had a tomato plant growing in a container on our apartment patio. There were simply no bees in the area, and even though the tomato flowers should automatically self-pollinate, the tomato plant was in flower for 2 or 3 weeks and none of the flowers were forming tomatoes.
I finally gave it a little shake and within 2 or 3 days, all the tomatoes began forming at once. So sometimes it’s a good idea, just to help the plant out.
Some flowers are self-incompatible, meaning the pistil of the flower will not accept pollen from the stamens within the same flower. It must be pollinated with pollen from a different flower in order to produce seeds.
Often pollen from a different flower on the same plant is adequate, but sometimes it requires pollen from a flower on an entirely different plant.
This technically falls under the ‘self-incompatible’ category, but I believe it deserves to be noted separately, to avoid confusion. Especially for new seed-savers.
Some plants produce flowers that are not only self-incompatible (the pistil won’t accept pollen from the stamens in the exact same flower) but they also won’t accept pollen from other flowers on the same plant.
This is the case with many of the brassicas, or the cabbage family, including broccoli, cabbage, cauliflower, turnips, radishes, etc.; and members of the umbelliferae family, including carrots, celery, dill, parsnips, fennel, etc.
Hand-Pollinating Different Types of Flowers
For plant-incompatible plants, it’s important to grow at least 2 or three plants of the same variety you want to save seeds from, isolate the plants, and then, using a camel-haired brush, transfer pollen from flowers on one plant to another and another, working on several flowers from more than one plant at the same time.
When a plant produces lots of little flowers (as the brassicas and members of the umbelliferae family do), using a large camel-hair brush, it is easy to gently brush across the flowers, back and forth a few times, working through each plant at least 2 or 3 times, to spread the pollen around.
Some plants produce a few larger flowers. With these flowers, use a small brush or a q-tip to move pollen from the stamens to the pistil.
When flowers contain both the male and female parts in the same flower, they’re called perfect flowers (members of the nightshade family, such as tomatoes, potatoes, peppers, etc. produce perfect flowers).
To ensure adequate pollination, hand-pollinate several flowers at once to move pollen from one flower to another on the same plant, or another plant of the exact same variety. Take care not to cross varieties.
Some plants produce the stamens in one flower and the pistil in another. These are called imperfect flowers. The most iconic example of this is the squash family.
In order to hand-pollinate flowers on these plants, you must isolate both a male flower and a female flower. When both flowers are fully-formed and mature, simply pull back or remove the petals on the male flower, and use it like a q-tip or brush to pollinate the female flowers.
For more information on specific garden vegetables and fruits, see “A Compendium for Seed Savers – Common & Unusual Garden Vegetables.”