Pawpaw – Pollination
Q: I heard you say on your radio show that a pawpaw is dioecious, having male flowers on one tree and female flowers on another. In fact, the flower is perfect or bisexual, not male and female.
A: I checked with native plant expert Theresa Schrum and she confirms what you say.
“Pollination can be a limiting factor in pawpaw fruit set. The flowers are protogynous, meaning that the stigma (the female receptive organ) ripens before the pollen, and is no longer receptive when the pollen is shed. Thus the flower is designed not to be self-pollinated.
“In addition, pawpaw trees are self-incompatible, usually requiring pollen from a genetically different tree in order to be fertilized.
“Finally, the natural pollinators of the pawpaw–various species of flies and beetles–are not efficient or dependable. Since they tend to form clonal colonies (one plant, many sprouts just like aspens), it’s difficult to receive pollen from an unrelated, yet close by pawpaw.
“Although it requires a little extra labor, hand pollination to ensure fruit set can be well worth the effort and can be done as follows: Using a small, flexible artist’s brush, transfer a quantity of fresh pollen from the anthers of the flower of one clone to the ripe stigma of the flower of another clone. Pollen is ripe when the little ball of anthers is brown in color, loose and friable; pollen grains appear as yellow dust on the brush hairs. The stigma is ripe when the tips of the pistils are green and glossy, and the anther ball is still hard and green. Do not overburden the tree with fruit, as this will stress the tree, resulting in smaller than normal fruit, and may cause limbs to break under excessive weight.”