Artificial "Asimina-lation": Pollinating the Paw Paw, N. America's Largest Fruit

As the redbud blossoms fade and dogwood flowers make their appearance, the mighty paw paw flowers waltz their way to center stage in the Ozark woodlands.

These luscious drooping maroon blossoms are sultry in their demeanor, but yet perhaps a little shy…

The paw paw has fast become a very dear tree to us, and we’re excited to get a little more intimate with some specimens this spring.

Immature Paw Paw Flower on the left, Mature on the right

Almost all fruit needs to pollinated to set fruit.

There are a few exceptions such as certain persimmons, which can set fruit parthenocarpically which results in seedless fruit. The same can be said about seedless watermelons. All other fruit require male and female sex organs to intermingle in order to produce fruit. While some trees are self-fertile (meaning one tree can pollinate itself), others require cross-pollination.

Generally fruits are either wind or insect pollinated.

The scope of fruit pollination is far beyond this article. Paw paws (Asimina triloba) are pollinated by insects and often need a little help with setting fruit. Being pollinated by flies and carrion beetles and having female organs that are receptive before the male organs shed pollen, proper pollination (and therefore fruit set) can be tricky.

Some old timers swear by hanging rotting meat to attract pollinators, but hand pollination seems like a more savory choice for most.

The paw paw flowers are known as perfect; meaning they contain both male and female reproductive parts.

The stigma (receptive female part) matures before the male anthers shed its pollen. Here lies the conundrum. To make things even more nuanced, the pollen must almost always (there are some exceptions) come from a different genetic source to ensure proper pollination. This is where is gets a bit frisky.

Today we are harvesting some paw paw pollen from the flowers of several different trees. Paw paws fruit best if cross-pollinated, that is by receiving pollen from another tree. It is recommended to plant at least 3 varieties for proper pollination, so we will be roaming the woods near us and collecting pollen in hopes of increasing fruit set on wild paw paws on our land. Our cultivated varieties have only 1 or two flowers so far.

Our goal is to transfer the male pollen to a clean and dry container and then transfer it to the female stigma. The pollen is ripe when the ball of anthers is brownish and sheds readily. The stigma is ready when the tips of the pistil are green, sticky and glossy. At this time the anthers ball is firm and light yellow to greenish in color.

Once we have collected enough pollen we will use a delicate brush and simply apply pollen to receptive stigmas.

This is a delicate task, but one that we feel is well worth the effort. For a tree that has few to no pests, does not require pruning in almost all cases and produces such a wonderful fruit, hand pollination seems a small price to pay.

Many of the larger scale growers, including the Kentucky State research facility report that pollination isn’t a problem.

Perhaps this is due to the large volume of flowers that creates a habitat for pollinators. The head of the KSU paw paw research team Sheri Crabtree, says that while hand pollination is the best option for optimum fruit set (as opposed to hanging rotting meat), she and her team say it isn’t needed in their paw paw test plots and orchards.

Playing sexy time with trees is fun, and hopefully will pay off in the form of scrumptious fruits in late summer. Artificial "asimina-lation" is a great way to connect with nature in a productive and intimate way.

Sources:

Paw Paw Fruit Facts

PAWPAW – A “TROPICAL” FRUIT FOR TEMPERATE CLIMATES

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