It’s time to have The Talk. You know, about the birds and the bees…
That’s right, it’s time to talk about pollination in the garden. Without successful transfer of pollen between the male and female parts of the flower we won’t have any fruits or veggies to eat, and we also won’t have any new seeds to save and plant the following season. Out in nature, this process more or less handles itself, but in the garden we sometimes have to take matters into our own hands.
Animal and Insect Pollinators (Biotic)
Many plants and animals have developed mutually beneficial relationships allowing both species to thrive. The sweet nectar found in the flowers of many plants is a valuable food source for insects (entomophily), ants (hymenoptera), beetles (coleoptera), moths and butterflies (lepidoptera), flies (diptera), or birds and bats (zoophily). When these animals feed on the male flowers they brush against the anther (see Anatomy of a Flower) and pick up some of the sticky pollen in the process. Then when these same animals feed on a nearby female flower they will brush against the stigma and leave some of that pollen behind. Birds and bats, especially, will travel great distances to feed and can serve as fantastic delivery vehicles for plants that need to pollinate across great distances. Even in self-pollinating flowers just the act of an animal feeding can be enough agitation to release pollen within the flower for successful pollination.
The sweet smell of the nectar can be a strong attraction for many animals, but it isn’t always enough. The bright, bold colors and markings of many flowers are signals to certain pollinators and will attract them to the flower to feed. Flowers are also often shaped to accommodate certain feeders. Trumpet flowers offer nectar at the bottom of a long tube that can only be reached by birds with a long beak or butterflies with an extended proboscis. Other flowers are shaped with built-in landing pads to make it easy for flying insects to approach safely. It is in the plant’s best interest to make it as easy as possible for these pollinators to feed and gather as much pollen as possible to take to the next flower.
Wind, Water and Gravity Pollination (Abiotic)
Grasses are wind pollinated (anemophily), as are some trees and shrubs. Other plants may rely on water (hydrophily) or simply gravity to carry pollen. Pollination by the wind is very hit and miss. The wind may pick up pollen from a grass flower and scatter it all over the place, relying on chance that a little pollen land on another flower of the same species. To make up for this waste, wind-pollinated flowers produce a huge amount of pollen.
Abiotic pollinated flowers tend to have small dull-coloured petals or, in the case of grasses, no petals at all. They don’t need petals, color, nectar or scent to attract animals. The pollen grains are not sticky like those of animal-pollinated flowers, which reduces the chance of them sticking to leaves and other obstacles before they reach their intended target. The stigmas, on the other hand, are sticky in order to hold on to pollen carried by passing breezes.
Shake and Flick (self-pollinating flowers)
Hand pollination of a self-pollinating flower like peppers, tomatoes or egg plants is pretty straight forward. These are plants that have the male and female parts in the same flower and only need slight agitation to release some of the pollen from the anther to fall onto the stigma. When this agitation can’t be done by natural means (ie. wind, insect or animal activity) then it must be done by the gardener. The two easiest ways to do this are to gently shake the plant by one of the main stems or to gently flick the individual flowers with your finger. This gentle action should be enough to mimic the kind of disturbance the flowers would experience from natural forces.
Transfer (cross-pollinating flowers)
Cross-pollinating plants have separate male and female flowers and require the transfer of pollen from a male to a female flower for the successful development of seed-bearing fruit. In nature this is always done by a pollinator such as bees, butterflies, or some other animal. In a garden environment where these pollinators do not exist or are in short supply, we can do the work of transferring pollen ourselves.
Plants like cucumber, melon and squash are prime examples of common cross-pollinators in a typical garden. These plants will often produce male flowers first and continue to produce more male flowers than female flowers. Once your plant has produced a female flower you’ll want to watch for it to open, usually first thing in the morning. Once the female flower is open, we can hand-pollinate. Using a fine-haired, narrow paint brush or cotton swab, brush the anther of the male flower to collect the sticky pollen. Then gently dust the stigma of the female flower with the same brush to deliver as much of the pollen as you can.
If you find yourself without a brush, or don’t want to use one, you can pluck the male flower and remove it’s pedals to expose the stamen. Then you can brush the anther directly on the female’s stigma to transfer the pollen. This method works really well, but requires the removal and destruction of the male flower. So if you are trying to preserve the male flower for eating, it might make more sense to use the brush method.
Check out this short video to see some of the basics of hand pollination in action so you have a better understanding of how to accomplish this in the lab.