One of the challenges of growing in an indoor aquaponics environment is that we don’t have nature’s pollinators available to us. But is this a big problem for most aquaponic gardeners? Pollination in aquaponics depends entirely on what you are growing. The only time that you need to worry about pollination is when you are growing a plant to harvest its fruit (e.g. tomatoes, cucumbers, melons, etc.) or if you are saving seeds and you need the non-fruiting plants to produce seeds.

Let’s start with a brief lesson on plant physiology and how pollination happens. Plant flowers actually contain reproductive parts known as ‘essential organs’. The male organ is called the ‘stamen’ and it is comprised of the long, stem-like ‘filament’ that is capped off with the ‘anther’ that contains the pollen. The female organ is called the ‘pistil’. At the top is the pollen receptacle called the ‘stigma’, followed by a tube called the ‘style’ which terminates in the ‘ovary’ which contains the eggs. Pollination is the act of getting the pollen from the male stamen into the female stigma so it can travel down the style and fertilize the eggs in the ovary. Flower petals attract insects to the flower which in turn unwittingly transfer the pollen (I’ll bet you are now realizing that this amazing plant sexuality is where the phrase ‘the birds and the bees’ comes from!).

But not all plant flowers are ‘complete’, i.e. not all plant flowers contain both male and female organs. In fact, horticulturalists divide plants into four pollination categories based on the location of their essential organs.

  1. Self-pollinating – Complete flowers that don’t need insects or wind to pollinate them. This group includes beans, peas and tomatoes. Vibrating or tapping the flowers of these plants will help with release the pollen and promote maximum fruit production.
  2. Requires pollen from an unrelated plant. The only vegetables in this category are cabbages and radishes, and pollination is only required if you are growing the plant for seed.
  3. Cross-pollination group. These make up the largest group and each plant has both male and female flowers. This group can be broken into two subgroups.
    1. Windblown pollen – Vegetables in this subgroup are sweet corn, beets, carrots and onions. Of these, only corn needs to be pollinated for food crop production as the corn kernels are actually seeds.
    2. Pollinated by insects – Some of these vegetables are self-pollinating, but the fruit set will be greater if insects visit the flower. Fruits and vegetables in this group include broccoli, collards, cauliflower, cucurbits (cucumber, cantaloupe, pumpkins and watermelon), okra, peppers and squash.
  4. Male and Female plants. The best examples are asparagus, spinach and some hybrid cucumbers. Again, pollination is only required if you are growing the plant for seed.

The bottom line is that unless you are growing plants to save their seeds, the only time that you will need to become actively involved in the transfer of pollen from the male organ to the female organ is with the Cross-Pollination group that is pollinated by insects (Group 3.2). And in this group the only fruits and vegetables that you can practically hand pollinate are the cucurbits (cucumber, cantaloupe, pumpkins and watermelon) because they have large flowers. How do you do this? Early in the day, while there is a lot of pollen on the flowers, follow these steps:

  1. Identify the male and female flowers. The female flowers have the stigma, which receives pollen, and the male ends have a stamen containing pollen. The pollen can be any color, including a light yellow, dark yellow or white.
  2. Touch the stamen of the male flower to make sure it is ready for pollination. If your finger has pollen on it, the stamen is ready.
  3. Touch the tip of the stamen, or the anthers, with a cotton swab, artist’s brush or your finger. Pollen should adhere to the swab. You can also remove the flower from the plant and fold the petals back, exposing the stamen.
  4. Transfer the pollen to the female flower’s sticky stigma.
  5. Repeat the process until you have pollinated as many of the flowers and plants as you desire.

Pollination in aquaponics is not a big deal, right? Especially if the result is a delicious melon or zucchini coming out of your greenhouse in the middle of winter!