Pollination in Greenhouse Gardening [Hometown Structures]

By far the most common question I get about growing vegetables in my Hometown Structures greenhouse is “but how do the plants get pollinated?” And as with most things in gardening, the answer just isn’t that straightforward. Of course, it is an important consideration when planning what you will grow in your greenhouse garden! The truth is, I don’t rely on pollinators in my greenhouse the same way that I do in my outdoor vegetable garden, and there’s a few reasons for this - as well as a few techniques I use instead to ensure my flowering plants are being manually pollinated by hand so they can produce the harvests I want them to. While there’s certain limitations in pollinating a greenhouse garden, most of them are easily overcome, allowing you to grow a wide variety of fruits and vegetables in your greenhouse with very little extra time and attention.

The role of pollinators

Without getting too science-y on you, pollinators play a crucial role in a garden by transferring pollen from the male part (stamen) of a flower to the female part (pistil). This process is essential for the fertilization of plants and the production of seeds and fruits. Pollinators ensure that plants can reproduce and continue to exist. A diverse population of pollinators supports a wide variety of plant species in a garden. Many of the fruits and vegetables we eat rely on pollinators for their production, and pollinators contribute to the overall health and balance of the ecosystem in a garden. Common pollinators in gardens include bees, butterflies, moths, hummingbirds, and bats. But of course, these creatures can have a difficult time finding and entering your greenhouse!

How do bugs pollinate plants in the garden?

Bugs have a few clever tricks to spread pollen from one flower to another. As they buzz around, pollen sticks to their furry bodies. When they visit another flower, some of this pollen can rub off, fertilizing the plant. Some bugs have long tongues that they use to suck nectar from flowers. As they do this, pollen can get stuck to their tongues and be transferred to other flowers. Other insects can vibrate their bodies to shake pollen loose from flowers. This helps to ensure that the pollen is spread effectively to many different plants.

How does pollination affect yield and fruit production?

When a pollinator successfully transfers pollen to the female part of a flower, it can lead to fertilization. Fertilization results in the development of seeds, which are essential for the reproduction of plants. In many cases, the development of seeds triggers the growth and maturation of fruits. These fruits often contain nutrients and are attractive to animals (including us humans!), which can help disperse the seeds. Without pollination, many plants would be unable to reproduce, leading to reduced yields and fewer fruits.

In a greenhouse, it is often a closed environment which pollinators cannot enter. Even in a backyard greenhouse with open windows and doors throughout the season, it is less likely that you will see a large population of pollinators inside, simply because it is not an organic environment or as much a part of the local ecosystem. While companion planting pollinator friendly varieties may help, we need to consider this when choosing what to plant and pick varieties that have self pollination features, or can be hand pollinated.

Which vegetable plants need pollination?

Many vegetable plants require pollination to produce fruit. However, this does not mean they need pollinators in order to do it, since many are what is called self-pollinating. Some common examples include anything in the Cucurbits family which includes squash, zucchini, pumpkins, cucumbers, and melons as well as the Solanaceae family of plants which includes tomatoes, peppers, eggplants. Legumes such as beans and peas and many fruits such as apples, berries, cherries, and peaches also require pollination.

How does biodiversity affect pollination?

A diverse ecosystem with a variety of plant species and pollinators can lead to more efficient and effective pollination. Some pollinators have evolved to specialize on particular plant species. A diverse ecosystem can support a wider range of specialized relationships, ensuring that more plants are pollinated. When multiple pollinators are available, they can visit more flowers, increasing the chances of successful pollination. It really is a numbers game! A diverse ecosystem is more resilient to disturbances, such as habitat loss or climate change, which can affect pollination rates. A diverse ecosystem can also support genetic diversity among plants, which can make them more resistant to pests and diseases.

What is self pollination?

Self-pollination occurs when pollen from a plant's own stamen (male part) is transferred to its own pistil (female part). This can happen in the same flower or between different flowers on the same plant. While self-pollination can ensure that a plant reproduces, it can also lead to inbreeding depression. This is when offspring inherit harmful genetic traits from both parents. To avoid inbreeding depression, many plants have evolved mechanisms to prevent self-pollination, such as having separate male and female flowers or releasing pollen at different times. However, self-pollination can be beneficial in certain situations, such as when pollinators are scarce or when a plant is isolated such as in a greenhouse.

What plants are capable of self pollination?

Many vegetable plants can self pollinate, making them a good choice for a greenhouse garden. Some examples include:

Tomatoes: While they can also be cross-pollinated by bees, tomatoes are primarily self-pollinating.

Peppers: Similar to tomatoes, peppers can self-pollinate, but cross-pollination can often lead to higher yields.

Eggplants: Eggplants are also self-pollinating plants.

Squash: Many varieties of squash, such as zucchini and yellow squash, are self-pollinating.

Cucumbers: While cucumbers are typically cross-pollinated, some varieties can self-pollinate.

Beans: Beans are self-pollinating plants.

Peas: Peas are also self-pollinating.

What is cross pollination?

Cross pollination occurs when pollen from one plant is transferred to the pistil of another different plant. Insects, birds, bats, and other animals can transport pollen from one plant to another as they gather nectar or pollen for food. Wind can carry pollen from one plant to another, especially in plants with small, lightweight pollen grains. In aquatic plants, pollen can be carried by water currents. Cross-pollination can lead to genetic diversity among offspring, as they inherit traits from both parents. This can make them more resistant to pests, diseases, and environmental changes.

How can you pollinate plants by hand in a greenhouse?

Pollinate greenhouse plants with hand pollination:

First differentiate between male and female flowers based on their structures. Male flowers typically have stamens (pollen-producing organs), while female flowers have pistils (ovary-containing organs). Gently touch the stamen of a male flower to the pistil of a female flower. This will transfer pollen grains, potentially leading to fertilization. Perform this process for multiple flowers to increase the chances of successful pollination.

Pollinate greenhouse plants with fans:

Place fans within the greenhouse to circulate air and disperse pollen. This can help simulate natural wind and increase the likelihood of pollen reaching different plants. Experiment with different fan speeds and placement to find the optimal conditions for pollen dispersal.

Pollinate greenhouse plants by shaking plants:

Gently shake or tap plants to dislodge pollen and facilitate its movement. This technique can be particularly effective for plants with dangling or pendulous flowers.

Pollinate greenhouse plants using a small paintbrush:

Gently brush a small paintbrush against the stamens of male flowers to collect pollen. Apply the pollen-laden paintbrush to the pistils of female flowers.

Timing pollination correctly successful fruit production.

Look for flowers that have fully opened and are displaying their reproductive organs. Some plants exhibit color changes in their flowers when they are ready for pollination. For example, tomato flowers often turn yellow.

Ensure that the plant is healthy and growing vigorously. A stressed or unhealthy plant may not be receptive to pollination. Provide the plant with sufficient nutrients to support flowering and fruiting.

Many plants have optimal temperature ranges for pollination. Research the specific requirements of your plant species. High humidity can promote fungal growth and interfere with pollination. Maintain adequate ventilation in your greenhouse or garden.

If you are relying on pollinators, monitor their activity around your plants. When you see them visiting flowers, it's a good sign that the plants are ready for pollination.

If you're unsure, try pollinating a few flowers at different stages of development to see what works best.

Looking for a high quality pre-made greenhouse in Massachusetts? Hometown Structures offers the finest craftsmanship with custom designs in a wide variety of sizes perfect for the home gardener to give your plants the perfect climate to thrive in a protected environment, keep pests away from your plants, grow plants and food that don’t otherwise exist in your area/climate and extend your season with options including 8mm twin wall polycarbonate for optimal insulation, venting and windows. Every custom shed greenhouse comes with 50-Year LP Siding and 30-Year Collapse From Snow Warranty.

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