Large parts of the US have seen record rainfall this summer, and many gardeners are scrambling to adjust. Gardens thrive on balanced nutrition, sun, temperature, and irrigation, so too much water can cause as many problems as too little. For this blog, we’ll focus on the ways that heavy rain affects pollination. It’s a complex topic, so we’ll be presenting this as an executive summary and providing links to more detailed information about specific facets of the issue. So let’s dig in and learn about rain, pollination, and how they interact!
Rain Discourages Pollinators
As it turns out, bees and other pollinators don’t enjoy working in the rain. Heavy rain discourages pollinators from foraging; they’ll try to stay home and dry and if they must go out they’ll stick as close to their hive or nest as possible. Honey bees range out up to three miles under normal circumstances, so extended rainy conditions can put a big damper on pollination. For some garden plants like zucchini and other squash, this can lead to reduced fruit production or even no production at all. So if the rain won’t let up where you live and sunny days are few and far between, that might explain why your garden looks healthy but isn’t producing veggies for you.
Rain Disrupts Self-Pollination
Not all plants rely on pollinators. Some popular garden plants like tomatoes, peppers, and eggplants can self-pollinate, meaning that their flowers can pollinate themselves or other flowers on the same plant. This obviously makes things easier and makes pollination far more likely, but even self-pollination isn’t immune to the effects of heavy or extended rain. There are several different reasons for this. Contact with water, even rainwater, can destroy the viability of pollen and leave it unable to fertilize any flower at all. Heavy or ongoing rain also carries pollen away from the flower and down to the ground—gravity is a harsh mistress, as it turns out! Between the loss of pollen viability and the physical removal of the pollen from the flowers, rain can prevent self-pollination, too.
Rain Even Affects Hand Pollination!
We’ve discussed hand pollination previously, and it’s a great way to ensure that your garden plants get the pollination that they need or to selectively pollinate or cross-breed plants. Self-pollination can be especially great for indoor plants or conditions where pollinators are in short supply, making it a great tool for many urban gardeners. While hand pollination is really useful, it’s not invincible: hand pollination can be disrupted by rain, too. The mechanisms by which rain disrupts hand pollination are similar to the ways in which it disrupts self-pollination: pollen loses viability in the rain or just gets washed away before it can fertilize a plant. This can be endlessly frustrating for attentive gardeners, who brave the rain or time their pollination efforts during drier moments. So if you’ve been hand pollinating without the usual results, don’t blame yourself. Rain discourages both hand-pollination and—as with bees—hand pollinators.
Heavy Rain Can Damage Flowers
Veggie plants with larger flowers, like squash and zucchini, are especially prone to this. However, we’ve also noticed it with any flower that has large and delicate petals. Heavy rain can lead to early blossom drop as the petals and other tissues of the flower become saturated or damaged. Additionally, we’re told that too much moisture can prevent flowers from opening at all, which is especially bad for monoecious plants, IE plants with both male and female flowers like most squash species. The male flowers appear earlier and thus have more time to incur rain damage, meaning they’re unavailable when the female flowers (the ones that produce fruit) appear later on.
Rain Limits Oxygen in Soil?
We were a little surprised ourselves, but as it turns out there research to suggest that excess rain and over-saturated soils can disrupt plant respiration. We don’t normally think of plants as “breathing” through their underground structures—that’s part of what leaves do—but as it turns out soil and soil respiration are vital for plant health, too. It works something like this: plant roots absorb air as well as moisture and nutrition. Normally this isn’t an issue—most soil contains a fair amount of air trapped in small pockets dispersed throughout. However, excess rain both saturates and compacts the soil, which eliminates those small air pockets and the CO2 they contain. This disrupts root respiration and CO2 absorption to the plant, which has a negative effect on its health and ability to pollinate, fertilize, or even produce flowers. In addition, the loss of oxygen in the soil can harm the microorganisms that are vital for soil health, causing longer-term problems for many plants. It’s a complex issue—we don’t claim to understand it in full—and research is ongoing. But for now it appears that excess rain does affect plant/soil respiration in a negative way.
Helping Plants Cope With Excess Rain
So now that we’ve taken a look at how rain effects pollination and plant health, what can we do about it? Well, there are a few options. Transplanting plants into containers that offer good drainage can help, as can loosening soil either by hand or by incorporating soil amendments that help avoid compression and saturation. Patio gardens and container gardens may benefit from a bit of shelter, even just a tarp or garden cover placed over them to deflect some of the rain. The biggest tools we have are mental: adaptability, a willingness to learn from the experience, and the understanding that sometimes inclement weather happens. No matter the weather, we’ll get through it and try again next season. Gardening is a learning process tempered with a fair amount of faith so let’s keep learning and trust that this too shall pass.
Leave a comment