Many backyard gardeners along the Front Range are facing disappointment this year, as they search in vain for the products of their labor among the leaves and vines. Many fruit-bearing plants, like tomatoes and cucumbers, seem to be growing well, and they might even be producing plenty of flowers this year. But that hasn’t translated into a robust harvest.
Where there are unfertilized flowers, there’s concern about pollinators. But entomologists say that to the extent this is a pollinator problem, it’s also — and foremost — a climate issue.
Different plants have unique anatomies, which makes for pollination processes with a lot of variation. So, while tomatoes and cucurbits — a family of plants that includes cucumbers, squash and melons — are all producing reduced crops this year, the reasons why are different for each type of plant.
Tomatoes
Tomatoes produce flowers that have both male and female parts contained within the same blossom, so fertilization doesn’t depend on pollen moving between flowers. But tomatoes do need help moving pollen within each blossom — from the male parts to the female parts of the flower, which can best be achieved through a process called “buzz pollination.”
Adrian Carper, a post doctoral researcher at University of Colorado Boulder who studies bees and plant evolutionary biology, says bumblebees are particularly well adapted to do this.
“Bumblebees are the great tomato pollinators,” Carper said, “because they hold on to the flower with their mandibles and they'll curl their abdomen under and then you'll hear … them buzzing their wings together and raining the pollen out, at a frequency that's targeted just to release the pollen from tomato plants.”
Carper says that a poor tomato crop could point to a disruption in the bumblebee population.
Bumblebee disruptions
Most people are familiar with honeybee hives and the large, perennial colonies they shelter. But bumblebees operate differently. Their nests are small — with colonies in the hundreds, rather than the thousands. Unlike honeybee hives, bumblebee nests are only designed to last one season.
“In the fall, all of that colony, except for the new queens that are made, will die,” Carper said, “And then the new queens actually find a little place to hole up over winter maybe under the eaves of your house or in your compost pile. And then they spend the winter there just basically kind of like asleep waiting on spring to come and then they'll emerge and start to build their own little nests or mini hives."
So, unlike honeybees, bumblebee queens start their nests from scratch each year, and it takes them time to build up a thriving nest of worker bees.
Last year the Front Range saw an early snow in October. Carper said that it probably killed lot of last season’s bumblebee queens, just as they were looking for a place to overwinter.
So, the Front Range started out with fewer queens this year. Then came a late and cold spring. The bumblebee queens woke up later than usual and got a late start building their nests and growing the first generation of worker bees. The mature bumblebee population ended up lagging behind the plants they pollinate.
And more weather…
Unusual climate patterns affected backyard gardens in more ways than one.
Cassey Anderson, a master gardener at Colorado State University Extension, pointed out that after the late spring, the Front Range saw an early summer, with a record-breaking string of days in the 90s.
“The flowers just aren't designed, like they didn't evolve to cope with high temperatures like that,” she said.
Cucumbers
Cucumbers are part of the cucurbit family, which also includes squash and melons. Cucurbit blossoms are either male or female — but they don’t have both parts contained within a single blossom. For pollination to happen, both male and female flowers need to be present at the same time.
Anderson says again, this year’s extreme heat is disrupting the normal processes of cucurbit plants.
“When they are stressed because of higher temperatures, they’re more likely to push male flowers, as opposed to male and female flowers,” she said.
According to Anderson, the plants are trying to conserve energy.
“If you think about it, pushing a flower out is a very energy intensive process for a plant,” she said. “And a male flower, it takes a lot less energy to push out than a female flower because the female flowers actually have that fruit at the base of the flower. So, if the plant doesn't have as much resources, if it's a little more stressed, it's much easier for it to throw a bunch of male flowers.”
Without a good balance between male and female flowers, cucurbit fruits can’t develop, no matter how healthy the pollinator population might be.
Agricultural differences
In spite of backyard garden woes, agriculture on the industrial scale is doing pretty well this year. Rocky Ford in southeastern Colorado is known for growing melons, which are also in the cucurbit family. They typically grow 4 million melons per season, and they’re doing well this year so far.
Michael Hirakata owns a 1,200-acre farm in Rocky Ford. He said a flower needs to get pollinated three times to get a good “set,” which means to make a nice fruit. As an agriculturalist, he has to be much more proactive — and scientific — about the plants he raises.
“We want to get the best yield we can, and we can’t leave a lot of this to chance,” he said.
Hirakata’s family has been growing melons in this region for over a century, and he has a lot of expertise. He explained that slightly drought-stressing plants is a good way to make them put on fruit. Hirakata Farms uses soil moisture sensors throughout the fields, and they are equally scientific about when — and how much — to fertilize the soil.
“You know, you got to treat it like your baby ‘cause cantaloupes are very, very fickle, I guess,” Hirakata said.
Gardening and farming are two very different pursuits, and what holds true for one is not necessarily the same for the other. Underlining this point, Hirakata, a master farmer, claims he can’t garden to save his life.
And yet… some good news
Despite all the challenges facing backyard gardeners this year, both Cassey Anderson and Adrian Carper are optimistic.
“I think there’s still hope for the season, especially with the cucurbit. They, if they're putting out any female flowers, those will continue to grow,” Anderson said.
And to help the tomatoes, Anderson has some practical advice: shade cloth. Although tomatoes usually like full sun, a little bit of shading can bring temperatures down to more tolerable levels for the plants. She recommends a 30% shade cloth, which are available at gardening or hardware stores. But, she also encourages improvisation.
“I actually have a master gardener who uses a lace tablecloth,” she said.
