It’s one of the most common challenges we hear about each spring: “I’ve got a block of ___________ (Early Robin, Skyler Rae, Orondo Ruby, Tieton, Regina, Benton – fill in the blank) cherries that I can’t get to set consistently.”
Planted for quality characteristics and harvest timing, these varieties can command high prices. But poor production has driven many orchardists to frustration, chainsaws, and grafters. Researchers studying the problem and growers who continue to nurture these blocks to profitability acknowledge it’s a battle.
“The limiting factor (in these varieties) is the short lifespan of the ovule,” said Dr. Matt Whiting of WSU. “In some cases you have just a very small window of opportunity to set fruit.”
That window is called the effective pollination period (EPP). EPP = Ovule viability time from bloom opening – (time for pollen adhesion + germination + tube growth down the style). In 2018, Whiting and his research partners Lu Zhang and Louise Ferguson found that at 64 degrees fahrenheit (near average bloom temperatures) ovules remained fully viable for 3-4 days in high productivity varieties like Rainier and Sweetheart, and only one day for low-productivity cultivars like Tieton and Benton. They decay from there. After 7 days with temperatures under 75 degrees, 80% of Rainier ovules were still viable, but only 30% remained so in Tieton, Benton and Sweetheart.
It takes at least 48 hours for any cherry pollen at any temperature to germinate and grow to fertilize the ovule. That’s why short-ovule receptivity, low-productivity varieties often set less than 10% of blossoms, while high productivity varieties can set as much as 70% of blossoms. It also helps explain why some cold springs (like 2022 when it snowed on bloom) result in better fruit set for low-productivity varieties. Low temperatures (Low 40s to mid 50s) extend ovule viability considerably and don’t slow pollen tube growth to the same extent.
Grower Strategies
So, when there’s only a short period of time to get pollen to the stigma, what options do you have? There’s no magic bullet, but we’ve worked with growers who’ve improved success rates by using some or all of these tools.
- Ensure pollinizer bloom quantity and overlap
- Place more bee hives in block
- Apply supplemental pollen repeatedly as bloom opens
- Spray plant growth regulator to buy just a little more ovule viability time (most effective in warm years)
Trial and Success in Orondo
Griggs Farms in Orondo has applied supplemental pollen to its Orondo Ruby blocks with electrostatic sprayers longer than just about any other grower. After experimenting with different rates and timing, they’ve refined their program the last few years and achieved good results and more consistent production.
“What we’ve had the most success with is having as many applications as we can as the bloom opens up,” said Sam Gwinn, a manager for Griggs. “We’re creating more pollination events closer to when the flowers open, just increasing the chances of actual pollination.”
Gwinn said field consultants have advised that there may be as little as 15-20 minutes to get pollen to the stigma in warm, windy years, “and obviously more time when it’s cooler.” They begin applying at 10-15% bloom, and then apply again as another 10% of bloom opens up to about 70%. In total, they’re aiming for six applications. With each application, they apply 15g/acre and drive every other row of their high-density, trellised plantings.
This year, all of those applications happened in two days. A warm-cool-warm weather pattern resulted in a near flash bloom with temperatures going from 40s to 70s overnight.
“We started really early in the morning and finished really late. We just kept going (as the bloom opened throughout the day),” Gwinn said. “We’ve had a lot of success spraying at night. We think it’s a little cooler, maybe a little moister.”
Although the weather conditions were very different, 2022 (snow on bloom) and 2024 (flash bloom in warmer temps) were two of Griggs’ best Orondo Ruby production years. The attention to fruit set and pollination is a strategic investment of time and money. Griggs doesn’t spray pollen on other cherry varieties that are highly productive without the extra expenditure.
Gwinn said they’ve tried and abandoned spraying ReTain and another plant growth regulator after seeing little impact, and also determined that pollen on beehive inserts wasn’t highly effective for Orondo Ruby. They have grafted more pollinizers into their orchards to provide additional pollen and hopefully set even more fruit.
Other Application Methods and Experimentation
A number of other Firman customers dust their short ovule receptivity cherry blocks with pollen. From what we’ve heard, the most successful approach mirrors Griggs’ experience in Orondo with applications each day – and sometimes multiple times a day – to cover the bloom as it opens. Some growers also add pollen to beehive inserts or mix in helicopter applications to improve their odds of setting more fruit.
We’ve planted our own Regina and Benton cherry blocks west of Yakima with the primary goal of harvesting blossoms and pollen. But, we also grow a cherry crop and use the blocks to try new pollen application ideas. Last spring, we hit our Regina bloom frequently with electrostatic spray application and also upped the amount of pollen in each tank. We’d seen some promise in higher rates in WSU trials and thought Regina might be the right place to try it again. The results were promising, and we’ll be experimenting this year to learn more.
It takes a ton of diligence, attention to detail, and sometimes a little luck with weather to pollinate financially viable crop volumes in these cherry varieties. We’re here to help and support growers however we can.
Research Reference
Zhang, Lu; Ferguson, Louise; Whiting, Matthew D. (2018). Temperature effects on pistil viability and fruit set in sweet cherry. Scientia Horticulturae, Volume 241 (18 November 2018), pages 8-17.
https://www.sciencedirect.com/science/article/abs/pii/S030442381830431X
