116 3rd St SE
Cedar Rapids, Iowa 52401
Fool’s Spring doesn’t easily trick Iowa trees into blooming early
Late-winter warmup does provide opportunity for pruning young trees
It may feel like spring — especially when compared with the below-zero temperatures of just a few weeks ago — but Iowa’s trees aren’t fooled.
“Native trees that have evolved to be here are used to this kind of weather,” said Carole Teator, program manager for ReLeaf Cedar Rapids.
With daytime temperatures this week predicted to reach the 50s and 60s in Iowa — and nighttime temps staying in the upper 30s in some parts of the state — some Iowans might be wondering whether their oaks, elms, maples and other deciduous trees are in danger of blooming early. When trees flower prematurely and then there’s a hard frost, they can lose the flowers. For fruit trees, no flowers means no fruit.
But two tree experts said they don’t see a big risk of that with the recent warm up.
“A lot has to do with soil temperature, rather than air temperature,” Teator said. “If we had several days in the 60s or 70s, then the soil temperature might warm up and we could have some real problems then if the temperatures plunge. (But) it's going to go back to the 30s and 40s. They'll be fine.”
Patrick O’Malley, a commercial horticulture field specialist with Iowa State University Extension and Outreach, said multiple factors determine when deciduous trees come out of dormancy.
Most Eastern Iowa trees need 800 or more “chill hours” between 32 and 45 degrees to break dormancy. Days when the temperature is below 32 degrees, like it was in early January, don’t count toward the total. Neither do days when nighttime temperatures are above 45 degrees.
The Corridor has between 400 and 500 chill hours this week, according to the Midwest Regional Climate Center at Purdue University.
“The bottom line is we are good for now, but for the rest of this month the less hours between 32 and 45 degrees Fahrenheit the better,” O’Malley said.
Once the threshold has been met, trees will wait to bud until the daytime and nighttime temperatures are consistently higher.
“The worst-case scenario would be to get several days of highs in the 70s and 80s in March and early April like we did in 2012,” O’Malley said. “This caused fruit trees to bloom in mid-April instead of the normal early May. Subsequently there were hard frosts in late April that wiped out most of the tree fruit crop in Iowa that year.”
Winter is the perfect time to prune deciduous trees because the branch architecture is more visible without leaves, Teator said. Oaks and elms should be trimmed only when the temperature is below 50 degrees.
Starting three years after planting, tree owners should make sure the tree has just one central leader, which is a branch that extends from the middle upward. If you see competing branches, prune them off, she said. Cross branches, which are branches that rub against each other, should be removed, as should branches with a “v” connection rather than a “u” connection.
“It's ideal to do the pruning when the branch is about finger size,” Teator said. “You never want to prune more than 25 percent of a tree in any given year.”
Get tree pruning tips
Cedar Rapids is posting tree pruning tips on its Facebook page.
Backyard Abundance and Sustainable Landscape Solutions will offer a hands-on course on pruning young shade trees from 1-2:30 p.m. Saturday at Wetherby Park in Iowa City. Virginia Hayes, a certified arborist, will teach the class that has a sliding fee from $5 to $30. Space is limited and registration is required on the Backyard Abundance website, BackyardAbundance.org.
Comments: (319) 339-3157; erin.jordan@thegazette.com
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