Spring on track for Iowa trees, shrubs and flowers

"Right now, all of the apple trees still are quite dormant," said Paul Rasch, owner of Wilson's Orchard & Farm, in Solon. "We usually bloom that last week in April or first week in May, and that's really great for us if we can bloom later."

Spring is right on track in Iowa, with daffodils and tulips expected to bloom in early to mid-April, and fruit trees flowering a few weeks later, said Patrick O'Malley, a Linn County-based commercial fruit and vegetable field specialist with Iowa State University Extension.

A gradual warm-up is much better for trees, shrubs and flowers than the erratic swings in temperature Iowa often gets in the spring.

Trees and shrubs need between 1,000 and 2,000 "chill hours" between 32 and 40 degrees to go dormant in the winter.

After that, they wait for average temperatures to rise above 50 degrees to start flowering. So if we have a freak 70-degree day and 40 degree night in February, those trees think it's spring. When the inevitable March or April frost hits, trees could lose their fruit-making potential for the year.

"Any cooler-than-normal temperatures are good this time of year," O'Malley said. "A cold, cloudy day is great. That's one more day without having to worry about hard freezes down the road."

Rasch and Sara Goering bought Wilson's in 2009. Three years later, in 2012, a warm winter caused trees to come out of dormancy early and bloom in mid-March. Then April hit with some overnight freezing temperatures and most of the applies died.

"At Wilson's, where we normally harvest about a million apples, we had less than 1,000, probably a few hundred," Rasch said. "Every fruit grower east of the Rocky Mountains will remember that with angst."

Some large commercial growers use wind machines to mix warmer and cooler air to raise temperatures a few degrees to prevent an orchard freeze. That works for a night or two, but not when you've got a week or more of overnight frost, Rasch said.

Certain apple varieties serve as spring harbingers, he said.

"Ginger Gold ripens in late August, but it's always among our very first to get excited about flowering," he said.

Extreme weather — including hail, ice storms, floods, droughts and windstorms — are becoming more common in Iowa with climate change. For the agriculture industry, this might mean getting more crop insurance or changing planting dates. For Wilson's, it means more anxiety.

Wilson's plans to hold its second-annual Tulip Festival in late April and owners were a little worried when they saw shoots emerging earlier this month. Tulips have a three-week window and Wilson's didn't want the flowers to bloom before the festival.

"Last year, due to a cool April, it took about 40 days from sprouting to full bloom, but it could be as little as 20 with warmer weather," Wilson's posted on Facebook March 7. "We'll keep an eye out and keep updating as we get closer to nailing down a date for our second annual Tulip Festival!"

Then four inches of snow fell March 9-10, blanketing those early shoots.

Flower growers needn't be worried about that snow — it actually protects flowers, O'Malley said.

"The snow acts as insulation," he said. "If it's covering a plant, will keep it (the temperature) close to 32 degrees. If it gets to 20 degrees, the plant will still feel like 32."

If plants had already flowered and temperatures dipped below 28 degrees, there may be some damage, O'Malley said. But just having a few inches of leaves exposed to the snow will not hurt the plants. The next 10 days look great for flowers, shrubs and trees to bloom normally, he said.

That's good news for Rasch.

"Tulips are a very expensive crop to grow. You plant tens of thousands of bulbs per acre and then you're holding your breath and hoping the weather holds," he said. But the reward of seeing every shade of tulips blooming along Rapid Creek in the orchard last year was worth it. "It's quite a kaleidoscope."