Welcome to the warmer zone: KC has more choices of plants

Gardeners, rejoice! New planting guide map opens up more choices of plants that usually thrive farther south.

01/26/2012 5:00 AM

05/16/2014 6:03 PM

It’s that almost-February time of year, when Kansas City gardeners begin plotting.

Hmmmmm. What to plant?

As of this week, they’re getting new advice from the federal government: A wider variety of species can safely grow here because the winters aren’t as harsh as they used to be.

Kansas City is now officially in the warmer planting Zone 6 instead of the cooler Zone 5.

That’s not news for the butterfly bush in your yard that used to die back almost to the ground every winter but now is hardly fazed.

Or the nandina that never used to flower in these parts but now produces gorgeous red berries like clusters of grapes.

Gardeners have understood for years that plants thriving south of here, say in balmy Oklahoma, are now comfortable at this latitude.

“You didn’t use to see much crepe myrtle around here and it was not offered much in garden centers,” said Dennis Patton, Johnson County Extension horticulture agent. “Now it’s a staple up here in Kansas City.”

The new color-coded map of plant hardiness zones is the first revision of the official guide since 1990. The zones are based on the coldest extremes in a given location — and those averages are not as cold as they used to be.

Kansas City’s old zone meant the coldest temperatures ranged from minus 10 to minus 20 degrees. Its new zone means the coldest it gets is between zero and minus 10.

“They try to take a snapshot of the past few years to look at what the normal low temperatures have been,” said Marlin Bates, a horticultural specialist with the University of Missouri Extension. “We know from plant physiology how much cold certain plants can tolerate.”

It’s a similar story over much of the country. Richard Primack, a Boston University biology professor, has a giant fig tree in his suburban yard.

“People don’t think of figs as something you can grow in the Boston area,” Primack said. “You can do it now.”

Passion flowers in Des Moines, anyone?

The new hardiness map arrives as Kansas City is enjoying an unusually mild winter.

The changes are too late to appear on the back of this year’s perennial seed packets, but the new map can be viewed at an interactive USDA website. The Arbor Day Foundation issued a zone revision in 2006 but the new, official USDA map uses more detailed factors and will carry more weight with gardeners.

In their own way, gardeners can be adventurous.

“We’ve all known we can get by with a little bit more than we used to over the last several years,” Patton said. “Gardeners always push their zone. That’s under the philosophy that you always want what you can’t have, whether it’s in the garden or it’s crème brulee for dessert.”

Nancy Branum of Gardner said the official switch in zones opens up new possibilities for gardeners.

“I’m a believer in trying new things,” said Branum, who has been a master gardener for more than 20 years. “That’s the fun of gardening.”

For example, she said she’d feel more comfortable now about planting Encore azaleas, a Zone 6 species that blooms more than once in a season.

Not every Zone 6 plant will survive here, she pointed out, but many are worth a chance.

The map change also means that more varieties of plants may be available in local stores, including some types of Japanese maples that have been rare to see for sale.

“It just opens the door for more diversity, which is what we need,” said Branum, a retired landscape designer.

At Powell Gardens, the new map will not create many changes.

The botanical garden already had experimented and found success with several Zone 6 varieties, including Encore azaleas and southern magnolia trees, said Alan Branhagen, director of horticulture. But the new map is a welcome clarification to Kansas City’s longtime planting dilemma.

It also will end a lot of questions, including one that came from an Illinois visitor to Powell Gardens who raised an eyebrow upon spotting a southern magnolia growing in Zone 5.

“I didn’t make the old map,” Branhagen told her.

He thinks the biggest winners will be beginning gardeners who “were losing out on a lot of neat stuff” because they probably strictly followed the old map.

Many independent nurseries had long ago adapted to the changes.

At Suburban Lawn and Garden, Matt Stueck said he agrees with the map’s new designation for Kansas City. But he cautions customers that the map is only one thing to consider. It hardly ensures that every Zone 6 plant will thrive here.

The map is meant to measure winter hardiness, but customers also should consider heat tolerance, he said.

“Cold temperature is only one of the factors. Wind and dryness are equally a factor,” Stueck said. “Something that doesn’t like clay soil and is a Zone 6 is really going to struggle.”

The 1990 map was based on temperatures from 1974 to 1986. The new map reflects temperatures from 1976 to 2005. The nation’s average temperature rose two-thirds of a degree between the two periods, according to the National Climatic Data Center.

USDA spokeswoman Kim Kaplan tried to distance the new zones from the issue of global warming. But David W. Wolfe, a professor of plant and soil ecology at Cornell University, said the map plainly reflects warming.

The new map “gives us a clear picture of the ‘new normal’ and will be an essential tool for gardeners, farmers and natural resource managers as they begin to cope with rapid climate change,” Wolfe said in an email.

For now, gardeners can take heart that the government’s hardiness map has caught up with what they see happening on — and in — the ground.

“We’ve said forever that Kansas City is in Zone 5,” Patton said. “I started to say in 2003 that Kansas City is in Zone 5 with increasing pockets of Zone 6 .... Now, pretty much everyone can grow Zone 6 plants. What’s probably going to happen is people in those old Zone 6 pockets are going to want to try Zone 7 plants.”

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