Our harsh winters dim hopes for 'u-plant' Christmas tree

  • Article by: CONNIE NELSON , Star Tribune
  • Updated: November 20, 2007 - 3:27 PM

A new growing method for transplantable, live trees has garnered headlines, but has yet to find advocates here.

Can I buy a live Christmas tree and plant it in the ground after the holidays?

"We get that question every year," said Robin Ostrander, nursery manager at Gerten Greenhouses in Inver Grove Heights. "People hear about it on TV and they want to try it."

This year, Ostrander and other garden-center workers are more likely to be peppered with that perennial holiday question because a new growing technique has been grabbing national headlines and raising eco-friendly hopes for a "greener" Christmas tree.

The technique, called pot-in-pot, involves growing Christmas trees in a lightweight, soilless mix in containers, which are buried in the ground. Because the roots are never cut (as they are with traditional field-dug or ball-and-burlap trees), container-grown trees develop healthier root systems, according to Pascal Nzokou, an assistant professor of forestry and Christmas tree production at Michigan State University. And that, in turn, seems to allow them to better withstand the move from outside to inside and back again.

So, can I buy a live pot-in-pot Christmas tree and plant it in ground after the holidays?

Uh, probably not.

Though pot-in-pot trees are being grown and sold as far north as Michigan (USDA Zone 5), local garden experts say our Zone 4 winters (with an average minimum temperature of minus 30 degrees) are still too harsh.

"It's not recommended here," said Mike Hibbard, horticultural adviser with Bachman's.

"We're just one zone too far north," said Ostrander. (Neither Bachman's nor Gertens are selling the trees this year.)

In addition, pot-in-pot trees require special care when grown in cold climates. They can't be exposed to bright sunlight or drafts and need to be watered frequently. More important, their stay indoors has to be brief.

"How long they can spend in your house is a big limitation," said Marsha Gray, executive director of the Michigan Christmas Tree Association.

Some pot-in-pot tree growers, such as Cathy Genovese of Candy Cane Christmas Tree Farm in Oxford, Mich., say the trees can be inside for as long as 10 days to two weeks. But Nzokou recommends that live trees spend as little as five to 10 days indoors before being taken back outside.

Here's why: Evergreens naturally go into dormancy in the fall. If they spend too much time in a warm, dry environment (such as a house), they can come out of dormancy. Then, if they're returned to the cold, they can suffer shock and die.

(Unfortunately, they can't stay inside until spring, either. "Our winters are too long, our houses too dry and our light levels too low," said Hibbard.)

Even after a brief stint in the house, container-grown trees can't be put in the ground until spring. Instead, they need to be stored in a protected place (such as an attached garage where the temperatures don't dip below 20 degrees) and watered occasionally so that they don't dry out.

Other green trees

Despite these limitations, live Christmas trees are becoming a hot holiday item. Already, Yule Tree farm in Aurora, Ore., (www.christmastreeoregon.com) has sold half its stock, even though the pot-in-pot trees cost more and are smaller than most cut trees. (This year, the company is selling its 4- to 5-foot container-grown trees for $109.)

"It's not going to be a 30-footer," said Joe Sharp, president of Yule Tree Farm, "but it's a real tree. It smells great, it looks great -- and it's alive."

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