High tunnel research bears fruit

Apples grow inside a high tunnel at the Fairbanks Experiment Farm.

The Fairbanks Experiment Farm will soon host an apple harvest inside two high-tunnel greenhouses.

The crop consists of red and green apples, some small and others the size of apples sold in local grocery stores. This is the second harvest for a research project developed by Cooperative Extension Service forestry specialist Bob Wheeler, who wanted to test the effect of unheated high tunnels on the survival rate and yield of apples, berries and other fruit trees in extreme cold conditions.

Wheeler died this summer. Meriam Karlsson, a SNRAS horticulture professor, and Kendra Calhoun, an Extension research technician, will continue his research.

Calhoun will soon pick, weigh and test the sugar content of apples grown inside and outside of two large plastic-covered high tunnels in a field opposite the Georgeson Botanical Garden on the UAF campus. Altogether, researchers are testing 39 apple varieties in the high tunnels, which measure 42 feet by 96 feet.

Calhoun helped erect the tunnels in May 2007 and she and two students with the Rural Alaska Honors Institute planted more than 200 trees two months later. The apple varieties tested are those known to grow in colder climates: Arctic Red, Carroll, Ukalskoje, and Golden Uralian, and others. The varieties were grafted onto rootstock of the Ranetka crabapple, which is known for its ability to withstand cold winters.

The continuing project is evaluating trees grown inside and outside of the high tunnels. Two weather stations and 10 micro-stations record environmental conditions hourly, including the soil and air temperatures inside and outside the tunnels, as well as soil moisture, wind speed, and solar radiation.

According to Calhoun, Wheeler did not expect much fruit until three years into the project. He was surprised when the trees fruited in their second year and delighted with the growth this year, she said.

Although the data for this year is not complete, Calhoun said it’s clear that trees inside the tunnel are blossoming and fruiting more than two weeks earlier than the other trees.

“The tunnels, obviously, are helping,” she said.

The end walls of the greenhouses are erected in mid-October to help preserve the heat inside the high tunnels. During winters, temperatures inside the greenhouse averaged 10-15 degrees higher than the outside temperatures, but soil temperatures were as much as 20 degrees colder inside, the result of the snow outside insulating the ground, she said.

Despite the colder soil temperatures, 80 percent of the trees grown inside the high tunnels survived both winters. Sixty-eight percent of the outside trees survived the first winter. After January 2009 temperatures dipped to nearly 50 below zero, only 45 percent of the outside trees survived the second winter.

Apple trees that died the first year were replaced with new seedlings the following year, except for the Asian pear, plum, and cherry trees, of which none survived.

A variety of berries was planted inside and outside the tunnels, including red and black currants, nagoonberry, and honey berry. The berries outside the tunnels had a higher survival overall than those planted within, which was not too surprising, according to Calhoun.

Calhoun and Karlsson hope to continue the work for at least another year. The project is funded by a grant from the Western Sustainable Agriculture Research and Education Program.

(Article provided by UAF Cooperative Extension Service communications office)

Further information:
"Fruit tree and berry crop trial program for Alaska Native rural communities in interior Alaska," UAF Cooperative Extension Service

Addendum: (Sept. 14, 2009)
"UAF sees sweet success in growing apples in Fairbanks," Fairbanks Daily News-Miner, by Jeff Richardson, Sept. 13, 2009