This project focused on the feasibility of growing fruit in interior (urban and rural) Alaska using high tunnels. Fruit trees and berries were planted both inside and outside of high tunnel structures in Fairbanks, Alaska. Apples were primarily studied with the testing of 39 varieties. Climate, survival and harvest data were collected from the test site beginning in the summer of 2007 through the fall of 2010. These data will be used for developing publications to detail variety selection, production procedures and management, benefits of high tunnel technology in cold climates and the costs of growing fruit in the interior.
The objectives of this study were to:
-Establish a fruit tree trial in interior Alaska;
-Provide outreach and information to the public regarding fruit tree selection, planting, maintenance and winter management through various types of media (presentations, internet, email) and personal communication (in-person, phone consultations);
-Develop and maintain a website to provide information and results;
-Develop publications outlining:
*Apple varieties suitable for interior Alaska including selection, planting and care of trees.
*Applications and benefits of using high tunnels in interior Alaska, procedures for construction, basic high tunnel production approach and techniques
In 2007, the Alaska Division of Agriculture, Department of Natural Resources reported that Alaskans spent 2.6 billion dollars on food. Only 1.3 percent, however, was spent on Alaskan agricultural products. Factors contributing to this small percentage include Alaska’s current economy, the lack of an agricultural infrastructure and food choices. Alaska largely depends on outside sources of food, which increases the cost and types of food readily available.
Rural Alaskan communities are particularly affected as food cost may be double or triple compared to urban areas (Fried 2010). These, often very remote, communities are vulnerable since they are dependent on food imports to sustain dietary needs. While subsistence is still prominent in most Alaskan native communities, large amounts of food are brought in at increasing and fluctuating expense (Fried 2010). Transportation and fuel costs directly impact food choices. As fuel prices are increasing, these communities are forced to make adjustments and are searching for more cost effective food alternatives.
In addition to the issues of high food costs in interior Alaska, nutrition and general health habits are also of increasing concern. The food available in rural communities is not always the most desirable or nutritiously beneficial. Diabetes and obesity are particularly on the rise in rural Alaska and the need for affordable healthy food options is essential (Alaska Department of Health and Social Services 2010a,b).
This study was initiated to test the feasibility of growing fruit in interior Alaska. High tunnel technology has been developed to improve and extend field productivity beyond the normal growing season. Taking advantage of recent season extension advances, we aimed to prove that fruit may be grown in the harsh environment of Alaska at reasonable cost. Fairbanks was used as the test site since the climate is similar to many interior villages.
It is our hope that the results of this trial will provide baseline data for urban as well as rural communities throughout the interior to consider growing fruit trees. We also hope to inspire communities to experiment with high tunnel technology to grow various food crops to offset rising food costs and provide some level of sustainability.
The study was conducted on the Fairbanks Experiment Farm at the University of Alaska, Fairbanks (UAF, Figure 1). This site was chosen because of its proximity to UAF and similarities in climatic conditions to many interior villages (Table 1).
The high tunnels were orientated north-south based on prevailing wind patterns, soil drainage, sun exposure and preexisting tunnels next to the site (Figure 2). Soil samples were taken in early spring directly after thaw. Based on the soil analyses, little mitigation was necessary before planting.
Two high tunnels (42 X 96 feet, Clear Span, FarmTek, Dyersville, Iowa) were assembled and constructed on the site according to the instructions from the manufacturer. The high tunnels were outlined and post holes (25 along each side and along the center) were dug using a power auger. Sides were squared and leveled, and the posts were pounded in and re-leveled as needed. Once the posts were in place the arches (rafters) were assembled.
In addition to the supplies included with the tunnels, the arch assembly required:
-A large relatively flat surface
-A power drill
-Several titanium drill bits (to fit 1” tek screws)
Each arch was made of five separate pieces. The arches were assembled in two parts; two or three pipe pieces were assembled and fastened with one tek screw per pipe. Arches were moved directly to the site using a forklift. We used a boom truck to assemble the arches, with one worker in the basket joining the arch pieces and securing the centerpiece with the supplied coupler. The purlins were added at the same time on either side using the boom truck on one side and a hay wagon with ladders on the other. Purlins were kept as straight as possible. About four people total were needed to place the arches and secure them into the ground posts. Once the structures were complete, we anchored them in with duckbills (Size 88, 12 inch body with screw ends) and crescents (two feet). We used three duckbills and one crescent on each side and two cable tie downs along the center (Figure 2).
Once the structures were secured, the plastic coverings had to be installed. This involved several people (at least six) and plenty of rope. We chose a relatively light- to no-wind day. We laid the plastic out on one side of the tunnel and inserted conduit as instructed in the manual, tying ropes to the conduit along the length of the plastic. The ropes were then hoisted over the tunnel frame and pulled from the other side until the entire structure was covered and the plastic was centered over the structure. We then added the rest of the conduit pieces and strapped the cover in place with the supplied straps and large ratchets that were attached to the inside of the rafters. This process was repeated for the second tunnel (please refer to our website for more details and photos of the construction http://www.uaf.edu/ces/ah/fruit-tree-trials/).
With the covers secured, we then installed the roll-up side devices. The supplied gearboxes were not strong enough for the 96-foot length, 7.5oz plastic mesh covering. Larger boxes had to be obtained from FarmTek and these did not work that well either. For the duration of the trial, sidewalls for the most part were manually moved when needed.
The tension on the covering material was adjusted daily for the first few weeks to ensure the structure remained straight. The area inside the tunnels was tilled and rowed (six, 12 inch rows/tunnel). The same was done to the exterior plots (Figure 3).
All trees were obtained from Dan Elliott Nursery in Wasilla, Alaska. Trees were grafted using Ranetka rootstock and a total of thirty-nine varieties were planted (Table 2). Tree varieties were selected based on their cold hardiness and on successful trials of varieties conducted in Alaska and Canada. Each tunnel and plot was planted with 60 trees spaced either six feet apart and six feet in-between rows or seven feet apart and 12 feet in-between rows. Two Cherry trees were also planted inside one of the tunnels.
Trees were planted in July. Holes were dug manually and were twice the width and depth of the root base. Holes were watered and a teaspoon of low-nitrogen start-up fertilizer was added to two gallons of water that was used to water the plants in once placed in the holes. Risse’s Triple R topsoil was added on top (also very low N containing). Small burms were made within two feet of the each tree, in a circular manner to retain watering and collect rainfall. The trees were not pruned the first season and fertilizer was not applied (Figure 4).
The trees were fertilized early each season (no later than mid-June) with 113 – 226 grams of a low-nitrogen, organic fertilizer (Fox Farms, Peace of Mind, All Purpose Organic Fertilizer (5-5-5)). Trees were pruned of rootstock when needed. Data were collected on tree survival each spring, and flowering and fruiting were monitored throughout the summer. Apples were harvested and measured for sugar concentration at the end of each season.
Trees were watered manually the first season. Each tree received two gallons of water twice weekly during the growing season and once weekly starting in August. Exterior plots were watered less when there was rainfall. Drip irrigation was set up before the second season, and each tree received three-four gallons per watering throughout the growing season, depending on the air temperature. Trees were watered more when there was little precipitation.
Tunnels and plots were weeded daily by hand and roto-tilled once a week. To keep weeds down around plots and tunnels, the entire site was tilled once a month with a tractor. Extra care was taken to keep the area around the trees weed-free. No chemicals were used at any time. It was particularly difficult to keep the tunnel edges and sides weed-free since rainfall run-off in these areas was common. A weed-wacker was used to keep weeds along the fence line down and, later in the growing season, along the edges of the high tunnels.
In preparation for winter, at the end of each growing season, watering was reduced starting in September to every other week. Care was taken to ensure that the trees were well-watered before freeze up.
Tunnels (2007 – 2010)
At the end of each season, the end walls were installed (typically in mid-October). The trees inside the tunnels were covered with 1 m x 1 m pieces of reflective insulation and covered with straw (12 inches) along with tubex or treepee tree covers in 2007 only (Figure 5). Six mil (0.15 mm) greenhouse plastic was added as needed primarily to the sides and corners of the tunnels. Duct tape and Tyvek tape were used to secure the plastic (later, nylon rope and cable ties were found to be more durable and effective).
Trees (2007 – 2010)
The trees were fitted with spiral tree guards to prevent vole damage and were pruned of rootstock if necessary. No other preparations were made to the trees.
Ten HOBO microstations, five inside a tunnel, five in an exterior plot, were placed on random trees measuring;
-Air temp and RH
-Soil temp between 5 and 10 inches
Two HOBO weather stations were set up inside a tunnel and in one exterior plot.
These were set up to measure:
-Air temperature and relative humidity
-Soil temperature at 5 and 10 inches depth
-Photosynthetic active radiation (PAR)
Data loggers were set to take measurements hourly throughout the growing season and winter for each year. Batteries were changed yearly and data were usually collected monthly throughout the growing season and in the spring after each winter (Figure 6).
- Radiation shield, set up and close up of microstation in the winter.
- Figure 3
- Newly planted trees inside a high tunnel and outside.
- High tunnels and exterior plots in the winter and inside a tunnel with trees prepared for the winter.
- Figure 1 and Table 1; Site location and climate data.
- Table 2
- Figure 2
Our first winter 2007/2008 was the coldest, with temperatures dipping to minus 50°F. High tunnel air temperatures were consistently warmer than the exterior plots while soil temperatures remained warmer outside (Figures 7 and 8).
In the second winter, temperatures once again dropped to nearly minus 50°F in January (Figures 9 and 10). The high tunnel environment remained consistently warmer with 10 to 15 degrees (Figure 9). As in the previous season, we noticed more fluctuation and lower soil temperatures inside the tunnels compared with the exterior plots (Figure 11).
Temperatures for the winter of 2009/2010 showed similar trends as previous years, with high tunnel air temperatures staying consistently higher than outside (Figures 12 and 13). When comparing temperatures from various locations inside the high tunnel, we saw slightly higher temperatures from the center of the high tunnels as opposed to the ends or outside rows.
We measured PAR and SR inside and outside the high tunnels since 2007. The plastic covering material (seven oz polyethylene mesh) provided a shaded high tunnel environment (Figures 14 to 19). The reduced light intensity moderated high tunnel temperatures during summer heatwaves while supporting the growth of the trees. The mesh covering material was chosen to provide sufficient strength withstand the weight of snow during the winter months.
When comparing light and air temperature in early spring and summer, the high tunnels, while maintaining slightly lower PAR measurements, have considerably higher air temperatures than the exterior plots, which seems to make the difference in the onset of flowering, which occurs in early- to mid-May in the high tunnels, and late May, if at all, in the exterior plots. Additionally, only the trees in the high tunnels produced fruit (Figure 20 and 21).
In the summer months, the high tunnel covering material filter PAR to reduced values compared to uncovered field conditions, while maintaining temperatures between 55 and 85°F. Although PAR remained high in the exterior plots, the air temperature was lower than in the high tunnel environment (Figure 22 and 23).
Survival rates were generally consistent each year with the largest percentage of tree survival occurring in the high tunnels (60 % overall in tunnels versus 40% outside). We replaced tree mortalities after the first winter. No replacements were made after the second season. There were anywhere between one to eight trees for each variety. None of the other types of fruit trees (cherry, pear or plum) survived the first season. It should be noted that in 2008, when the replacement plants were tallied for survival, a higher survival percentage of these trees occurred outside compared to inside the high tunnel (Figure 24).
We had trees set fruit after our first season and experienced a steady increase in fruit set each consecutive year. In 2010, 77% of the trees inside the high tunnels set fruit. Six trees flowered outside, but only one produced fruit. Flowering occurred the second week of May for the high tunnels and almost the fourth week of May for the outside trees. Not all of the trees that flowered produced fruit (Tables 4 and 5).
The 2010 season was our highest yield thus far at 186 kilograms (410 lbs). The fruit yield varied widely among varieties from over 18 kg to as little as 0.14 kg (Table 6). A total of 28 varieties produced fruit in 2010.
We measured the soluble solid content in Brix (°Bx) as an estimate of the sugar content for each variety using a refractometer (Atago® digital hand-held PAL-1 refractometer from Spectrum Technologies, Plainfield, IL.). At least four apples were randomly selected of each variety and the averaged results are presented in Figure 25. The values of Brix varied among tested varieties from 3 to 13°Bx.
Taste tests were done on some varieties in order to assess characteristics and properties of the varying varieties (Table 7).
We tested some of the varieties by various methods including baking, drying and saucing fruits. Many dried well when prepared shortly after harvest. Several varieties (Chinese Golden Early, Parkland, Golden Uralian) were best consumed immediately after picking. Others (PF 12, 18-10-32, Advance and Prairie Sun) stored well in cold storage. We were not able to run tests on all varieties but made numerous observations that we intend to use in a publication on apple varieties.
The preparation of the site and construction of the high tunnels were major undertakings. Constructing two very large high tunnels required significant resource and manpower inputs. We would suggest smaller tunnels, or just one tunnel, for personal use or rural communities in interior Alaska. Testing the site initially with one tunnel might also be a good idea before installing more than one tunnel. The space required for a large high tunnel is not always available in remote communities, so the use of smaller high tunnels may be more convenient in these cases.
We would also suggest trying to find resources for building a high tunnel locally as shipping costs can be high for remote communities in the interior. The use of several smaller high tunnels or low tunnel row covers may work better in remote communities. Even finding partial resources may help to reduce costs and make the addition of a high tunnel more profitable. Some items to consider for smaller tunnels (e.g. 6 x 12, 6 x 14) are rebar and pvc pipe or wood and small metal piping. Larger tunnels (e.g. 20 x 40 and up) may require more ingenuity depending on what’s available.
Warmer air temperatures in the high tunnels throughout the winter clearly benefit the high tunnel trees by effectively blocking the wind and reducing stress to dormant trees. While soil temperatures tend to be warmer outside, particularly with significant snow cover, the colder soil temperatures in the high tunnels have not translated to reduced growth. Plants inside the high tunnels are much larger and healthier than trees outside. Leaf development and appearance usually lag behind with 10 to 14 days outside.
In the spring, the high tunnels were warmer with 10 to 15°F compared to the outside. The warmer spring temperatures resulted in earlier leaf and flower bud appearance. Fruit trees normally require at least five years to reach sufficient maturity to produce fruit. The modified environment of the high tunnels has been adventitious, resulting in fruit production of recently planted trees as early as after two growing seasons. Fruit production has consistently increased with each growing season. In contrast, only a very limited number of trees have flowered and produced fruit in the outside plantings.
Survival and Harvest Data
Several varieties were successful at our test site in Fairbanks (Table 3). Some that did particularly well in the high tunnels include Alice, Altaiski Sweet, Arctic Red, Carroll, Chinese Golden Early, Collet, Garland, Norland, Norson, Nova Sibirski, Parkland, PF-12, Prairie Magic, Prairie Sun, Ukalskoje and 21-61-69 (all over 60 percent survival). There were a few varieties that did better outside than inside ( e.g. Lee 17, Lee 21, Heyer 12) and a few that did the same regardless of inside or outside the high tunnel (e.g. Parkland, Norhey, Red Heart, 18-8-11). The relatively mild winter and decent snow cover the first year was a real benefit to the establishment of the trees. Survival overall tended to be higher in the high tunnels, with the exception of the replacement plants in 2009, which had a higher survival rate outside (Figure 24).
The high tunnels showed an advantage for tree establishment and growth compared to exposed sites. In addition, flowering and fruit development have primarily been recorded so far, in the high tunnels. Some trees have flowered outside in both 2009 and 2010 (Lee 21, Heyer 12, 8919, Norland, Red Heart, Altaiski Sweet) but only one tree has produced fruit so far (2010), Heyer 12.
Due to the many varieties tested, it is difficult to make comparisons among trees regarding yield and individual fruit quality. Variation in fruit production even among similar varieties was inconsistent in some cases (e.g. one tree with a few fruits vs. many trees with varying amounts of fruit). As the trees mature, we can monitor and measure variety success with more accuracy. Once the outside trees begin to produce fruit, we can make comparisons in yield and quality with the high tunnel trees.
High tunnels are beneficial to fruit tree establishment, fruiting and flowering in interior Alaska. We cannot determine whether productivity is greater within the high tunnels until the trees outside begin to produce and we have a product to compare. So far, the high tunnels have proven to be beneficial in promoting early flowering and fruiting and season extension.
The trial is still in its infancy given that most fruit tree trials run a minimum of ten years. We hope to continue monitoring the trees for at least another five years in order to determine which varieties are the best suited for interior Alaska.
- Soil (red) and air (blue) temperatures inside a high tunnel from December 2007 to May 2008.
- Figure 9. Soil (red) and air (blue) temperatures, high tunnel, Sept. 2008 – Sept. 2009.
- Figure 10. Soil (red) and air (blue) temperatures, exterior plots, Sept. 2008 – Sept. 2009.
- Figure 11. Minimum and maximum air and soil temperatures in high tunnel and outside (exterior) plots in 2008 and 2009.
- Figure 15. Photosynthetic active radiation (PAR, µmol· m-2s-1) from an exterior plot for the month of January, 2010.
- Figure 17. Photosynthetic active radiation (PAR, µmol· m-2s-1) in an exterior plot for the month of July, 2010.
- Photosynthetic active radiation (PAR, µmol·m-2s-1) in the exterior plot from April 25 to June 1, 2010.
- Figure 20. Photosynthetic active radiation (PAR, µmol·m-2s-1) and air temperature (°F, blue, right axis) in the high tunnel for the month of April, 2010.
- Photosynthetic active radiation (PAR, µmol·m-2s-1) and air temperature (°F, blue, right axis) in the exterior plot for the month of April, 2010.
- Photosynthetic active radiation (PAR, µmol·m-2s-1) and air temperature (°F, blue) in exterior plot l, for July, 2010.
- Formation of flowers (Flw) and fruit of trees in the west high tunnel. The information is arranged based on the location of the trees starting from the north.
- Brix value (°Bx).
- Soil (red) and air (blue) temperatures for the exterior plot during the 2009/2010 winter (December through April).
- Photosynthetic active radiation (PAR, µmol·m-2s-1) and air temperature (°F, blue), in the high tunnel, for July, 2010.
- Figure 12. Soil (red) and air (blue) temperatures for the high tunnel during the 2009/2010 winter (December through April).
- Survival percentages (alive/total planted) for replacement plants (2009), second season (2009), first season (2008) for high tunnels (blue) and exterior plots (red).
- Survival (percentage live trees) for all apple varieties 2007 – 2010 in the high tunnels, outside plots and combined.
- Yield of apples for each variety. The number of trees is indicated in parentheses.
- Apple taste test for selected varieties inculding Brix (°Bx) values.
- Figure 8. Soil (red) and air (blue) temperatures in exterior plots from December 2007 to May 2008.
- Photosynthetic active radiation (PAR, µmol· m-2s-1) in the high tunnel from April 25 through June 1, 2010.
- Formation of flowers (Flw) and fruit of trees in the east high tunnel. The information is arranged based on the location of the trees starting from the north.
- Figure 14. Photosynthetic active radiation (PAR, µmol· m-2s-1) within the high tunnel for the month of January, 2010.
- Figure 16. Photosynthetic active radiation (PAR, µmol· m-2s-1) inside the high tunnel for the month of July, 2010.
This project has generated much interest in Fairbanks as well as throughout the state. I have met with local fruit growers in Fairbanks to compare and discuss the success of the high tunnels and given numerous impromptu tours of our facilities. We are located in a highly visible area, and people will often stop by to have a look. Our goal is to generate enough interest locally to start a Fruit Growers Association in Fairbanks, which I hope to help coordinate. Depending on funding, we hope to be able to have such a group available this spring/summer. Many local growers have offered to showcase their orchards and to share their knowledge with anyone interested in fruit production. It is our hope that this project will inspire individuals and communities throughout the interior (and beyond) to experiment with apples and other fruits suitable for our environment. I cannot count how many people have approached me to say that they are very excited with the success of the trial and express genuine interest and support for continued success.
Our website has been a powerful tool in helping to disseminate our research (www.uaf.edu/ces/ah/fruit-tree-trials/). We have all of the annual reports available and will also have the final report posted as well.
Educational & Outreach Activities
We hope to produce two main publications from this research:
1. Apple Varieties Suitable to Interior Alaska
2. High Tunnels for Fruit Production in Interior Alaska.
We also hope to contribute to a more general high tunnel publication that will explain the technology of the high tunnels and outline the range of possibilities in high tunnel use for the interior.
These publications are to be produced no later than August of 2011.
As mentioned previously, we also hope to provide local growers support in forming a Fruit Grower’s Association, which will depend on funding availability and public interest.
Areas needing additional study
We have only completed three full growing seasons of this trial. In order to compare productivity and fruit quality between exterior and high tunnel trees we must continue to monitor the trial. We hope to obtain funding that will allow us to proceed with the trial for at least another six years. There is much that remains to be discovered regarding the effectiveness of the high tunnels in fruit production in interior Alaska.