The purpose of this project was to evaluate growth and productivity of herbaceous peonies growing with and without late season high tunnels. The peonies were grown on cold permafrost soils on a north-facing slope. We anticipated that high tunnels would warm soil and air temperatures, promote soil drying and provide an environment that would maximize plant growth and productivity on marginal sites. By extending the growing season, we expected there to be more carbohydrate storage in the roots and a more vigorous plant the following year. Although the data does not indicate there is any significant difference between those plants in high tunnels and those outside, we still feel there may be some benefits to using high tunnels to grow peonies. The buds might be better without rain on them, especially white colored ones. Wet soils might stay drier without rainfall. More mature peony plants might show some of the results we expected in this experiment.
Recent research in Alaska has shown that peonies for cut–flower production is a viable northern agricultural product. Some of the limiting factors on Polar Peonies’ farm are the varied spring thaw, unpredictable early fall frosts and cold soils. This project used high tunnels in a field production setting to gather information on extending both the spring and fall seasons, as well as warming the soils. Potentially, this technology could allow production of peonies on cold soils or in micro–climate areas that are marginally too cold for successful peony production. This project addressed several of the limiting factors with the use of high tunnels in the following manner:
• increase spring soil temperatures for earlier and uniform plant emergence
• extend fall growing season (delaying frost) to increase the time for plant root nutrient storage, which will increased plant vigor
• increase overall growing season length to potentially allow production on colder, more northern sites, thereby providing alternative agricultural crop choices in other parts of the state which may now have marginal agriculture production.
While Alaska has had few sustainable agricultural exports, the current research, marketing and development of the peony industry indicates that this agricultural commodity is sustainable. Peonies are not available anywhere in the world during the Alaska harvest window during the months of July through September. Current demand far exceeds Alaska production and, therefore, there is substantial room of expansion of this industry in Alaska. With year-round peony cut flower availability now a reality, this has had an impact on the peony markets beyond Alaska – creating a steady demand for this commodity on the local, state, national and even international markets.
Identify the value of using high tunnels in field-grown peony production. To meet this objective we:
1. Monitored soil and air temperatures both inside and outside of high tunnels to determine impacts and optimum uses of high tunnel technology.
2. Determined spring emergence dates for plants inside and outside the high tunnels to determine if plant emergence timing was affected. Emergence dates were recorded for plants in plot areas. This was done over two growing seasons.
3. Determined if increasing growing days was possible with the use of high tunnels, especially extending into the fall. Data collection included visual inspection for frost damaged vegetation and data loggers to record air temperature on an hourly basis over the growing season.
4. Determined if there was increased plant survival and vigor with the use of the high tunnels. Data collection consisted of taking photographs and counting the number of stems in the plot area before harvest over three growing seasons.
5. Determined if there was increased flower production with the use of high tunnels. Marketable flowers were counted in plot areas over three seasons.
6. Monitor diseases by sampling and doing surveys in plot areas.
The high tunnel experiment consisted of six plots with three replicates under high tunnels and three replicates in the open field. Tunnels were erected in an existing peony fields during summer 2010. ‘Sarah Bernhardt’ peony plants were moved into plot areas to even out the number of plants in each plot area. Plots had two raised beds with double rows on each bed. Plants were 18 inches apart and there were 18 inches between rows. Each plot consisted of two raised beds that were 28 feet long and separated by a two foot wide alley. Fertilizer was broadcast in the spring at the recommended rate based on soil tests and again after harvest in mid-season. Plots were hand-weeded as needed, and Roundup was applied around plot areas for further weed control. Data on soil and air temperature, soil moisture, relative humidity, PAR and rainfall was collected using Hobo weather station (Onset Computer) recorded hourly throughout the year. Data on plant growth consisted of non-destructive analysis: flowering phenology, number of cut stems per plant and stem length. Spring emergence dates were recorded for plants inside and outside the high tunnels. Emergence dates were recorded for plants in plot areas over two growing seasons. Growing degree days were calculated to determine if increased growing degree days were possible with the use of high tunnels especially extending into the fall. Data collection included visual inspection for frost damaged vegetation and data loggers to record air temperature on an hourly basis over the growing season. Biomass samples were collected from five plants per plot at the time high tunnel covers were rolled up for the winter. Data collection consisted of taking photographs and counting the number of stems in the plot area before harvesting the plants and drying them. They were then weighed to determine if the plants inside the high tunnels increased in size faster than those outside. This was done over three growing seasons. Harvestable buds on the five biomass sample plants were to be counted to determine if there was increased flower production with the use of high tunnels over three seasons. Observations were made on disease and insect pests inside and outside of high tunnels on a regular basis throughout the growing season.
Description of Replicate sites.
High Tunnel Location Rep 1 no This rep. is closest to the woods and gets some shade.
Rep 2 Yes This rep is in the same row as rep. 1, down hill and not as well drained, also gets shade.
Rep 3 no This rep. is at the top of the field next to rep. 1, gets some shade.
Rep 4 Yes This rep. is at the top of the field next to rep. 3, gets some shade.
Rep 5 no This rep. is at the top of the field next to rep. 4, gets some shade
Rep 6 Yes This rep. is at the bottom of the field in the same row as rep. 5, it is very wet, no shade.
Growing degree days were increased inside the high tunnel but not by much. Summer 2013 was much warmer than 2012, so even though data collection was stopped earlier in the fall, the growing degree days were already more. It is interesting that early in the season there is more accumulation of growing degree days inside the high tunnels and then later, growing degrees accumulate faster in the non-high tunnels areas, at least in 2013. Also, Rep. 6 always accumulated more growing degree days, even though the plants in that rep. look the worst in appearance and size. It never gets shade.
The trend continues in the soil data. The temperature increases more rapidly in the high tunnels and later the soil outside the high tunnels catches up and even passes the high tunnel levels. We really do not understand why, but this might explain why as the plants mature, they all seem to be ready for harvest at the same time. We expected the ones in the high tunnels to be ready earlier, but that was not the case.
Plant emergence data was collected in 2012 and 2013. We expected the emergence dates to be more uniform in the high tunnels, and that was somewhat true in 2012. However, in 2013 it made no difference. The stems emerged over several weeks just the same as those not in high tunnels. They did emerge earlier inside the high tunnels in 2013, but it didn’t seem to make any difference in 2012. This would suggest the weather plays a much bigger role than the high tunnels. Spring 2013 was very late to warm up, and once it did, the temperatures were in the 70s or 80s and never cooled down again. It was about two weeks behind spring 2012. The plant growth tables show this trend. Biomass was collected on the same five plants in each replication for four years. While there was never any significant differences, early in the season and late in the season the plants inside the high tunnels looked a darker green and seemed to be growing more vigorously. As the growing season progressed, the plants outside the high tunnels caught up to those inside in size and appearance until the first frost, at which time they turned brown while those inside still looked healthy. We think the plants inside the high tunnels may have been water stressed, as the growing season progressed and they did not receive any rain. They were irrigated but because of the soil moisture levels, which we will discuss later, the levels of irrigation may not have been adequate for continued optimum plant growth.
We are not sure what soil moisture levels are required for optimum peony growth. However, peonies do not like wet soils. Other farms also were monitoring the soil moisture levels, and Polar Peonies fields were the wettest in the study. The data clearly shows the results of the cold spring of 2013. It took much longer for the field to thaw and drain down to a reasonable level. In 2012, when thaw occurred, the field drained quickly. High tunnel plots were irrigated twice during the growing season, once in the spring after fertilization to wash in the nutrients and once late in the growing season. It did not appear that any plot areas needed to be irrigated more than that. The soil was always moist, but the most logical explanation for the poor performance of plants inside the high tunnels is water stress.
There did not appear to be any increase in disease problems inside the high tunnels. We do have Botrytis spp. fungus infections in our peony field, but it is related to moisture and weed control more than being inside the high tunnel. In fact, since plants are kept dryer inside the high tunnel, it appeared they suffered less from this infection. We have not needed to spray for fungus control yet, but we do expect to during wet growing seasons.
Educational & Outreach Activities
We hosted farm work/sharing days in the fall of 2011 and 2012. Besides sharing how we use our high tunnels, we spread mulch, rolled up the high tunnel plastic coverings and shared with our visitors the challenges of growing peony in areas with cold, poorly drained soils.
In January 2014, at the Alaska Peony Growers Association (APGA) winter meetings, we will give a presentation on the final data collected during this project. There are usually more than 100 growers from around Alaska and a few from the Lower 48 states in attendance at the APGA winter meetings. In addition, peony growers and others interested will be able to access this report on line through several venues including the SARE website, APGA website and through Polar Peonies, LLC.
Peonies are a long living perennial crop, which does not appear to reach maturity until at least its fifth year in the ground, therefore we may not see significant changes as a direct result of the high tunnels until maturity, since there a large number of variables impacting the early growth years. We were able to share how high tunnels were constructed, different options for construction and how they might be utilized in other growing locations.
With global climate change arriving in Alaska, just like everywhere else, there may be a shift in agricultural production in our state. While more research needs to be done with high tunnels for peonies, there is also potential use of high tunnels for extending growing seasons in rural areas for growing currently marginal produce crops for greater self-sufficiency.
Our conclusion is: Do not grow them under these conditions if you have any other choice and think twice before investing lots of money and effort if these conditions are your only choice. Perhaps another crop would suit the conditions better.
Continued and future data collection on more mature fields of peonies may result in more significant differences between treatments that may assist the growing peony industry. High tunnels can help stabilize some weather – prevent excessive rain/hail for example – that can also be beneficial to more crops than just peonies.