Globe artichokes have been traditionally grown in northern areas as an annual crop due to the cold winter temperatures experienced in this region of the country. Our project investigated the ability of globe artichokes to be grown as a perennial crop using low tunnels for winter protection. We were able to achieve an average survival rate of 48% from the total planted in the first year. We had a high variability of survival between the plots from 76% to 20%, this can be attributed to the location of the plots on the farm, the highest survival rate was in the plot with the most well drained soil. We planted seven different varieties, equally represented between plots, and found large differences in yield and germination rate between each variety. The comparison of yield between crops is also highly variable, and this might also be attributed to location of the plot.
Globe Artichokes are a desirable vegetable grown primarily in California then shipped to New England markets and beyond. One of the main reasons that there is a lack of locally grown globe artichokes is due to the cold winters in New England causing the ground to freeze to depths of 4 feet. When the ground freezes that deeply, it damages the taproot of the plants, generally globe artichokes grow in zone 7, our farm has a cold hariness zone of 5. We wanted to determine if using some extra insulation would allow the plants enough protection to make it through the winter. Low tunnels are used to extend the season for many other crops that grow well in cool weather, it could possibly work for globe artichoke because they are a cool season crop. We also wanted to know if the artichokes would produce more each successive year after the first year even if some plants did not winter over. We thought this would prove true because globe artichokes get the biggest bloom from the center of a shoot, and each plant produces more shoots each year. We tested a system of overwintering globe artichokes by using low tunnels covered with a heavy duty woven fabric and mulched with a chopped straw mulch.
The objective of this project was to evaluate overwintering perennial globe artichokes using low tunnels, and compare that to growing globe artichokes as annuals. We evaluated the ability to harvest globe artichokes sooner from perennial plants, as well as the higher quality harvest from perennial plants, because the perennials plants produce a more uniform harvest from year to year. We looked at the potential cost saving of perennial plants versus annual plants, as well as the potential profit from the longer season that perennial globe artichokes have. All the globe artichoke plants were grown using IPM and organic weed management following a sustainable approach to crop production and this project would need to grow successfully under these management practices to be successful for our purposes. We wanted a growing system that we could show to customers purchasing globe artichoke seedlings, and could easily be adapted to their own site. We wanted to be able to in increase sales of seedlings, as well as let them know we would have globe artichokes for sale later in the season from the farm stand.
Our main measure of success was for >40% survival rate and to lengthen the harvest window for fresh market sales.
We started seven varieties of globe artichoke seed on March 24, 2014 in plug trays filled with a mix of ProMix BX and worm castings and placed on a heat tape in the greenhouse. The plants were given a plant starter food by Epsoma. The seedlings were transplanted to 4″ perennial pots on May 6, 2014. The soilless medium used was Vermont Compost Fort Vee and Fafard 38 mixed together in a 50/50 ration. One tablespoon of Epsoma Biotone was mixed into each pot. The plants were moved to a bench in an unheated high tunnel two days later.
The plants were transfered to an outside bench sheltered from the wind on May 12 to chill them and vernalize the plants to produce buds the first year. The plants needed to be exposed to approx. 2 weeks of temperatures below 50 F to induce flowering in the first year. Plants were transplanted into prepared plots on May 28, 2014. The holes were 12 inches deep, one pint of peat moss was added to each hole. In addition, each hole received a 1/4 cup measure of ProGro organic granular fertilizer and incorporated. The plants were spaced three feet apart in three staggered rows in plots measuring 6′ x 24′, this allowed for 26 plants per bed. The varieties of globe artichokes we trialed were Imperial Star, Green Globe, Emerald, Violetto, Opera, Carciofo Romenesco and Violetto Di Chioggia. Pest management was done using Spinosad to control Aphids.
We examined the hardiness, germination rate, yield and vigor of the plant. The last harvest was on November 2, 2014 and once the ground began to freeze and cold temperatures were steady the plants were trimmed back to 2 inches from the ground, covered with 12-18″ mound of chopped straw mulch and a low tunnel to encase the planting plot. The low tunnels were made by bending 3/4 inch metal tubing using a pipe bender made specifically for this purpose. The low tunnels were covered on December 10, 2014 with Agribon+ AG-70 and weighed down with long 2×6 boards along the length of the sides. We took soil moisture and soil temperature readings as well as air temperature readings inside the low tunnels throughout the winter. One rodent trap was placed in each low tunnel to help reduce the population of rodents, we used multi-catch traps.
Two of the data loggers malfunctioned, leaving us with incomplete data for analysis. We opted to treat each plot the same and not leave one plot uncovered as the forecast for temperature to drop drastically meant that the plants would not be prepared for such a sudden freeze.
The low tunnel was removed on April 18, 2015, we did not pull back the mulch fully from the plants, we wanted to allow the emerging plants some time to adjust. Some of the plants were emerging and pushing the mulch up, these plants we removed the mulch and made a high ring of mulch around the plants to create a small amount of protection from wind damage. The plants were fertilized monthly during each growing season and weeded as needed.
We used IPM to manage pests and there was limited need to spray Spinosad to control aphids. Lady bugs took care of a majority of any aphid problems.
In the first year, the edible buds that were harvested starting August 8, 2014. We continued to harvest steady until September 30 when we tallied the total harvest. There were additional buds harvested until November 2, 2014, many of these were small and not of a marketable size.
The total harvest up to September 30 was 58.54 pounds and the total number of buds was 325. There were two varieties that performed well in the first year; Imperial Star yielded 29.29 pounds and Opera produced 24.90 pounds. Imperial Star and Opera combined made up 92% of the total harvest for the season. The Opera variety produced unique purple colored buds, and these in combination with the green of the Imperial Star would be a stunning display at a farmers market. We were able to compare the annual yield by variety (figure 1) and there is a variability between the variety, and one heirloom variety that did not produce the first year. This variety did produce the second year and would not be recommended since the spines were very sharp and would gop through gloves. This variety is the Carfiofo Violetto Di Chioggia, and comes from Italy from Bavicchi seed company.
The survival rate of the overwintered globe artichokes was between 76% and 20%, depending on the location of the plot. We were not able to get per variety survival rate due to plant markers getting moved during the winter preparation. There was equal representation of all varieties between the plots the following year, leading us to believe that the survival rate difference is more due to the location of the plot rather than the varieties. However, we had limited purple buds the second year, and this unique color would only appear on Opera and Violetto. Further study is needed to determine for certain however it may be the Opera is not a good choice for a perennial planting system. The plot with the highest survival rate was the plot located in the most well drained area of the farm. The survival rate between plots also factored into the comparison of total yield from each plot year to year (figure 2).
The germination rate for the seven different varieties had a high degree of variability (figure 3). Imperial Star had the highest germination rate of 87% and the lowest rate was 10% from the heirloom variety Carciofo Violetto Di Chioggia. Going forward we will plant Imperial Star, Opera, Green Globe and Romanesco in our gardens. These varieties had the best all around performance and the color and shape variety that they offer help attract buyers. Next year we will replace empty spots left from plants that did not survive the winter with an annual planting. This will extend the season of harvest from July until October with very little gaps.
Our survival rate, by plot, was between 20% – 76% for the globe artichoke plants. The plants were much larger the second year and had multiple main shoots, producing multiple buds per plant. There was a difference in the harvest dates from annual production as compared to perennial production. The date of first harvest in 2014 was August 8 and continued to the last harvest date of November 2. (The last harvest date was not included in our yield data set) The first harvest date in 2015, after the plants wintered over, was July 4 and continued until August 10, then the plants slowed due to the high heat of summer. The plants grew new shoots and the harvest began again on October 3. As of this writing the plants were still producing a few buds per plot, remained green, and holding up to a few hard frosts.
Education & Outreach Activities and Participation Summary
A brief write-up has been submitted to the Fruit and Vegetable Newsletter put out by Dr. Becky Sideman from UNH Cooperative Extension. The newsletter will be release this November. Please see copy of newsletter below.
We will be presenting our research and the technique of how to overwinter globe artichokes at the NOFA-MASS winter conference on January 16th, 2016.
We belive that this growing system for globe artichokes has the potential to be scaled up to a rollable high tunnel model in conjunction with tomatoes. The globe artichokes do not need to be covered until late in the fall, after the tomatoes would be cleaned from the high tunnel and the globe artichoke plants are stumped allowing for ease of moving the tunnel over the globe artichokes for winter protection. There is a possibility to then intercrop some cold season crops to grow in the unheated tunnel in between the dormant globe artichoke plants. In the spring the rolling tunnel can be moved off from the globe artichoke plants and into position to warm the soil for the tomato planting.
Another recommendation would be incoporating annual and perennial planting on the same farm to keep a steady harvest from July-November. The annual globe artichoke plants fill in the gap when the perennial plants slow due to the heat.