Artichokes (Cynara scolymus) are a cool-season vegetable that may have application for diversification of cropping in cold climates. Artichokes are a frost-tolerant but freeze-sensitive perennial often grown in cold climates as an annual. Over two years, we evaluated commercially available artichoke cultivars for over-wintering potential and tried a variety of plant protection techniques to mitigate cold winter temperatures that kill all artichoke buds. Our studies showed that extreme cold temperatures resulting in the ground freezing caused nearly complete winter-kill of all varieties tested. Violetto appeared to be more cold tolerant than other cultivars evaluated. Soil and plastic mulches did not improve artichoke survival. Snow cover and straw and leaf mulches did improve artichoke surviva1. We can recommend Violetto as a possible genetic source for cold tolerance, but it has poor commercial qualities. We can recommend straw and leaf mulches for further evaluation for artichoke over-wintering in the field as an approach to growing this crop in the Intermountain West.
1) To evaluate commercially available artichoke cultivars for over-wintering in Intermountain west.
2) To examine in field over-wintering techniques for artichokes.
3) To distribute this information to urban and rural farmers and home gardeners of the Intermountain West at local field days, at extension educational events, and through print and electronic forms.
METHODS OR APPROACH
OBJECTIVE 1: EVALUATION OF COMMERCIAL ARTICHOKE CULTIVARS
Artichoke seeds from a variety of commercial sources were surface sterilized (10% hypochlorite), rinsed four times, wrapped in moist paper towels, then placed in plastic bags and stratified in a 40F refrigerator for one week starting on January 17, 2006. The seeds were then removed from refrigeration, left in the plastic bag in the moist paper towels and placed in a warm site (60-70F) for several days until germination occurred. A previous test trial with 25 seeds of Dayton F2 hybrids, an artichoke-cardoon cross, had obtained 88% germination with this stratification procedure.
The germinating seeds were then planted in 4-inch pots containing a soil seedling mix. Seedlings began emerging in about one week. We planted 1022 pots, cared for them in an IPPFBE, Inc. greenhouse until February 16, and then moved them to the Utah State University research greenhouse to grow out.
Artichokes varieties (PI Globe, Green Globe (N), Violetto, Emerald, North Star, Imperial Star, Purple Romagna, Green Globe (Be), and locally generated Dayton F2 hybrids) were included in the initial trial. Seedlings were grown for 3 months before being transplanted around northern Utah. Planting sites included the Utah State University Kaysville Research Farm, an IPPFBE, Inc. site in Richmond, UT; James Haggarty’s Sun River Farm in Tremonton, UT and in southeastern Idaho on the Jeff Hobbs’ Franklin farm. Plants (18-27 plants of each variety at each location) were transplanted. The IPPFBE, Inc. site was planted March 2, 2006, to evaluate tolerance to early spring frosts. The other sites were planted between May 10 and June 6, 2006. Plants were spaced 2.5 feet apart in-row with rows spaced 5-foot apart. All plants were planted in bare soil except at the Kaysville site where plants were planted through black plastic mulch (for weed management) with drip irrigation. Plants were irrigated as needed, weeded periodically and growth assessed in October. Growth measurements collected at Kaysville included plant stands, leaf biomass, and suckering (assessment of new growth) where next year’s newer stalks will originate.
OBJECTIVE 2: OVER-WINTERING TECHNIQUES
Over-wintering Techniques–Fall 2006. Various cover treatments were assessed to determine the potential to over-winter artichoke roots in the field in northern Utah and SE Idaho. Not all treatments were used at all locations as each cooperator was interested in assessing materials readily available on their farms.
Kaysville Research Site–2006: Three mulching treatments were tested for artichoke survival. First, after mowing the leaves off of all the artichoke plants, we removed the plastic mulch and hilled up 6-8 inches of soil over top of the row. This was the control treatment. Second, we applied clear plastic mulch over the mounded soil. Third, 8-10 inches of wheat straw was applied over top of the mounded soil. KoolTrak (www.kooltrak.com) temperature sensors were placed 2 inches deep in the soil directly over an artichoke crown. Temperatures were record hourly within each mulch treatment from early December 2006 to late April 2007. In April, artichoke shoot emergence for the different cultivars was assessed as the number of shoots to emerge per plot.
Farmer Tested Over-Wintering Treatments–2006 & 2007. In November, field soil (4-6 inches) was mounded over all of the plants at the SunRiver farm in Tremonton UT and then one-third of the site was covered with commercial white plastic mulch, one-third was covered with straw, and the rest just had soil over the crown. At the Richmond site of IPPFBE, Inc., plants were cut back to ground level and were mulched with 4-6 inches of sawdust, leaves, or cut artichoke leaves the soil to 12 inches. Field soil (6-8 inches) was mounded over half the plants at the Hobbs farm in Franklin ID and then these were covered with commercial white plastic mulch. The other half was covered with 12 inches of composted manure.
RESULTS AND OBSERVATIONS
Objective 1: Variety Evaluations -Richmond, UT: Tolerance to early spring freezes following transplanting appeared to vary in five varieties tested at the IPPFBE, Inc. site spring 2006. Although the artichoke is frost tolerant and requires chilling temperatures to flower, freeze damage resulting from transplanting to early May significantly affects plant survival and production.
Artichoke survival early spring planting IPPFBE, Inc. 2006 was as follows: Purple Italian Globe, 18 planted March 2, 2006, 11 survived to May 11, 2006, or 61%; FW (local cross), 36 planted March 2, 2006, 28 survived to May 11, 2006, or 78%; Purple Romagna, 18 planted March 2, 2006, 8 survived to May 11, 2006, or 44%; North Star, 18 planted March 2, 2006, 11 survived to May 11, 2006, or 61%; 18 planted March 2, 2006, 16 survived to May 11, 2006, or 89%;
Objective 1: Variety Evaluations -Kaysville, UT: There were obvious differences in plant growth and flowering potential (suckers and flowers initiated during the first year–November 21, 2006) between the nine commercial varieties tested).
Violetto grew very large plants and had approximately 3 suckers per plant, but the flowers produced in the first year were very small and spiny and of inferior quality. Emerald, North Star, and Imperial Star had limited vegetative growth but produced adequate numbers of suckers, and some flowered well in the first year with good size buds produced. The open-pollinated Dayton F2 hybrid grew well, produced a lot of suckers and flowered well but had plant and flower characteristics similar to the cardoon parent. The Green and Purple Globe varieties were generally small in size, suckered adequately but had poor flowering characteristics in the first year.
On June 6, 2006, artichokes were planted at Jeff Hobbs’ farm in Franklin Idaho using a transplanting implement. Plant size made it difficult to get the plants set properly and many had to be hand set. From field preparation to final plants in the ground took about 2 hours (3 sets of each variety, 244 plants). Bryan Dayton visited Jeff’s field planting 3 times in July. Weeds tended to be a large problem with many weeds competing with the plants. Weeds cultivated and Treflan herbicide was applied. By the last of July weeds were again competing though the plants were large enough to withstand competition.
On November 8, 2006, plants grown on the Hobbs’ farm were evaluated a second time. The grower reported that there was a lot of variation in performance and some had flowered in the first year. There was a great deal of weed competition during the season and the early season application of Treflan (pre-emergent herbicide) was probably responsible for the growth differences. Weed control was poor and some other method of weed management was needed if the crop was to be grown successfully. Jeff Hobbs also noted that late in the season there was a lot of rodent damage with animals feeding down in the crown of the plants. The leaves remaining on the plants in the field were cut off on November 18, and the following treatments used to cover the plants for overwintering. The first row and a half was covered with 6 inches of soil and then had white plastic mulch over the soil. The remaining half row and the next full row were covered with 6 inches of soil. The last two rows were covered with 6 inches of composted manure. The composted manure was applied with a manure spreader then raked over the row to mound it up (~ 6 inches). Several problems were noted when applying the treatments. First, after mounding soil over the plants, the plastic mulch layer scraped holes in the top of some of the plastic where the hills were steep and high. Jeff recommends going along and knocking them down a little. Some of the artichoke rows were 4 feet between rows and some were 5 feet between. The narrow rows were too close together and the tractor ended up running over the rows. Jeff said it made it difficult to put down the plastic over the narrow rows so he thinks 6-foot row centers would work well.
James Haggerty, SunRiver Farm, planted his artichokes on June 8, 2006. James planted 24 plants of each variety. On our return visit on July 19 the plants looked good and were growing vigorously. The artichokes were beginning to flower and his neighbors loved them. James had lots of problems with weed control since he is restricted from using herbicides on his organic farm. We visited the farm periodically to evaluate the plants. Around November 20, James called to say he was ready to cover his planting area with soil. Bryan met him at his Tremonton farm and together they evaluated the varieties and showed him how to cut them back. The majority of the plants that flowered had several large suckers at their base though no specific data were collected on this growth aspect. The vegetative plants (those that did not flower) did not have suckers. Those plants that produced flowers tended to be smaller – all their energy went to seed production. A large variation in plant size and vigor was noted. The mulching treatments applied included soil over all the plants, then white plastic mulch over one-third and straw over the other third.
Variety Evaluations: Over-Winter Survival-Kaysville: Of the 207 artichokes planted in the spring of 2006, only 9 (4.3%) of the plants survived the winter (2006-07) and resumed growth in the spring of 2007 (data collected April 15). All of those to survive were from the cultivar Violetto (9 of 25 (36%). In several of the farmer trials, Violetto also had some survival percentages (20-30%) when mulched with soil, straw, compost or manure. However, the low numbers surviving, low vigor of re-growth and the poor horticultural quality of Violetto makes this a poor choice for production.
Over-Winter Survival-Participant and Farmer Comments: Bryan Dayton noted that he began uncovering plants at the IPPFBE, Inc. site on March 17, 2007. From his measurements, the crowns were covered to 5-7 inches deep with mulch. The only artichokes that appeared alive were those mulched with leaves, as there were some shoots beginning to grow. The artichokes under other mulch treatments (soil, sawdust, and plastic mulch combinations) had no growth, the buds were mushy and root tissue looked like there was freeze damaged down several inches into root. James Haggerty and Jeff Hobbs reported on April 15, 2007, that every artichoke on their farms seemed to be dead as they could not see any new growth. It appeared that most of the mulch treatments trialed do not sufficiently protect the crown from freezing.
Winter Temperatures -Kaysville: The winter of 2006-2007 was generally cold with little snow from mid-November to mid-January. Open winters without snow cover allow soil temperatures to drop well below freezing and this would significantly impact survival of artichoke roots and suckers. Soil temperatures at crown depth (2-3 inches) during December, January, February, and March were recorded and summarized. Cold soil temperatures during December, January, and February caused the soil to freeze down to crown level and is likely responsible for significant crown damage and plant losses. Intermittent soil warming in February and March 2007 followed by periods of cold may also contribute to a reduction in plant survival. Warming would allow resumption in growth and if colder periods follow that, crown dormancy is lost and new growth may be damaged by the colder temperatures. Our attempts to cover the crown and protect them from cold was not completely successful, although those artichoke crowns mulched with straw did have more stable temperatures with fewer periods when temperature dropped below freezing throughout the winter months. This may explain why Violetto had some survival and re-growth in the spring of 2007.
YEAR 2–Artichoke Assessment
Stratification was done on December 21, 2006, using the remaining artichoke seed from those purchased the prior spring (approximately 300 remained). After these germinated and were planted (see earlier protocol), plants were raised by Dan Drost at the USU Research Greenhouses. On April 24, 2007, the artichoke plants were transplanted at the IPPFBE, Inc. site. Some of the plants were sent to James Haggerty for planting (May 4) and retesting, and the remainder was planted at Jeff Hobbs’ farm on May 9. Jeff planted his through black plastic to help with weed control.
In the fall, November 3, 2007, Bryan Dayton collected fallen tree leaves and mulched all artichokes at the IPPFBE, Inc. test site. On one mulch trial, the leaves were kicked up around the plants but the artichoke leaves were not cut. On other trial the artichoke leaves were cut off, mulched with tree leaves then covered with the artichoke leaves to keep the dry tree leaves from blowing away. Jeff Hobbs mulched his artichokes with straw on November 26. It snowed 1 foot the next day. On January 15, 2008, Bryan measured soil temperatures at the IPPFBE, Inc. site with a hand probe thermometer. The snow was 6 inches deep over the mulch and the soil was not frozen even in areas of no mulch. Bryan noted that there was quite a bit of deer damage with those mulched with tree leaves but where the artichoke leaves were not cut off. Those artichokes cut to the ground before mulch seemed to be less disturbed by deer. Garden soil with no mulch: 35degrees F; Artichoke (uncut) with leaf mulch: 37degrees; Artichoke cut to ground with leaf mulch: 38 degrees; Artichoke (uncut) with leaf mulch disturbed by deer: 36 degrees.
Bryan Dayton evaluated his mulching treatments in the spring (May 29, 2008). Almost 100% of artichokes survived the winter. There had been more than 1 foot of snow on artichokes throughout the winter. There was no difference in survival between those artichokes that had their leaves cut off before applying leaf mulch or those plants where the leaves were not cut off and then leaf mulched. The snow appears to moderate the ground temperature. All surviving artichoke plants grew vigorously in the spring.
A series of field days have been conducted to address objective 3.
a) Artichoke plants were planted at the Cache Valley community garden and at the Salt Lake community gardens for community education. This was coordinated through Utah State University Cache Valley Extension and TreeUtah. Inc.
b) 22 horticulture students taking the 2006 Vegetable Physiology and Production course offered by Utah State University toured the artichoke variety trial on Thursday October 26, 2006. Students were introduced to the artichoke project, observed the various varieties, assessed their flowering habit and discussed the different over-wintering strategies with Dan Drost. Student input on potential outcomes was explored.
c) Franklin County Agricultural and Noxious Weed Tour took place on July 11, 2007. Artichoke plants, the different varieties grown, suspected hardiness, and potential over-wintering techniques and commercial opportunities were discussed. About 35 farmers and Agriculture Professionals from southern Idaho participated in the tour and viewed the artichoke planting at Jeff Hobbs’ farm.
d) It was our intention to feature the findings of the Kaysville project at the July 2007 summer horticulture field. However, due to death of nearly all the plants in the trial, we cancelled that segment of the program for a lack of materials to show to the participants.
BENEFITS OR IMPACTS ON AGRICULTURE
While annual artichoke production approaches have been tried and proved successful, they are deemed expensive (annual seed, plant production, planting, maintenance and harvest costs) and only modestly productive (flower bud yield). Identifying an over-wintering method for artichokes could help reduce annual establishment costs and could result in higher levels of production. Being able to reliably grow perennial artichokes rather than annual artichoke would allow growers to diversify their production and be able to provide a new product to local markets during a period of the year when there is a short supply of artichokes.
The cooperating growers (Jeff Hobbs and James Haggerty) were interested in devising ways to integrate a new crop into their farm operations. Jeff Hobbs had never grown artichoke before and thus it was a new learning experience. James Haggerty had grown some artichokes as annual plants but had never tried over-wintering the plants. The participants realized that this study did not identify an artichoke cultivar that had both high horticultural qualities and cold tolerance; nor was a consistent over-wintering method identified to grow artichokes in Northern Utah and Southeastern Idaho. Neither grower is currently pursuing this venture further. Dan Drost was contacted by a grower from near Reno, Nevada, about over-wintering artichoke. Their discussion centered on the techniques used in Utah and how cold it got in the winter in western Nevada. After that discussion, the grower decided that this may not be the best way to grow artichokes in his area.
While the project was quite interesting and growing a new crop was challenging, without a successful over-wintering method or more cold-tolerant plants to increase artichoke survival, the establishment costs, plant maintenance costs, and plant covering expenses would not be recouped, and therefore the systems is not viable or sustainable.
At present we cannot recommend commercially growing artichokes as perennials. While annual production practices are successful, to date all attempts to over-winter artichokes in the colder areas of northern Utah and southeastern Idaho have met with limited success. A home gardener may have some success overwintering artichokes using heavy mulch with leaves or straw, especially in years with heavy snowfall. Commercial perennial artichoke production in the Intermountain west may be accomplished in the future through improved mulching systems and selection of a cold tolerant, commercial quality artichoke.
While there was only limited outreach due to nearly a complete loss of the 2006 planting, what we have learned is going to be included in our Utah vegetable grower’s newsletter in January of 2009.
IMPACTIONS AND CONTRIBUTIONS/OUTCOMES
1) Commercial artichoke varieties germinate and grow well and produce flowers in the first year of growth under Utah and Idaho growing conditions. 2) Productivity as measured by plant biomass (size), flower number, and sucker production varied greatly between the different varieties grown. Violetto produced very large plants, suckered modestly, and produced some flowers in the first year’s growth. One limitation to Violetto was that the plants produced lots of spines and flower size was quite small. Emerald and Imperial Star, while not producing as large of plants, produced adequate numbers of flowers in the first year of good quality. Most of the other varieties evaluated grew poorly and did not flower well in the first summer. 3) Over-wintering artichokes involves growing plants of adequate size, removing the leaves at an appropriate time in the fall, and then mulching the plants so they do not freeze during the winter. We tried mulching with straw, compost, manure, soil, and clear or white plastic mulch. None of the different mulching techniques allowed adequate survival of plants through the winter. In one trial, 9 plants out of 218 planted (4.3%) survived the winter. None of the plants grown on Jeff Hobbs’ farm survived the winter in either year of the study. Bryan Dayton had poor survival the first year when there was less snow cover to add additional insulation to the different mulch treatments. In the second year of evaluation at Bryan’s test site, he had 100% survival but he also had a deep layer of snow to add cover to the mulches tried. Survival on James Haggerty’s property was very low. 4) At present, we cannot recommend to growers any of the overwintering techniques employed. 5) If growers are interested in annual artichokes we recommend purchase of either Emerald or Imperial Star. Chill the seeds for one week at 40F starting in late December or early January. Plant chilled seed in 3 inch pots and grow and care for seedling plants until early April. Transplant outside in April to ensure they get adequate chilling to initiate flower buds. Care for plants, weed regularly, water weekly, and most plants will start to flower in mid-to late-July. Plants generally bloom over a 2-3 month period. Harvest immature flower buds when they reach full size but before the bracts (bud leaves) begin to open. Cut off the flower bud with 2-3 inches of stem.