Grafted Watermelon Production in Southcentral Alaska

Final report for FW17-026

Project Type: Farmer/Rancher
Funds awarded in 2017: $19,999.00
Projected End Date: 10/31/2019
Grant Recipient: Robert Brown
Region: Western
State: Alaska
Principal Investigator:
Robert Brown
Robert Brown
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Project Information


This two-year project is investigating whether grafting short-season watermelons onto cool tolerant rootstocks improves production in unheated high tunnels in Alaska versus their non-grafted counterparts.  In addition, the principal researcher is teaching methods of grafting that are applicable to most cucurbits to groups throughout Alaska with the intent of enabling or improving their production and increasing sustainability and crop diversity in a state that imports 95 percent of all of it's food.  Multiple methods of encouraging native pollinators to visit the growing area are being explored that have proven useful in the lower 48 states, but not in Alaska.  After the first year of growing (2017), there appears to be a statistically significant positive influence of grafting on fruit production and size.  2018 was a successful growing season, producing over 450 pounds of fruit, and the results will be presented in the final report.

Project Objectives:

The main objectives of the project are to test whether an interspecific squash x pumpkin hybrid rootstock can enable or increase watermelon production in an already cold tolerant and short season watermelon variety.  We also aim to teach methods that growers can apply to most Cucurbits, potentially increasing their production and availability in Alaska.  An additional objective is to assess whether it is possible to encourage native pollinators to establish nests near crops by building housing other SARE funded projects have recommended for native pollinators in the lower 48 states. 


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  • Dr. Carol Miles - Technical Advisor (Educator and Researcher)


Materials and methods:

First 2 graftings were 7 watermelon cultivars – Marmeladnyi (Tatiana’s Tomatobase), Blacktail Mountain (Seed Savers Exchange), Katanya (Baker Creek), Golden Crown (Osborne Seed Co.), Bozeman (Adaptive Seeds), Cream of Saskatchewan (Fedco Seeds), Small Shining Light (Seed Savers Exchange), and a variety supplied by another grower Alaska grafted onto Flexifort rootstock (Osborne Seed Co.). Damping- off (Pythium) disease occurred in the healing chamber. The source was potentially the seed of one of the watermelon cultivars that had been provided by a local seed producer. Disease samples were not sent to a lab for diagnosis (UA extension agent is no longer available in Anchorage so sample submission is not simple).  Rob had never experienced an outbreak of Damping-off at this level.  About 60% of the planting, about 350 plants, were lost. A third grafting was done on June 10 with two watermelon cultivars, Blacktail Mountain (Seed Savers Exchange) and Marmaladny (Tatiana’s Tomatobase), grafted on Tetsukabuto rootstock (Kitazawa Seed Co.). This was successful, 90% of grafted plants survived, and plants were transplanted to the high tunnel June 28.  Rob believes application of Bacillus amyloliquefaciens strain D747 (Trade Name Double Nickel 55) at grafting and once more 5 days later enabled successful graft healing and establishment.  


Seeds were sown individually in 606 cell packs inside Rob’s house.  Bottom heating was utilized with a temperature probe inserted into the soil and the temperature set to 83 F.  For germination, plants are started on shelves 12 inches below a bank of 4- 4 foot long T5 fluorescent grow lights that are each 54 watts and run for 16 hours each day. They are then transferred to a grow room, also inside Rob’s house (Fig. 1). Lights in the grow room are 1000 watt metal halide bulbs, and light is on for 14-16 hours. Air temperature is 75-80 oF and relative humidity is 35-40%.  The lights travel along a track which allows, Rob to grow more plants in the space.  He tries to average 1300 foot candles of light measured at the highest leaf surface.


Plants are grafted in an indoor room using Xacto knives, bamboo skewers, and clips (Fig. 2). Grafting method is hole insertion as Rob feels his fingers are not nimble enough to do the one-cotyledon method. Also, Rob feels the graft attachment is stronger with hole insertion, which he desires since his plants are grown on mounded raised beds.  On average, Rob will graft 325 watermelon plants in 1-2 days, and healing takes 9 days, and on day 10 plants are moved back to the grow room for 2-3 weeks prior to transplanting.


Healing is in a grow tent (50” X 50” X 79”; Milliard, New Jersey ) inside the house (Fig. 3). In the grow tent, humidity is provided by an ultrasonic humidifier (Vicks Ultrasonic Cool Mist, Procter & Gamble, Cincinatti, Ohio) set at 90% (+/- 5%) with a humidistat (Model RHC-R, Greenair Products, Boring, Oregon). Rob would like a fogger that provides more even humidity throughout the chamber, so that water does not condense and drip on plants. Temperature is set at 74-75 oF. Lighting is T5 single fluorescent tube, 4 ft that provides 350-400 foot candles (Sunblaster F54T5-HO). Plants are placed 2 shelves below the lights then as the plants are acclimated they are moved closer to the light source. Each day, the plants are moved backward and forwards and side to side under the light to try and attain equal coverage. Rob would like lights that are better suited for a wet environment, that provide better coverage over a wider area with less of a ‘spot light effect’.


Transplanting into the high tunnel on Rob’s farm was 29 June. The target date was the first week of June, but the first 2 graftings were not successful. A randomized complete block design was used for the experiment (Fig. 4). Rob had been measuring soil temperature at a 6 inch depth and tries to plant when soil temperature reaches 65F, but has since learned that a 2 inch depth is typically used and anticipates changing to this method in 2018.  This could enable even earlier planting.  Treatments include grafted and non-grafted plants of two cultivars. IRT Olive mulch (1 mil) covered the raised beds. Finished, on-farm-produced compost was added at 5 cubic yards per 1000 square feet.  Alaska Sea-Ag fertilizer (Analysis 5.4-9-.5 = ground bones from Alaskan fisheries, Palmer, Alaska) was added at 127.62 pounds per acre (1.875 pounds per 32 row feet).  Micronized Azomite trace minerals (Volcanic Ash deposit, Sanpete County, Utah) were added at 170.16 pounds per acre (2.5 lbs per 32 row feet).  Liquid fish fertilizer (Analysis 3-1-0, Foxfarm “Wholly Mackerel”, Arcata, California) was supplemented once when plants averaged 12 inches long and vines were running (tip of vine is pointed up 3” off ground) at a rate of 1 Tablespoon per gallon and each plant was given 1 quart. 


Plants were hand pollinated as it is difficult to attain consistent and reliable pollination by wild pollinators (Fig 5). Though Rob keeps European honeybees right next to his crops, he rarely observes them visiting flowers of the crops he grows and has not found them to be a reliable pollinator of anything but raspberries until the end of summer when the wildflowers in the mountains around his farm have finished blooming.  Pollination was done within a cultivar (there was no cross-pollination of the two cultivars in the experiment) before 10:30 am as Rob read this was the most successful time for pollination to occur.  With near 24 hour sunlight during the crucial pollination period, he is interested in exploring whether the flowers may be ready at other times, though he knows of no metric to do so other than trying it, which he feels is too risky within the scope of this project.  Hand pollination of watermelon is difficult and Rob appears to have had good success with his method. He says a critical quality of any watermelon variety to be grown in Alaska is that it produce female flowers early on.  Rob is working with Xerces Society to establish native pollinators (various Bombus species) around the high tunnel (Fig. 6). But even so, the tunnel is constructed and kept closed except during periods when his automatic exhaust fans cannot keep up to maximize heat retention as temperatures are generally low and unpredictable during the summer growing season (Fig. 7). The 2017 growing season was much cooler during the day than the previous two years, though night temperatures were slightly warmer due to cloud cover.  On 24 Aug. soil temperature in the watermelon plots was 60 oF (Fig. 8). The target for first pollination is the last week of June and for final pollination is the third week of July as fruit needs 50-60 days from fruit set to harvest in this climate. In addition to planting grafted watermelon on his farm, Rob also planted grafted watermelon plants in low tunnels at the Alaska Botanical Gardens (Fig. 9).   That location is used as a trial ground for varieties that are new to him.

In 2018, 6 plots of grafted and 2 plots of non-grafted Marmaladnyi watermelon plants were randomly installed in raised beds in the same unheated high tunnel as 2017.  The same parameters as 2017 were recorded.

Expected yield is 2 fruit per plant (Fig. 10). Number of all fruit that are greater than 8 inch diameter at time of harvest will be recorded. Only fruit that are close to full maturity will be harvested (tendril and leaflet at fruit connection to the vine are brown). Number and weight of harvested fruit per plot will be recorded. Brix will be measured for 2 fruit selected randomly per plot at time of harvest.

Research results and discussion:

The 2017 growing season was a difficult year for growing watermelons at the research site on multiple levels.  On top of the damping-off previously discussed which resulted in late plantings, the growing season at Rob's farm was much cooler during the day with less sunny days than the previous three growing seasons.  It is important to note that Rob's farm is some 1000 vertical feet above the city of Anchorage and lies in a narrow valley among hills and mountains.  It is common for clouds to be present or "backed up" in the mountains while much more sun reaches the lower Anchorage "bowl".   Rob finds this distinction valuable, however, because he feels that if he can successfully produce watermelons in this more adverse growing climate, then growers in the more sunny "banana belt" agricultural centers will also be able to.  Nonetheless, for the purpose of research, results were able to be obtained in 2017 that appear to be statistically significant and will be important contributions to the overall review of data after the 2018 growing season is complete (see attached Excel spreadsheet).  As previous research has shown, grafting watermelons varieties onto interspecific rootstocks does positively influence fruit production.  We know that one single limiting factor can limit or prevent plant growth and fruit production.  In Alaska, the most common limiting factors for watermelons are low soil and air temperature.  The use of rootstocks that are able to encourage fruit production in the presence of typically inadequate soil temperatures could be the "bridge" to successful and consistent watermelon production in southcentral Alaska.  In the first year of research, grafted watermelon plants significantly outproduced non-grafted watermelon plants.

2017-Grafted-Watermelon-Harvest-Spreadsheet-Rob-dec12 2017-Grafted-Watermelon-Harvest-Spreadsheet-Rob-dec121

In regards to encouraging native pollinators to visit and establish residence around the farm, results were not conclusive.  Out of 14 different homes he made for native bees, Rob had one that was occupied by yellow jackets only temporarily for a week and then abandoned.  However, in block nests, where different size holes are drilled in to a block of wood, Rob observed nearly all 1/16" diameter holes and been occupied by parasitoid wasps.  An examination of several of the cocoon nests revealed small, unidentified flies.  There were a total of 120 holes that had been filled with cocoons.  Rob is encouraged by these results because his garlic and onion crops are often damaged by onion maggots and the wasps may help him control them.  He had been worried that the wasps might be attacking his honeybees, but none were found in the nests he examined.  Rob utilized the University of Alaska's online portal to submit a picture of the wasp for identification and it was confirmed to be a parasitoid wasp by a Forest Health and Integrated Pest Management Specialist within the Alaska Cooperative Extension Service. 

The 2018 growing season was only slightly warmer than the 2017 growing season in Southcentral Alaska.  However, Rob had much more success in bringing his watermelon crop to harvest.  Plants were placed in the ground earlier and the high tunnel was vented at a higher temperature than in 2017.  This led to over 450 pounds of ripe watermelon being harvested.  Only one variety, Marmaladnyi, was grown in 2018 as it had proven to be earlier, more consistent, and more cool tolerant than any of the common varieties in the trade, including Blacktail Mountain.  Statistical analysis of the fruit weights are being performed and will be included in the final report.  It was obvious that grafted plants produced larger fruits.  Brix was measured, and though it was not run through a statistical analysis, fruits averaged around 11 Brix. 

The ripe fruits were taken to a local cider brewery, shredded, and pressed into juice.  The juice was combined with a sweet alcoholic apple cider in a 50/50 ratio and a drink was made from it.  However, the juice aroma were determined to not be appealing by Rob and the owner of the business after it was cooled and stored for a day.  A straw-like aroma appeared after only a day of storage, in addition to settling of solids within the solutions.  Rob determined the aroma was most likely due to certain enzymes breaking down the flavor.  Apparently this is a well-known problem and is the reason why so few real watermelon juice products are on the market.  The original hope was that since it is hard to compete with watermelon fruit prices in a city like Anchorage, that a value-added product would bring a higher price and allow the entire crop to be sold at once.  More study is warranted on making value added products.

The 2018 season has proven that it is possible to grow grafted watermelons in unheated high tunnels in Southcentral Alaska.  Watermelon is a species in the Cucurbitaceae family, and it may be extended that grafting of other species in the family that are currently hard to produce could also benefit from grafting.  Contributing to the base of growing knowledge in Alaska for future growers and indeed, for cool climate growers around the world has inspired Rob to continue research pursuits and investigation of grafting effects on other vegetable is currently being planned. 


Participation Summary
1 Producers participating in research

Research Outcomes

2 New working collaborations

Education and Outreach

2 Consultations
1 Curricula, factsheets or educational tools
2 On-farm demonstrations
5 Webinars / talks / presentations
2 Workshop field days

Participation Summary:

145 Farmers participated
20 Ag professionals participated
Education and outreach methods and analyses:

Taught a class at Alaska Mill & Feed on How to graft & grow watermelons in 2017.  Was a speaker at the Alaska State Master Gardeners' Conference and taught a room of 50+ growers and gardeners using the Powerpoint presentation.  Taught a 2 hour workshop at Alaska Botanical Garden.

In 2018, Rob gave a presentation at the largest garden club in Alaska, the Central Peninsula Gardening Club in Kenai, a 2.5 hour drive from Anchorage.  Over 80 people attended the 50 minute presentation.  Included in the discussion was a description SARE's Farmer/Rancher Grants and the audience was encouraged to apply.  Response was very positive as many people in the Kenai peninsula are partially or fully self-sufficient food growers.  He was asked back several months later to give a workshop.  The workshop filled up immediately and 20+ people attended a 2 hour workshop where they were able to not only learn about the theory and methods of vegetable grafting, but also had the opportunity to practice splice grafting tomatoes and hole-insertion graft muskmelon and watermelon.  Over 200 grafts were attempted and each participant received seeds to try in the 2019 growing season.

Work continues on processing data and we are hopeful to produce a journal article and factsheet in 2019. 

4 Farmers intend/plan to change their practice(s)
4 Farmers changed or adopted a practice

Education and Outreach Outcomes

65 Producers reported gaining knowledge, attitude, skills and/or awareness as a result of the project
Key changes:
  • Understanding principles of grafting vegetables

  • Belief that there is potential to increase production using grafting.

  • Measuring ripeness of watermelon fruit

  • New crops for growing in Alaska, including cool tolerant rootstocks, muskmelon, and watermelon varieties.

Information Products

Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture or SARE.