High tunnels are covered structures that provide a protected environment that extends the growing season and allows growers to capture premium prices through improved yield and quality. High tunnels rely on passive heating and cooling, which means temperatures inside the tunnel can increase rapidly on sunny days and cooling the high tunnel is largely done through venting or opening the sidewalls and end walls. Tomato is one of the most valuable high tunnel crops per square foot (Galinato and Miles 2013) and its production continues to increase along with the interest in high tunnel production (Janke et al. 2017). This can be partially attributed to financial assistance provided by cost-share grants such as the Natural Resource Conservation Service (NRCS) Environmental Quality Incentives Program (Ernst et al. 2020; Janke et al. 2017). The NRCS incentives program has led to more than 1,500 high tunnels constructed in Kentucky (Deena Wheby, NRCS, personal communication. Though high tunnels are high-value infrastructure, providing many production benefits, they can also create a multitude of challenges for growers through increased soil temperatures, soil fertility degradation from intensive production, increased soil salinity, and lack of crop rotation and sanitation.

The practice of combining a hardy, disease-resistant root system (called the rootstock) with a desireable aboveground fruiting body (called the scion) is called grafting. Tomato grafting can result in increased marketable yield, fruit weight, and crop vigor, compared to non-grafted plants (Frey et al. 2020). The main objectives of using grafted rootstocks are to increase resistance to soilborne diseases and root-knot nematodes, increase fruit yield and quality, and better adapt crops to harsh environments (Kubota et al. 2008). In a two year on-farm experiment conducted in Kentucky, grafted tomato plants produced 38% higher yield compared to non-grafted tomato plants (Bajek and Rudolph 2023). An average healthy non-grafted determinate tomato plant can produce approximately 25 pounds of fruit. A 38% yield increase would result in 9.5 pounds of additional fruit per plant. With the average price per pound of tomato being $2.50, this can result in a nearly $24/plant additional profit. Approximately 400 tomato plants can be grown in one 30 x 96 ft high tunnel. If all plants were grafted, this could result in $9,500 of additional profit for the grower.

Grafted plants can be purchased, but there are limited companies offering this service and the cost depends on the rootstock and scion combinations. Grafted plants can cost anywhere from $2.50 to $5 per plant plus shipping. However, growers can graft tomato plants themselves and potentially save 50% of costs. If there are 400 plants in one 30 x 96 ft high tunnel, one grower could save between $500 to 1,000 before planting. 

Two hands-on grafting workshops were led by Dr. Rachel Rudolph, Extension Vegetable Specialist, in the spring of 2023 to train growers on tomato grafting methods. All participants were able to practice grafting at least four plants and could take those plants home. The workshops were free for all to attend. There were a total of 33 participants at both workshops, which also included county Extension agents. In pre-workshop surveys, 84% of respondents indicated “I know nothing” or “I have heard a few things about grafting” when asking about their current knowledge of grafting. Ninety-one percent of respondents had no prior grafting experience. After the workshops, 50% of participants rated their confidence in being able to graft their own plants at “pretty confident” and 28% “very confident.” Overall, there was a 58% increase in knowledge after the workshops. When asked how likely they would be to start grafting their own plants, 53% of participants indicated they were “very likely” or “definitely going to graft.”

The grafting workshops educated growers and county Extension agents on the benefits of grafting and provided time and instruction for participants to practice grafting on their own. If 18 of the participants from the workshops followed through on their plan to start grafting tomato plants, this could result in $171,000 of additional income to Kentucky growers in one season.

Literature Cited

Bajek V, Rudolph RE. 2023. Managing southern root-knot nematode in Kentucky high tunnels using grafted tomato. HortScience 58(6):704-713. https://doi.org/10.21273/HORTSCI17141-23 

Ernst M, Woods T, Butler A, Wolff B, Jacobsen K. 2020. High tunnel production and marketing survey: data summary. Univ Kentucky Coop Ext Serv Bul. CCD-SP-17. https://www.uky.edu/ccd/sites/www.uky.edu.ccd/files/HTsurvey.pdf

Frey CJ, Zhao X, Brecht JK, Huff DM, Black ZE. 2020. High tunnel and grafting effects on organic tomato plant disease severity and root-knot nematode infestation in a subtropical climate with sandy soils. HortScience. 55(1):46-54. https://doi.org/10.21273/HORTSCI14166-19.

Galinato SP, Miles CA. 2013. Economic profitability of growing lettuce and tomato in western Washington under high tunnel and open-field production systems. HortTechnology. 23(4):453–461. https://doi.org/10.21273/horttech.23.4.453.

Janke RR, Altamimi ME, Khan M. 2017. The use of high tunnels to produce fruit and vegetable crops in North America. Agr Sci. 8(7):692-715. https://doi.org/10.4236/as.2017.87052.

Kubota C, McClure MA, Kokalis-Burelle N, Bausher MG, Rosskopf EN. 2008. Vegetable grafting: history, use, and current technology status in North America. HortScience. 43(6):1664-1669. https://doi.org/10.21273/hortsci.43.6.1664.