The Effect of Healing Chamber Environments On the Survival of Grafted Eggplant, Watermelon, and Tomato

Successful grafting of vegetables requires high relative humidity for approximately one week following grafting to reduce transpiration of the scion material until rootstock and scion vascular tissue are healed together and water transport is restored. Although there is general consensus that high humidity is required for successful grafting of herbaceous plants, the effect of healing chamber environment on survival of grafted vegetable crops has not been systematically compared in temperate climates. The objective of this study was to evaluate the impact of three healing chamber environments on the survival of grafted eggplant, heirloom tomato, and watermelon. The experimental design was a randomized complete block replicated three times with 72 plants of each crop per treatment per replication. The three healing chambers included: 1.) a frame covered with plastic sheeting and shade cloth with a humidifier that misted plants for 20 seconds every five minutes (research design); 2.)  a frame covered with plastic sheeting and shade cloth misted every two days (industry design); and 3.) a frame covered with shade cloth (control). Three vegetable crops, ‘Epic’ eggplant, ‘Cherokee Purple’ heirloom tomato, and ‘Crisp’n Sweet’ triploid watermelon were self-grafted using the splice grafting technique, placed in the healing chambers for 7 days, and then acclimated over 4 days to ambient greenhouse conditions. Plants were evaluated daily for signs of wilting and graft failure for 14 days following grafting. Temperature was approximately the same for all 3 healing chambers (73-76^o F) while relative humidity levels varied (81% in Trt. 1, 86% in Trt. 2, and 42% in Trt. 3). There was no significant difference in tomato survival due to treatment, suggesting that tomato grafting can be successful with minimal healing chamber infrastructure and management. Although eggplant survival was higher in Trts. 1 and 2 (both 90%) than in the control (60%), this difference was not significant.  Watermelon survival in all treatments was low (splice grafting technique is not optimal for watermelon), although there tended to be higher survival in Trts. 1 (10%) and 2 (20%) than in the control (0). The larger goal of this experiment was to provide growers with information regarding effective and cost-efficient grafting healing chambers. A healing chamber with a humidifier has higher costs than the industry healing chamber and equivalent graft survival rates, suggesting that a humidifier is not cost effective for grafting in temperate climates.