Mar 31, 2021Balance the costs, benefits of grafting
High tunnel production is popular for good reasons, but can be hampered by soil-based challenges such as disease, compaction, salinity and other types of stresses that sap overall productivity.
Grafting can help and creates a physical hybrid between two plants by attaching the top (shoot) portion of one plant to the root system of another to get the best traits of both plants.
Grafting has been important in tomatoes and watermelon and is gaining importance in peppers, cantaloupe, eggplant and cucumbers, but grower acceptance can be an issue.
It sometimes falls in a 2:1:1 pattern. “If I ask four growers about grafting, two will favor it, one will have a negative opinion, generally because of cost, and one is uncertain,” said Matt Kleinhenz, Extension specialist in Ohio State University’s Department of Horticulture and Crop Science.
Kleinhenz spoke on vegetable grafting in high tunnels at the most recent Great Lakes Fruit, Vegetable & Farm Market EXPO, held virtually in 2020.
Soilborne diseases are a leading reason for high tunnel growers to consider grafting. There’s strong evidence grafted plants offer the greatest return on investment to growers who are facing a serious soilborne disease.
“It has to be a disease for which a resistant rootstock is available,” Kleinhenz said. “There are many soilborne diseases in high tunnels. Grafting doesn’t address all of them.” There’s also the issue that not all scions react to the major rootstocks similarly, and some preferred scion varieties are more susceptible to disease and stress.
There are many rootstocks on the market – many with combinations or “packages” of disease resistance. The USDA-Specialty Crop Research Initiative Vegetable Grafting Project has tables of resistant rootstocks available as a resource for growers.
The tables compile rootstock information from companies who develop, market or distribute the rootstocks. The tables are available at www.vegetablegrafting.org/resources/rootstock-tables.
The tables are prepared by the Vegetable Production Systems Laboratory at Ohio State University. Rootstock varieties that help grafted plants tolerate extreme low and high temperatures, and overly wet, dry, saline or low fertility soils are being developed, along with rootstocks that enhance fruit quality.
The logic behind it
There are several reasons for adopting grafting.
Grafting can help enhance and maintain market presence when vigor and yield are very important. Restaurant and food service customers want a regular supply of a consistent quality.
Grafting can also be useful when single plantings are picked as many times as conditions allow – even if there is a smaller, early yield. “There are growers who are very keen on total, seasonal yield,” Kleinhenz said. High market prices can encourage grafting by offsetting the cost.
The size and nature of the operation is a factor. Small- to medium-size growers and organic growers were among the first to graft tomato plants for use in high tunnels. A small land base and having few other management options were the drivers.
Using grafted plants may also enhance the effectiveness of microbe-containing crop biostimulants. Grafting may also offset the lower yields frequently found in reduced-till systems. “In a very proactive, reduced till system, grafting may help, but how you use grafting will depend on economics and your situation,” Kleinhenz said.
What are the costs and what are the benefits of using grafted plants in your system? Will the higher production costs be offset by higher yields or higher prices from better quality? The economics of grafting vegetables vary by the farm.
Break-even analyses of using grafting are available from the University of Florida’s Institute of Food and Agricultural Sciences using its Vegetable Grafting Decision Support Tool. The tool calculates the threshold price or yield at which grafting and non-grafting production generates the same net return. The tool is available at www. graftingtool.ifas.ufl.edu.
It may also be possible to reach the same yield with a lower plant population of grafted plants than with non-grafted plants. This can change the economics.
Reaching the full potential of using grafted plants may require changes in management.
“Grafting may require significant changes in fertilization, irrigation and spacing,” Kleinhenz said. “If you don’t change management practices, you may not maximize the potential of the grafted plants.”
Positive production impact
The economics of grafting vegetables must be continually evaluated. The process can be complicated and there are pluses and minuses. “Grafting itself is a wonderful way to spread disease in a greenhouse because every plant is handled twice,” Kleinhenz said.
The number of suppliers of resistant rootstocks continues to increase. It’s becoming more common to find growers who’ve had a positive experience and have a positive outlook on grafting.
Evaluate grafted plants on your farm and perhaps especially if you use high tunnels, Kleinhenz said. There are issues and some risk, but grafted plants have the proven potential to make the most efficient use of high tunnels and generate the most value.
— Dean Peterson, VGN correspondent