Grafting Vegetables Isn’t Effortless, but Could be Advantageous

Southwest Yard & Garden by Dr. Marisa Thompson

Grafted tomato plants with silocone graft clips holding the scion (top) to the rootstock stem (photo credit wikicommons).  

 Question:

Other than the novelty, why would a gardener be interested in grafting vegetable plants?

-        Yours Truly, Los Lunas, NM

Answer:

I’ve been hearing more and more about vegetable grafting for commercial production and wanted to know more, so I posed this week’s question myself.

Grafting, in general, is a common method for propagating plants by carefully joining cut plant parts so they grow together as one plant. Many plants can be propagated from seed or from cuttings that put out new roots. Others—like apples—don’t “grow true’” from seed or root easily from cuttings and must be grafted. Every apple you’ve ever eaten is from a grafted apple tree (unless you’ve eaten crabapples) where a small branch cut from a desirable apple tree was then grafted onto the trunk of an apple variety with desirable roots. “Desirable” means different things depending on if you’re talking about the top portion (scion) of the grafted plant or the bottom (rootstock). Desirable scion traits might include flowering time, fruit flavor, or branching pattern. Desirable rootstock traits could involve rooting vigor, disease resistance, or salt tolerance, depending on local factors.

In much of the woody plant realm (i.e., most fruit trees and many landscape perennials), grafting is standard, even though grafting is expensive because it takes skill and time. Even with perfect growing conditions and skillful technique, the graft may not “take,” for example, if the cut edges of the two plants are not lined up properly, or a pathogen infects the tissue. The costs of grafting are reflected partly in the high sales prices on fruit trees and other grafted specimens. But these plants are expected to live year after year (hence, “perennial”) and there may be an added benefit if growing from seed or cuttings is not an option.

So, grafting makes sense for some perennial species. Now let’s consider vegetable plants, like tomatoes or watermelons, which are grown as annuals, meaning they complete their entire life cycle in one growing season. Grafting is also expensive in the vegetable crop world. Understandably, grafting vegetables is not very common in New Mexico vegetable production. You won’t likely find vegetables at local farmers markets here that were harvested from grafted plants. That’s partly because direct-seeding row vegetable crops can be more economical than transplanting. Grafting after plants are in the field is not a viable option because they need serious babying (high humidity and low environmental stressors) for the grafts to take successfully. At a horticulture conference last week, Dr. Brian Ward, Organic Vegetable Specialist at Clemson University, gave me a quick grafting demo. With his permission, I videotaped the tutorial. 

Dr. Ward provided a great example of how vegetable grafting becomes advantageous when a soil-borne disease is known to devastate the roots of a desired variety of, in this case, watermelon, but another watermelon variety makes good rootstock because it develops roots that are resistant to that same disease.

If better rootstocks aren’t an option, disease issues in New Mexico will not be remedied by grafting. Other ways that grafting might benefit our vegetable growers include improving plant salt tolerance, cold tolerance, water use efficiency, or nutrient use efficiency. Can you see now why this trend is growing and how important experimental research is in this field? At http://www.vegetablegrafting.org/, a research-based information portal, you can tap into research and education programs being conducted all over the world. As a home gardener, you too can experience the pros and cons of grafting vegetable plants. It’s tricky to be sure, but you just might be able to bask in the “grafterglow” of success.

Send gardening questions to Southwest Yard and Garden - Attn: Dr. Marisa Thompson at desertblooms@nmsu.edu, or at the NM Desert Blooms Facebook page (@NMDesertBlooms)

Please copy your County Extension Agent (http://aces.nmsu.edu/county/) and indicate your county of residence when you submit your question!

For more gardening information, visit the NMSU Extension Horticulture page at Desert Blooms (http://desertblooms.nmsu.edu/) and the NMSU Horticulture Publications page at http://aces.nmsu.edu/pubs/_h/.

Marisa Y. Thompson, PhD, is the Extension Horticulture Specialist, in the Department of Extension Plant Sciences at the New Mexico State University Los Lunas Agricultural Science Center, office: 505- 865-7340, ext. 113.