Grafting Vegetables
Grafting is the process whereby the top of one plant (the scion) is attached via a graft union to the root
system of another plant (the rootstock). The most common objective of grafting is to overcome some
limitation of either the scion or the rootstock. For example, the root systems of many crops are
susceptible to attack by a range of persistent soil-borne diseases (Fusarium, Verticillium, Ralstonia) or
pests such as nematodes. If resistance to these pest problems can be identified in other cultivars or
even in closely related species it may possible to make crosses that introduce this resistance into the
pest sensitive crop. However this crossing process may take years and there are no guarantees of
success. A more rapid approach to accessing this pest resistance may be to simply use the pest
resistant material as a rootstock. A scion from a high quality, high yielding but disease/pest sensitive
cultivars is then grafted onto the resistant rootstock – effectively capturing the strengths of both the
high quality scion and the pest tolerant rootstock in a single plant.
Grafting has been used for centuries to improve yields and quality of a range of Horticultural crops –
especially long lived, high value crops such as grapes and tree fruit. While the potential to use grafting
to improve a range of vegetable crops has been long establish, commercial utilization of grafting in
vegetable crop production in North America has been limited – largely because of a questionable
cost/benefit relationship. However this situation is changing. In the past, vegetable growers
commonly used fumigation to control many of the most problematic soil-borne disease and nematode
problems. However the phasing out of methyl bromide and increasing restrictions on the use of other
fumigants is putting pressure on growers to find alternative means of dealing with these pest problems.
Using grafting as an alternative to pesticides also fits in with the growing interest in organic or pesticide
free production. Grafting may also increase the vigor of the crop, resulting in earlier or higher yields
and superior quality. By selecting appropriate rootstocks it may be possible to grow crops using less
fertilizer, water or other inputs. There is also the potential to employ rootstocks that will also improve
the crop’s tolerance of environmental stresses such as temperature extremes and excessive soil salinity.
Grafting has traditionally been done by hand – and is therefore most cost effective in situations where
high value crops are grown in areas with low labor costs. As a function of relatively low labor costs and
heavy pest pressure, grafting to improve pest tolerance, yields and quality of melons, peppers and
tomatoes is common across Asia. Higher labor costs, shorter growing seasons and lower pest pressure
have, to this point, restricted the use of grafting in vegetable transplants in North America. An
exception is the extensive use of grafted plants for greenhouse vegetable production in North America
– as the higher yields and quality of grafted plants can be recovered during the extended harvest period
available to a greenhouse grown crop.
The most common methods for grafting vegetables are the splice or tube graft, the tongue graft and
cleft method. Each grafting method has its strengths and limitations and some crops are more suited to
one grafting technique than another. Using compatible rootstock and scion material at the correct
developmental stage is critical to the success of any grafting operation. After grafting the plants need
to be kept in a mist chamber for a week or more to allow the graft union to heal over.
Published costs for producing grafted vegetables seedlings vary greatly – as a function of the efficiency
of the grafting operation, the basic cost of plant materials and labor costs. Grafting tomatoes by hand
increased the cost of each plant by 100 to 400% (Besri, 2003; Rivard et al., 2010). While the additional
cost associated with using grafted plants is substantial – the actual cost per unit area of using grafted
plants is comparable to the cost of fumigating (Kubota et al., 2008). This cost/benefit balance also
appears to be shifting in favor of using grafted plants – as the cost of fumigants is increasing rapidly
while restrictions on their use are becoming extremely stringent. With increasing grower experience
and economies of scale, the cost of production of grated vegetable seedlings will decline – especially if
efforts to develop and commercialize mechanical grafting systems prove fruitful.
Sources
Besri (2003). Tomato grafting as an alternative to fumigation in Morocco.
http://mboa.org/2003/012%20besrimgraftingmbao2003sd.pdf.
Kubota et al. (2008). Vegetable Grafting - history, use and current technology status in North America.
HortScience 43: 1664-1669.
Rivard et al. (2010). An economic analysis of two grafted tomato transplant production systems in the
United States.