About Grafting
What are Grafted Vegetables?
Grafted vegetables are superhero vegetables: stronger,
bigger, faster, more able to fend off foes than regular vegetable plants
– and they deliver a more abundant harvest! Grafted vegetables are
created by attaching the top part of one plant (the scion) to the root
system of a separate plant (the rootstock). When their tissues heal,
they fuse into one Super plant with the best qualities of each: the
rootstock contributes vigor and disease resistance while the scion is
chosen for exceptional fruit flavor or quality. The resulting plant is
more vigorous and productive, going above and beyond the call of duty to
bring big, beautiful, wholesome harvests to gardeners everywhere.
Grafting Method
After experimenting with several methods, we decided to
use the Japanese top-grafting (or tube-grafting) method, a new technique
that is fairly simple but must be performed in carefully controlled
conditions to avoid stressing the vulnerable, freshly grafted plant. We
use a number of different rootstocks from Holland, according to which is
best suited to the scion variety’s growing habit and kind of fruit.
When both rootstock and scion have reached the ideal size, we sever the
seedlings, then use a special clip from Japan to attach the upper stem
and leaves of the scion to the lower stem and roots of the rootstock.
The stems must be the same diameter and shape so their vascular tissue
can align, remap, and reorganize, allowing water and nutrients to flow
up the stem.
Once the scion and rootstock have been clipped together, we place
them in a healing chamber which regulates temperature, humidity, and
light to create the best conditions for the vascular tissue to grow
together and the scar heal over. Over the next week or two, we slowly
reintroduce the seedlings to natural conditions. After another week or
two in the greenhouse, they are ready to be transplanted into the
garden.The graft is strong as nails once it is completely healed, but the plants must be handled carefully throughout the grafting process to avoid disturbing the graft union and ensure optimal conditions for the new plant to heal.
History of Grafting Vegetables
For centuries, grafting has been used in agriculture to
enhance the health, yield, and fruit quality of woody species like fruit
trees and grape vines. Large scale production of grafted vegetables
emerged in Asia, where land has been intensively cultivated for many
years. In the 1920s, growers there found that grafting watermelon plants
onto squash or gourd rootstock significantly reduced the incidence of
fusarium wilt. Today, 81% of Korean vegetables and 54% of all Japanese
vegetables (95% of Japan’s watermelons, oriental melons, greenhouse
cucumbers, tomatoes and eggplants) are produced on grafted plants.
Vegetable grafting is also popular throughout Europe, especially in
Greece, Spain, France, Italy, and Morocco.
In the U.S., the technique’s potential for improving
plant health and fruit yield without harmful pesticides, chemical
fertilizers, or soil fumigation/steam sterilization is catching the
attention of greenhouse produce growers and organic farmers, especially
on the East Coast with its short growing season. Together, the
environmental and economic benefits have made grafted vegetables a
worldwide movement among commercial produce growers.
Benefits of Grafted Vegetables
Advantages of grafted vegetables include enhanced plant
vigor, better disease resistance, tolerance of environmental stresses,
and heavier crops that are produced over an extended harvest period.
Disease resistance – This is probably the most important
reason commercial growers initially turned to grafted vegetables. After
Asian growers’ success with grafted melons in the 1920s, tomato
grafting emerged in the 1960s as a strategy to avoid soil-borne diseases
like bacterial wilt, which can be hard to eradicate in a tomato crop
because of its wide range of hosts and ability to persist for years in
the soil.
When a grower raises tomatoes and other solanums (potatoes, eggplant,
peppers) in the same fields or in the ground in greenhouses year after
year, a range of fungal, bacterial, viral, and nematode diseases can
become established in the soil, leading to a poorer yield with each
subsequent harvest. Grafting has been found effective against
verticillium wilt (Verticillium albo-atrum, V. dahliae), fusarium wilt
(Fusarium oxysporum), Fusarium crown rot, corky root rot (Pyrenochaeta
lycosersici), root-knot nematodes (Meloidogyne), bacterial wilt
(Ralstonia solanacearum), Tomato mosaic virus, and Tomato spotted wilt
virus.Grafting may also help plants ward off three other big tomato problems: early blight (Alternaria solani), late blight (Phytophthora infestans), and blossom end-rot (a physiological disorder caused by low calcium levels). Tomato plants that are less vigorous to start with or weakened by nematodes are more susceptible to early blight, so super-vigorous grafted tomatoes with enhanced resistance to pests and disease should fare better. Blossom end rot is exacerbated by fluctuations in soil moisture or when plants are stressed by drought. Grafted tomatoes, with their superior root structures, allow continued uptake of moisture and nutrients even in less-than-optimal conditions. It’s not clear whether grafted tomatoes are resistant to late blight (infamous for causing the Irish Potato Famine of the 1840s and still responsible for widespread losses of potato and tomato crops each year). The spores of the late blight fungus can’t survive in soil but are carried through the air, bypassing grafted tomatoes’ protective root system and landing directly on fruits or foliage. However, we expect that grafting would confer some level of protection because in general, the healthier and more vigorous the plant, the greater its ability to fight off a disease or pest. (See this article from Ohio State University for more research)
Tolerance of environmental stresses – Grafted plants are
also more tolerant of environmental stresses like salinity or
temperature extremes. Regular tomatoes often react to heat (temperatures
over 86 degrees Fahrenheit) by dropping their blossoms, but we’re
closely watching our grafted tomatoes to see if they can come through a
heat wave with flowers intact. And with the ability to withstand hotter
and cooler temperatures comes an added bonus – an extended growing
season. Cool-season gardeners should be able to set out plants a little
earlier in the spring and continue harvesting ripe fruits longer into
the autumn, while warm-climate gardeners who sometimes get tomatoes to
overwinter can increase their chances of winter and spring harvests with
hardier grafted varieties.
Increased vigor and yield – Even for those growers and
gardeners fortunate enough to have fresh soil and ideal growing
conditions, grafting has its advantages. The vigorous rootstock
increases the uptake of water and nutrients, for healthier and more
beautiful plants and greater harvests without using chemical pesticides
or fertilizers.
Overall, grafted vegetables lead to bigger harvests of
better quality fruits over a longer period with fewer harmful inputs.
All tomatoes can benefit from grafting, but heirlooms, which are
generally less disease resistant, can increase yields dramatically when
grafted on special rootstock. Organic farmers find that they can achieve
better resistance to pests and disease without soil fumigation or
chemical pesticides, as well as higher yields without chemical
fertilizers. Greenhouse produce growers are turning to grafted
vegetables because the plants thrive and produce even when crops can’t
be rotated frequently to fresh soil.