Grafting of vegetable seedlings is a common practice – in Asian countries.
Here in North America, the practice is just getting a foothold, mainly
for greenhouse production.
Why graft? The idea behind grafting is to take a variety
with desirable above-ground horticultural characteristics (like fruit size,
flavor, etc.) and connect it to the roots of a variety with desirable under-ground
characteristics (like resistance to soil-borne diseases and vigorous root
growth.) Grafting vegetables follows the same principle as grafting fruit
trees, which has been done for a long time. In both cases the crop-producing
shoot is called the scion, which is removed from its original roots and
placed onto a new plant, called the rootstock.
Among greenhouse tomato growers, grafting is quickly being adopted
as a way to manage root diseases and increase fruit production. Organic
growers in particular can gain from grafting because growing tomatoes in
soil and compost rather than in sterile media often leads to problems with
weak roots, as a result of soil-borne pathogens.
Varieties for grafting. In my neck of the woods, growers
have a wide range of preferences for varieties of greenhouse tomatoes,
depending on their markets and production systems. Popular greenhouse varieties
include Trust, Cobra, Buffalo, as well as cherry, cluster and even heirloom-types.
All of these have been used as scions. There are far fewer tomato varieties
that make sense to use for rootstock. The two most common are ‘Maxifort’
and ‘Beaufort’. Both of these have tolerance to some common soil-borne
diseases. ‘Maxifort’ also results in very vigorous growth while ‘Beaufort’
leads to a more moderate increase in plant vigor. These increases in vigor
can be seen in both above ground-ground and below-ground growth.
Types of grafts. Two common grating techniques are top
grafting and side grafting. With top grafting the scion is completely cut
off from its roots and placed on top of the rootstock stem. Side grafting
involves making a partial cut into the stem of the scion plant and then
inserting the cut-off stem of the rootstock into that cut. The seedling
is then allowed to retain both set of roots until the graft with the new
Top grafting relies on a tiny plastic tube or sleeve to hold the
scion and rootstock together until the graft heals. Top grafting is quicker
and bit less complicated to do than side grafting because it requires only
a single complete cut through both the root and shoot portions of the graft.
This technique can be used on very small seedlings.
Side grafting takes a little longer but is preferred by some tomato
growers because it is a bit more forgiving. If greenhouse conditions for
graft healing are less than ideal, the grafted seedling still has its original
set of roots to help during the transition. Side grafting can also be done
with seedlings that have become larger than is ideal for top grafting.
And, side grafting seems to accommodate a bit less uniformity between scion
and rootstock stem diameters than is the case with top grafting, where
the two stems must be almost exactly the same size. A small clip, much
like an office binder clip, is used to hold side-grafted plants together
until they heal.
Starting the plants. Rootstock varieties tend to have
long thin stems so they are often sown a few days earlier than seed for
the scions. Some growers will make sequential seedlings of the rootstock
over several days to assure that they have the right selection of plants
size to choose from when grafting. There is a narrow range of plant size
for grafting. The ideal is when the stems are about 2 mm in diameter for
top grafting, and 2 to 3 mm for side grafting. (Depending on conditions,
plants this size usually have 4 or 5 true leaves showing.) It’s physically
difficult to graft plants that are thinner than this, and the success rate
declines rapidly as the stem diameter increases.
Top grafting. Start by selecting healthy scion and rootstock
plants that have the same stem diameter. Then remove the first set of true
leaves on the scion to reduce transpiration during the healing process,
leaving only the uppermost couple of leaves. Leave the cotyledons in place.
Next, cut off the scion from its roots just below the cotyledons, at about
a 60 degree angle.
Now take the rootstock, and cut off the top just below the cotyledons,
at exactly the same angle as the scion was cut. (If the plants are too
small the cut can be made above the cotyledon but be sure to prevent these
suckers from growing later.) Slip the grafting sleeve onto the rootstock
stem and gently push in the scion stem so that the cut surfaces make full
contact. Wiggle gently if needed. Place transplant into a large cell tray
(72s) or small individual pot and water promptly.
Side grafting. With this method, larger seedlings are used,
typically two to three weeks old, since the stem diameter must be large
enough to perform the graft. First, select a pair of healthy plants with
similar stem diameter. Then remove the cotyledons and the first true leaves
on the scion. Make an upward cut that goes two-thirds of the way
through the scion stem at a 60 degree angle, about an inch below where
the cotyledons were.
Then take the rootstock, and cut off the top just below the cotyledons.
About an inch below that make a downward cut in the remaining stem that
matches the cut in the scion: two-thirds of the way through, at a 60 degree
After the matching cuts are made insert the rootstock stem up into
the scion stem, and clip the plants together using the small side grafting
clip. Hold the two root balls together and transplant into a small pot,
The side-grafted roots of the scion are left intact for 4 to 5 days
while the graft union heals. Then it’s time to sever the stem connecting
to the original scion roots, so that the plant will rely only on the desired
rootstock. An initial cut should be made part way through the stem to ‘wean’
the plant and reduce the shock of removing the original roots all at once.
At this time it helps to stabilize the plants by attaching them to small
stakes. After 2 more days, the stem to the scion root is cut all the way
through. Leaving both root systems in place, rather than removing the scion
roots, is not recommended as that may enhance the population of root pathogens
which can thrive on the more susceptible roots.
Post-operative care. After grafting keep the plants
where it’s warm (80-85 degrees F) and at least 95% relative humidity while
the grafts heal. They should be held in a heavily shaded area, like under
a bench, and misted enough to maintain the humidity, but not more. (The
leaves don’t need to be wet all the time, this will reduce success.)
It takes about 4 to 5 days for top grafts to heal, and 6 to 7 days
for side grafts. Placing plastic domes over trays of top-grafted plants
appears to enhance success. For a couple of days before setting the grafted
plants out, gradually increase their exposure to direct light by pulling
them out from under benches or removing any covering for a few hours early
or late in the day. If using plastic domes, prop them open during this
When you eventually move the plants completely out of cover mist
them if needed to prevent wilting. Finally, when setting plants in the
production house be sure that the graft union is above the soil line. If
the scion roots into the soil, the plant will be susceptible to soil-borne
Managing plant vigor. Because grafted plants are more
vigorous, they will produce a lot of vegetative growth at the expense of
reproductive growth, in other words, too much foliage and not enough fruit.
So, you have to take steps to reduce plant vigor. This may take some getting
used to, especially if you’ve previously been trying to promote vigor in
your un-grafted plants.
Leaf removal is one way to reduce plant vigor. Removing leaves may
feel counter-intuitive, but apparently only 10 to 12 fully expanded leaves
are needed to do the job of capturing sunlight to feed a grafted greenhouse
tomato plant, at least in the Northeast. Allowing more leaves than that
sure looks nice and lush, but it seems to suppress fruiting.
Another way to suppress the vigor of grafted plants is to let them
develop two leaders, or main stems, rather than the single stem that’s
customary in greenhouse production. This also reduces the number of grafted
plants that you’ll need by half. The double-leader system adds a ‘load’
to the roots, and that suppresses vigor sufficiently so that only ‘normal’
leaf removal is needed. By that I mean taking off all the leaves below
the lowest cluster with maturing fruit.
There are a couple of ways to get a double leader. One is to cut
off the top of the plant soon after the graft heals so that two equal-sized
leaders will be produced from the buds at the base of the cotyledons. This
technique works well with top grafted plants. Of course, it will set back
the plant, delaying first fruit harvest date by about a week. Alternatively,
you can allow the main stem to grow normally, but then let the sucker below
the first fruit cluster develop to become the second leader. Since this
leader develops later, it will be shorter than the main stem, which can
lead to shading. To prevent that from happening, when trellising the crop
the main stem can be angled to the side to allow the sucker to grow straight
up and eventually catch up, resulting in double leaders of equal size and
With ‘Maxifort’ rootstock a double leader is recommended. ‘Beaufort’
is a good rootstock for a single leader plant because it is not as vigorous.
When using the double leader system don’t forget to adjust plant spacing
accordingly, so that each grafted plant has the growing area of two ungrafted
or single leader plants.
Tips for success. Expose seedlings to full sun and some
water stress before grafting to keep the plants short and increase tolerance
to water stress. Avoid excess fertility in your potting mix so that plants
are not too lush. Shortly before grafting, make sure plants have been watered
and are not wilted. Make grafts early or late in the day to avoid water
stress. If you can, do your grafting on cloudy days. Graft in a location
that’s protected from direct sunlight and away from greenhouse heater discharge.
Don’t cut more plants than you can graft together in a few minutes, so
the cut surfaces do not dry out. Always match scions and rootstocks of
equal stem diameter, cut them at exactly the same angle, and make sure
the cut surfaces make good contact when the plants are clipped together
so that they have the best chance of successfully connecting to each other.
For more information you can order a CD with a 20-minute video featuring
Mike Collins, an organic grower who’s been grafting for 15 years. Send
your request with $10 payable to UVM to: University of Vermont Extension,
11 University Way, Brattleboro VT 05301. Also see articles on grafting
greenhouse tomatoes by Richard McAvoy, Univ. of Connecticut at: extension.umass.edu/floriculture/fact-sheets/grafting-techniques-greenhouse-tomatoes and
by Jack Manix of Walker Farm at: www.newenglandvfc.org/2003_conference/proceedings_03/tomato/tomato_grafting.pdf.
Grafting clips and rootstock varieties are available from: Johnny’s
Selected Seeds www.johnnyseeds.com and Hydrogardens www.hydro-gardens.com.