December 2020 - 9

slipped onto the freshly cut rootstock
stem so that the top half of the channel
is left empty. Next, the scion seedling
should be cut at the same angle as the
rootstock seedling was cut. The top part
of the grafting clip should then be pulled
open slightly so the scion stem can slip
in. The cut surfaces of the two stems
should now be in perfect contact with
each other with no gap between them.
Tip #1: Start with good seed. Poor
quality seed can lead to bad germination,
increased risk of disease and inconsistent
seedling growth - all of which will make
grafting much more difficult.
Tip #2: Always run a small trial
before using a cultivar for the first time.
Sowing a few seeds and growing them
to grafting size can help to determine
the cultivar's germination rate, growth
rate and consistency.
Tip #3: Seed the rootstock variety two
days after the scion variety. Rootstock
cultivars have vigorous growth and,
therefore, grow faster and reach sufficient
stem diameter for grafting earlier than
scion varieties.
Tip #4: Choosing a transparent
grafting clip that is slightly smaller than
the seedling stem diameter will allow for
the union to be tight and will give more
visibility to the grafted area.
Tip #5: When making the cuts, it is
important to use a sharp surface such as
a new razor blade, recently sharpened
knife, or new grafting blade placed
on a grafting tool. Grafting tools are
commercially available and help to
ensure perfectly uniform cut angles.
Phase 3: Post grafting/healing
With the graft operation complete,
the next steps are to prepare the plants
for healing. The goal is to at first keep
the newly grafted plants at near 100%
humidity with low light. As the union
heals, the plants will slowly be acclimated
to lower humidity and higher light
conditions.
To begin, the grafted plants should be
placed onto a tray with drainage holes.
A second tray, without drainage holes,
should have a small amount of water
poured into it, but not enough to go
above the ridges in the bottom of the tray.
The small amount of water in this tray
will be a source of humidity and will
allow the grafted plants to have nearly
100% humidity during the healing
process. If the water does reach the
rockwool cubes then the water will be
wicked up, transpiration will occur in
the newly grafted plants, and the grafting
union will break.
Then, the tray of grafted plants should
be placed on top of the second tray,
making sure the water does not reach
the bottom of the tray with plants. Next,
a clear, plastic humidity dome should
be placed over the trays and the dome
and trays should be wrapped in plastic
wrap to prevent any humidity from
escaping. The sealed dome should then
be placed under a bench in the same
growth chamber where the seedlings
were grown.
It is important for the healing plants
to have some light, but if the light is too
strong it can heat up the leaf surface
causing transpiration and thus breaking
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the grafting union. By placing the plants
under a bench, a portion of the light
is filtered out so the healing plants get
approximately 60 μmol·m-2·s-1 for
16 hours/day leading to a daily light
integral of 3.5 mol·m-2·d-1. A shade
cloth could also be hung in the chamber
to the same effect.
After the plants have been kept under
these conditions for four days, it is time to
start acclimating the plants to the outside
environment. Four days after grafting,
two large lateral slits should be cut into
the plastic wrap where the dome and the
trays meet to start letting some of the
humidity out. One day later, the plastic
wrap should be removed and on the next
day the humidity dome should be cracked
open slightly to continue to acclimate the
plants to the outside conditions. On the
seventh day after grafting, the humidity
dome can be removed and the plants
can be moved onto the benches to
expose them to higher light levels. The
grafting clip will most likely have fallen
off by this point, but if it hasn't it should
be removed manually.
At this point, the plants should be
acclimated to the growth chamber
conditions and can now be transplanted
into rockwool blocks or larger pots.
Two weeks later, the tomato plants
will be ready to be transplanted
onto rockwool slabs (or into other
soilless media) and brought into the
greenhouse or high tunnel.
Tip #6: For larger-scale grafting
projects, a climate-controlled chamber
with a fogging system that can achieve
nearly 100% humidity can be used in
place of the humidity domes.
Tip #7: The trays and humidity domes
can be reused multiple times; however,
it is crucial to thoroughly wash and
sanitize them before reusing. Although
the grafting process can take some time
and effort to perfect, the team at Cornell
reports 95% to 100% success when using
these steps. In general, growers can save a
lot of money, greatly increase the quality
control, and learn a very useful skill by
grafting their own tomatoes.
Cornell University's Masaki Kurosaki,
Dylan Kovach and Neil Mattson also
contributed to this article. Go to
cea.cals.cornell.edu for more
information. VGN
VGN | DECEMBER 2020 | 9

http://cea.cals.cornell.edu http://www.Valent.com/Senstar http://www.valent.com

December 2020

Table of Contents for the Digital Edition of December 2020