Maximizing Production with Multiple Seeds Per Plug
The Tomato Magazine
By Lisa Lieberman
when processing tomato growers used
direct seeding instead
of transplants in their fields,
their planters would only allow
them to plant the seeds in small
groups instead of individually.
When the technology became
advanced enough where the
planters could dispense seeds
one at a time, growers soon realized that they
actually got more production from planting
multiple seeds per plug rather than singly. So,
they went back to planting multiple seeds—
usually between two and four seeds—per
plug to get maximum production.
Following this same logic—that using
more seeds per plug equals higher yields— researchers have
also begun experimenting with multiple-planting of transplants and
are fi nding that, in many cases, multiple
plants per plug can lead to signifi cantly
In processing tomatoes, transplants
originally became popular in the 1990s
in Woodland, Calif., when the processing
industry began following the lead of fresh
market tomato growers who were using
transplants in their fi elds instead of direct
seeding. In fresh market tomatoes, the
idea of using multiple plants per plug was
untenable because the goal is to produce
large-sized, aesthetically perfect tomatoes.In processing tomatoes, however,
the size and shape of the tomatoes doesn’t matter
compared with fruit quality and yield.
Processing growers were reluctant,
though, to try multiple plants per plug
because, at fi rst, it didn’t seem economically
feasible. The cost of growing multiple
plants in greenhouses would be higher. But
back in 2002, researchers began experimenting
with double and triple seeding of
plants in Colusa, Fresno and Yolo counties.
Although the double and triple seeding
didn’t seem to have any impact on yield in
Yolo County, researchers did see significant yield increases in Fresno
Even factoring in the zero yield gains in
Yolo County, the average yield increase per
acre in Colusa, Fresno and Yolo counties
was 1.4 tons per acre. In Colusa County,
which produced some of the best results,
there were yield increases of 10 percent in
double-seeded fi elds. Triple-seeded fields
had yield increases of 15 percent, Miyao
The upshot of all the test results was that
in six out of 22 trials using different varieties
of tomatoes around the state at various
times of the year, multiple-plantings per
plug resulted in signifi cant yield increases,
“Six out of 22 times is a little over 25
percent, which is statistically a significant
yield increase,” Miyao said.
Curly Top Question
In Fresno County, UC researcher,
Michele LeStrange did the experiment with
multiple-seeding. Her research, though,
wasn’t aimed at increasing yields. Her
focus was on using low populations of
plants in the fi eld — about 3,500 per acre — to see
if thinner stands of plants reduced
the incidence of curly top virus. Curly top
can be a problem in transplants.
Although LeStrange wasn’t able to test
her theory about curly top virus in low
stand fields, since there was none of the virus in her fi eld during
her trial, she did
find that multiple-seeding in thin tomato
stands increased yield seven out of 10
Jeff Karr, who works for TS & L Seed
Company in Huron, said that curly top
virus was also the reason many of his
growers got started double seeding plants
about fi ve years ago. Curly top infection is
caused by the beet leaf hopper which stings
tomato plants and spreads the virus.
“One of the reasons we started double
seeding was that it seemed that when beet
leafhoppers come into the fields, they
would sting one plant and then move on.
The virus isn’t contagious, so it’s not like if
one plant gets infected the one right next to
it gets infected, too,” Karr said.
In a sense, the idea of double seeding
was to spread the risk around the field.
If one plant got stung by a leafhopper,
chances were that the second plant
wouldn’t get stung also, he said.
“For counties south of Los Banos, we
noticed that with double seeding, most
yielded an extra one or two tons per acre,” Karr said.
Generally, it costs about $30 per
acre more to double-seed plants, Karr
explained, adding that if growers make $60
per ton on a ton of tomatoes, that’s a $30
profi t plus insurance against curly top.
“One hundred percent of our growers
use double-seeded plants,” Karr said.
One challenge in moving to doubleseeding,
however, is that it’s harder for
greenhouses to grow them. Plants tend
to compete with each other and put out
more vegetative growth. There are also
twice as many plants per square foot in the
greenhouse, which means that greenhouses
have to be more careful with their
fungicides, Karr said.
Miyao agrees that growing doubles in
greenhouses is a challenge.
“Since these plants are more
competitive in the greenhouses, they
have smaller stem diameters,” he pointed
out. “This is important in the field for
survivability. We hope, though, that by
using plant growth regulators we can
control plant growth in the greenhouses
and get shorter plants with wider stem
Ultimately, more work needs to be
done before researchers can make a general
recommendation that all growers use
The central question is why are we
seeing increases in yields in some fields
in Fresno and Colusa counties but not in
others such as Yolo? What’s so different
between Colusa and Fresno counties and
If you are inclined to take a gamble by
double seeding, it’s a little bit of a gamble
for a possible good payoff,” Miyao said.
© 2007 Columbia
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