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Researchers weigh in on plasticulture strawberry research
BEN PHILLIPS
ANNIE KLODD
Michigan State University
University of MInnesota
COURTNEY WEBER
Cornell University
Plasticulture strawberries have been
a topic of discussion over the last
couple years in Michigan. In a recent
Vegetable Beet podcast episode, we
discussed it for about an hour with
Courtney Weber, small fruit breeder
at Cornell University, and Annie
Klodd, Extension fruit specialist at
the University of Minnesota. Brad
Bergefurd, at Ohio State University,
has been researching annual
plasticulture strawberry production
for Ohio conditions, and also
contributed insights.
June-bearing strawberries are
traditionally grown perennially in a
" matted-row " system that uses straw
for winter protection and weed control
between the rows. This system relies on
daughter plants produced from runners
each year to create 12 rows 18 inches
apart for fruit production in the following
summer. Some northern vegetable
growers are experimenting with a
modified plasticulture strawberry system
where bare root June-bearing plants
are hand-set in the spring on plastic.
Unfortunately, this results in an entire
season's worth of runner control through
the first summer. Also, plants seem to die
out faster over winter, and the earliness
that sometimes comes with plasticulture
is hampered by spring freezes.
So, what do you do?
Runner production can be reduced
in plasticulture strawberries by
planting later in the summer so that
there are fewer long-days left in the
season to trigger runnering. In zone 5b
and north, the best planting time for
this is in mid-July to mid-August. So,
then the question is, how to get plants
in the middle of summer?
The annual plasticulture system
as described in the production
guide from Nourse Farms (www.
noursefarms.com/resources/pdfs/
plasticulture/plasticulture.pdf) uses
dormant bare-root plants that are dug
in the early spring and refrigerated
until planted into plastic in June and
July. Unfortunately, plant quality can
suffer with prolonged refrigeration,
producing mixed results. In the South,
plug plants produced from harvested
runner tips are planted in the fall for
the following spring crop. However,
plugs are generally not available until
the end of August or early September
and usually of varieties not commonly
grown in the north. This is OK for
growers in zones 6-7, but too late for
zones 4-5. In these areas, fall planted
plugs are unlikely to generate enough
12 | VegetableGrowersNews.com
A planting of a plasticulture strawberry crop. Photo: North Carolina State University
crown branching or flower bud
development for an acceptable crop in
the following spring.
A hybrid system has been used by
some growers in the north utilizing
what is being called a " crown plug. "
About six weeks before the target
planting date, growers prune the roots
of dormant bare-root strawberries,
place the remaining crown into 2-inch
50-cell plug trays, and grow them in
a greenhouse or pot-lot. This allows
better control over plant quality and
planting date, a better selection of
northern-adapted varieties in plugs,
and a more efficient system for
removing flowers and early runners
because all the plants are concentrated
in one area in trays. However, this
system has not been commercialized
by tip and crown producers, and a
grower would need to do this on
their own or collaborate with a local
greenhouse to receive the bare-root
plants and raise them. Plug plants can
also be planted using a mechanical
transplanter more effectively than bare
root plants.
Even with later planting, you will
still need to clean up runners at least
one time in the field before winter
protection goes on. Aside from hand
pruning, some growers are using
Apogee growth regulator, though
reports have varied on its effectiveness,
and some varieties seem more reactive
to it than others. Some growers are
using a contact herbicide like paraquat
(Gramoxone) or pelargonic acid
(Scythe) to burn off runners once they
get long enough to be out of the way of
the mother plants on the sides of the
mulch bed.
Can you realistically expect a
perennial system out of plasticulture
strawberries? Experience suggests
you should only expect one harvest
season, or one additional carryover
winter after the first winter at most.
Each year, more crowns are made by
the mother plant, which loosely align
with the number of trifoliate leaves the
plant makes. In a matted-row system,
the mother plant produces branch
crowns too, but also makes daughter
plants on runners that root nearby.
These daughters make the biggest fruit
and bear the bulk of the production in
the following year.
However, in a plasticulture system
where only the mother plant is
maintained and the potential daughter
plants are removed when the runners
are cut, production is left to just the
branched mother crown. This results
in a reduction in fruit size as the ten
or more branch crowns produce a
multitude of flowers all competing for
resources from a single root system.
Additionally, as the mother plant
grows, the crown extends further
out of the ground, making it more
susceptible to winter injury.
Thinning crowns with a shovel
has not proven very practical, and
exposed crown tissue is still an issue
in winter. Despite this, some growers
are shooting for three and four years
on plastic by dividing and digging out
crowns to thin the stand manually,
installing windbreaks, and covering
with more fabric to try to protect taller
crowns in winter. All these strategies
increase labor and costs, but only
marginally forestall the decreasing
fruit size and yield.
Many growers in Ohio have adopted
plasticulture strawberries, with some
growers attempting one additional
carryover season by keeping plants
mowed after the last harvest and then
only irrigating and fertilizing enough
to keep them in a sort of summer
dormancy. Then they turn on the
irrigation and fertilize again in August
to grow out the plants into the fall and
control runners at least once.
So, why not do strawberries
annually, like most other vegetables?
This is the most common way of
growing strawberries in the U.S., with
the Midwest being the hold out with
matted-row perennial production.
Annual strawberries are basically like
growing garlic, where you would plant
in one year and harvest in the next.
Cost is one big factor. Plugs plants are
more expensive than bare roots, and
the planting density is higher to make
up for the lack of daughter plants.
So, it's tempting to spread that cost
over several years. You may be able
to increase yield per plant by pushing
them hard in the fall of the first year to
produce multiple branch crowns, with
the expectation of one harvest instead
of carrying them over. This would
entail using row cover or low tunnels,
depending on your timing or interest
in earliness in the spring. You could
also double, triple, or quadruple-crop
the plastic with other vegetables.
Michael Kilpatrick, at The Farm on
Central, in Carlisle, Ohio, plants two
rows of strawberries per plastic bed in
August, and also a third middle row
of fall-harvested lettuce, and then in
the spring puts garlic cloves in those
empty lettuce holes as early as possible
for a " spring garlic " harvest before
strawberries take off. After harvest,
other Ohio growers spray off or yank
and flip the old strawberries from
their holes so that they are uprooted
but serve as a mulch, and then plant
a competitive sprawling plant like
cucumbers or pumpkins in the middle
holes. Talk about value per square foot
over time!
For field reports on annual
plasticulture strawberry research
conducted in Ohio visit
https://southcenters.osu.edu/
horticulture/fruits/strawberries. VGN
http://www.noursefarms.com/resources/pdfs/ https://southcenters.osu.edu/ http://www.VegetableGrowersNews.com
August 2021

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