Winter 2023 - 14

FROST CONTROL
Moving to Plan B, she bought some propane and her
daughter planted peas on Jan. 16 for a spring crop. The
peas grow on a netting trellis down the middle of the
tunnel, with celery planted at the edges. Walsh also plans to
put in tomatoes early, to precede the summer market glut.
Unfortunately, crop plants are not the only creatures
that thrive in the warmth of the high tunnel. Field rats
find the tunnel edges appealing, especially if plants and
debris provide good cover. They like to nibble the pea
and cucumber plants.
Walsh discourages the rats by removing debris,
keeping the ground open so her cat and dog can deter
the rats, and pre-sprouting the peas to give the pea
plants a head start.
Walsh is careful to not irrigate too much inside the
tunnels, as too much water encourages fungal growth.
Beyond that, she finds that the scarcity of insect pests
makes winter production easier. For this reason, planting
peas in the heated tunnel in autumn works better than
planting them in spring.
Walsh gladly passes on her winter production and other
farm knowledge to others, offering tours to visitors and paying
teenage interns to learn the ropes by working on the farm.
Seventy-five miles to the northeast, Flow Farm owner
Mark Epstein recently installed a " climate battery "
greenhouse. The design was developed at Threefold Farm
in Pennsylvania.
The " battery " refers to storing heat in the soil. To create
the battery, last spring the footprint of the future 96-foot
by 36-foot tunnel was dug down to 8-foot depth, creating
a large hole with a mountain of dug-out soil nearby.
Four vertical air intake manifolds, extending upward to
2 feet above ground, were added to one of the long sides:
one at each end and two in the middle. A fan was installed
at the top of each intake manifold to draw indoor tunnel
air into the soil. Two output manifolds were installed on
the opposite side of the tunnel, about one-fourth of the
way from each end of the tunnel.
From each intake manifold, seven corrugated-plastic
tubes were laid horizontally, extending across to one of
the output manifolds. Tubes from two intake fans lead to
each output manifold. Only one of the seven tubes goes
directly to the output manifold; the others are in pairs that
bulge outward at increasing distances before coming back
together at the output manifold, like the lines in an onion.
The tunnel footprint was then filled in with 2 feet of
soil. Another set of horizontal hoses was placed at 6-foot
depth. The process was repeated depths of 4 and 2 feet
as well. Each output manifold thus has 56 tubes, 28 from
each of two intake manifolds. The tubes are porous but
covered with a " sock " so that air diffuses but soil cannot
block the pores.
Once the floor of the tunnel was filled with soil to
surface level, the high tunnel was constructed. The
underground tubes now spread warm daytime air
throughout the soil under the entire high tunnel to a
depth of 8 feet. The air warms the soil. At night, the fans
push air out of the warmed soil.
With this system, using much less energy than burning
propane, Epstein has kept the tunnel at 40⁰ F or higher,
even when the outside temperature plummeted to 10⁰ F
on Christmas Eve.
Electronic sensors and controls enable Epstein to use
a smartphone app to set the temperatures at which the
fans turn on and off and to monitor the temperature at
several sites in the tunnel. At one point, the temperature
dipped below the set point of 40⁰ F, so he checked and
found some 1-inch gaps in the wall of the intake side of
the tunnel. Once the gaps were fixed, the temperature
was under control again.
Walsh and her husband, Will Zabel, in a high tunnel at DabHar Farm.
Photo: Phyllis Walsh
In addition to keeping the tunnel above 40⁰ F in winter,
the climate battery, with some misting, keeps the tunnel
below 90⁰F in summer. Within this temperature range,
Epstein can grow tropical and subtropical plants such
as citrus and avocado trees and pineapples along the
left side of the high tunnel. In the center, he has grown
three rounds of cover crops since the tunnel was built last
spring, but soon he will keep the central area planted in
annual vegetable crops such as tomatoes and cucumbers.
The right side is lined with work benches for starting
seeds. Heat mats help keep the seedlings warm. The large
upfront investment in building the climate battery high
tunnel is now providing a perfect environment for growing a
variety of organic crops, with only low energy requirements
for running the fans, heat mats, and water pump.
14 WINTER 2023
Winter 2023

Table of Contents for the Digital Edition of Winter 2023
