June 2021 - 42

technically speaking
BY ERIK RUNKLE
Challenges of Growing
Vertically in Greenhouses
The vast majority of greenhouse crops
are grown on a horizontal plane, either on
benches or floors. There are exceptions,
though, for both ornamentals and high-wire
vegetable crops. For example, growers of
ornamentals commonly produce baskets of
annual bedding or foliage plants that are hung
overhead. While this allows crops to be grown
in two (or sometimes more) layers inside a
greenhouse, the planted containers shade
crops below. Growers of vine crops
such as tomato, pepper and cucumber
also grow vertically to maximize use of
greenhouse space.
Vertical farming usually refers
to the production of crops indoors
in multi-stacked layers with LED
lighting. As this emerging industry
continues to expand, there is
also interest in vertical farming in
greenhouses, especially for edible
crops such as leafy greens and herbs.
There is a wide range of vertical
farming approaches for greenhouse
cultivation, with various degrees
of sophistication, including use of
towers, fixed shelving and rotating
Erik Runkle is
professor and
floriculture Extension
specialist in the
Department of
Horticulture at
Michigan State
University. Erik can be
reached at runkleer@
msu.edu.
racks (Figure 1). However, there are challenges
when growing vertically in greenhouses, some
of which cannot easily be overcome.
Light intensity and uniformity. One of the
reasons we grow crops horizontally inside
greenhouses is to maximize plant capture
of sunlight. At least in temperate climates,
greenhouses are usually oriented so shadows
inside move as the sun moves each day from
the east to the west. The combination of a
horizontal growing surface and movement of
shadows means that plants in a greenhouse
receive a similar daily light integral. When
growing vertically, light intensity is decreased
by shelving or other structures, except for
plants growing at the top. In addition, plants
growing on the north side of structures
receive less light than those growing on the
other sides.
For commercial growers, a uniform and high
light environment creates uniform and highquality
plants. This means plants marketed or
harvested at the same time will have similar
growth characteristics. With many vertical
42 JUNE 2021 GPNMAG.COM
growing methods inside greenhouses, there
is usually more variability in light and thus
growth within a population of plants. This can
be mitigated to some extent by the use of
highly diffuse greenhouse coverings to scatter
the light inside.
Most commercial growers of greenhouse
vine crops use supplemental lighting. Lighting
fixtures placed above the crop means that
leaves lower in the canopy receive much less
light because of crop shading and the greater
distance from the lamps. Inter-canopy LED
lighting is the placement of fixtures between
crop rows in the lower part of the canopy. This
lighting strategy is possible when crops are
planted in rows, and may be less useful when
growing in vertical columns. Supplemental
lighting can be placed under shelves, but the
light intensity and spectrum are usually quite
different from plants on the top shelves that
are grown under sunlight.
Fertigation. Plants of a crop grown under a
similar light environment have similar needs
for water and fertilizer. When light is spatially
variable, plant size becomes variable, as does
the need for water and fertilizer. It is difficult
to manage a variable crop, although less
so when growing hydroponically. When not
using hydroponics, irrigation based on the
largest plants means the smallest plants will
be over-watered, and if based on the smallest
plants means the larger plants will receive
insufficient water.
Labor and automation. Vertical growing can
be challenging to manage with respect to labor
and automation. If growing towers are too
tall, plants can be out of reach, making crop
inspection and management more difficult.
There are some types of automated vertical
growing towers, but each one usually has its
own mechanical and watering systems that
need periodic maintenance.
While growing crops in vertical structures
is possible inside greenhouses, plants can
receive less and more variable light, which
results in more variable crop growth. Crop
management and supplemental lighting
can also be more of a challenge. Consider
whether any advantages of growing vertically
in a greenhouse are worth the production
challenges and constraints.
Figure 1. There are several
production challenges when
growing vertically inside
greenhouses.
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June 2021

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