Food Protection Trends - January/February 2021 - 64

year (2%), four times per year (4%), and more than four
times per year (2%). In addition, 4% of growers tested
their growing media but did not know how often, and one
grower (1%) did not know whether their farm's growing
media was tested specifically for bacteria. Statistically
significant relationships were found between growing media
testing at least once per year and both the total number of
employees (P = 0.015) and the total number of employees
who directly handle the microgreens (P = 0.001). This
may indicate that larger microgreen operations are better
equipped to engage in routine quality assurance procedures
such as microbiological testing of media. Although the PSR
does not explicitly require microbiological soil testing, the
importance of environmental monitoring of food contact
surfaces (29) and data on differential survival of common
foodborne pathogens on soil-free growing media types (22,
65) indicate that the growing media is not without risk.
Testing of growing media is not only uncommon among
microgreen growers, but it appears not to be influenced
by any farm characteristics tested. Soil testing may not be
included in requirements for passing a GAP audit or included
in farm food safety trainings because it is not explicitly
required under the PSR. Furthermore, the only discussion
of growing media in the PSR is related to the proper use of
biological soil amendments of animal origin (57). Biological
soil amendments are used infrequently among microgreen
producers; among the small number who use them, worm
castings were mentioned most often. By contrast, two surveys
of field-grown produce farmers (1, 6) indicated that manure
use is quite common.
For questions about irrigation water testing, the only farm
characteristic that had a statistically significant relationship
with irrigation water testing at least once per year was
the type of production system (P = 0.01). The source of
irrigation water (e.g., municipal, groundwater, surface water,
rainwater, etc.) was hypothesized to be an influencing factor
but was not significant in our data (P = 0.49) because most
operations used either groundwater or a municipal water
source. Linear regression showed that " collected rainwater "
was a negative predictor of water testing (see Supplemental
Table S2). Overall, 48% of growers who responded to the
question test their irrigation water source at least once per
year. This proportion of growers who implement water
testing is similar to that reported in a 2018 national survey of
produce growers (1). Of those who answered the question
(n = 114), all aquaponics (n = 2) and hydroponics (n = 5)
practitioners in the survey reported testing their water more
than once per year. For growers who used the stacked tray
method, 18 tested their water once per year, 8 tested more
than once per year, and 5 did not perform water testing.
Among unstacked container growers, 6 tested once per year,
3 tested more than once per year, and 3 did not perform any
testing. Because the majority of responses for agricultural
water sources were either municipal or well water (61.9%),

Food Protection Trends January/February

the reported testing frequencies are in line with requirements
under the PSR (57).
For water treatment, 46.6% of respondents (n = 176)
did not perform user-side water treatment, and 35% did
not answer the question. The most popular type of water
treatment method among those who did treat their water
included activated charcoal filtration (6.2%), a sediment
filter (6.2%), and reverse osmosis (5.1%). Respondents were
allowed to choose more than one response for this question.
There were many unique combinations of water treatments
reported by respondents, but the most common combination
of water treatment methods was a sediment filter along with
an activated charcoal filter (n = 5).
Seed disinfection was also examined. Statistically significant
relationships existed between pregermination seed disinfection
and two farm characteristics: production system type (P = 0.001)
and total number of employees (P = 0.011). Interestingly, those
farms that did not disinfect their seeds prior to germination
had an average of 29 total employees, whereas farms that did
disinfect their seeds averaged 4 total employees. An in-depth
survey of 19 food safety experts and 32 produce growers (42)
also challenges the assumption that larger farms are more likely
to engage in more food safety practices than smaller farms. The
authors found that if a recommended food safety practice is
more challenging to implement on a larger scale, large farms
are less likely to do it. Seed disinfection may be a practice that
is difficult to scale. However, seed treatment for reduction of
microorganisms of public health significance is a requirement
for sprout producers, distributors, or suppliers under subpart
M of the PSR-an important distinction between microgreens
and sprouts (57).
By production system type, 40 stacked-tray growers (n
= 71) disinfected their seeds, 28 did not, and 2 did not
respond. For all other production system types combined
(n = 47), a greater proportion of growers did not disinfect
their seeds compared to those who did. In particular, 17 of
22 container farms reported not disinfecting seeds. This may
be indicative of the perception of less risk associated with
growing microgreens as compared to sprouts, which have
the requirement for seed treatment. Among growers of all
system types who reported having a seed disinfection step
(n = 46), 42 (91%) used a hydrogen peroxide soak. Sodium
hypochlorite (n = 3) and vinegar (n = 1) were also reported.
However, it is unknown whether the reported methods for
disinfection are based on scientifically valid methods because
concentration and contact time were not asked.
Harvest-related practices surveyed included harvest method, postharvest washing, and presale storage. Postharvest
washing was performed by 34 farms (19.3%) and was not
performed by 77 farms (43.8%), whereas 65 farms (36.9%)
did not respond to the question. The lack of postharvest
washing aligns with peer-reviewed research that reports a
negative effect on shelf life as indicated by final microbial
counts and damage to plant tissues, especially for the more

Food Protection Trends - January/February 2021

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