It is now the beginning of the end of my lecture-style introduction
to winter greenhouse production. Surrounded by other eager
farmers, I’ve learned about selecting a site and preparing
the soil, building a greenhouse, and managing its internal
environment. Pen in hand and
a fresh cup of coffee on the table in front of me, I am finally
ready to learn about the most important part of the greenhouse:
I am excited to be here at Organic University, the prequel
to the Upper Midwest Organic Farming Conference in LaCrosse,
Wisconsin and even more excited to be seated in John Biernbaum’s
lecture. If there is one person who knows winter greenhouse
production, it is Biernbaum, who is a professor of horticulture
at Michigan State University and a faculty advisor to the
school’s Student Organic Farm.
Biernbaum begins the final section of his lecture by discussing
what should be planted to have a bountiful winter harvest. First,
he recommends baby salad greens for several reasons. The smaller,
less-mature leaves are cold tolerant, an important quality when
considering Midwest crops in wintertime. Baby salad greens are
a high-value product that receives much positive attention in
winter, especially if you combine different varieties so the
final salad mix is of multiple colors and flavors. Finally,
baby salad greens give good economic returns per unit area because
they can be harvested multiple times.
||The number of quality harvests correlates
to the soil quality and fertility, Biernbaum says; the
better the soil, the more times you can harvest.
“The planting density of your baby greens will have
a significant impact on yield, quality, and sometimes leaf
size,” Biernbaum says. Follow the recommendations of
your seed catalog when choosing seed planting density, he
advises, adding that you may adjust the density down the road
based on your own experience. The Student Organic Farm uses
a four-row pinpoint seeder. Student farmers there began with
recommended settings from Johnny's Selected Seeds but soon
devised their own table to better reflect their specific growing
conditions and results.
Most baby salad greens are harvestable when just 3- to 4-inches
tall. Mustard and Mizuna, the main exceptions, are harvestable
at 2- and 5-inches tall, respectively. Cut approximately one
inch above the soil, Biernbaum instructs, and be sure not
to cut the growing point.
While baby salad greens can be harvested multiple times,
he says, flavor and quality may change in the later harvests,
particularly with arugula and ‘Red Giant’ mustard.
Although some growers of baby salad mixes marketing to high-end
restaurants replant the entire crop after the second harvest,
Biernbaum says, the Student Organic Farm serves mostly CSA
customers and so stretches the number of harvests to as long
as each crop holds up and remains palatable.
After baby leaf salad
greens, Biernbaum recommends growing leafy vegetables
like spinach, chard and beet greens in winter.
‘Bulls Blood’ beet, ‘Tokyo Bekena’
Chinese cabbage, several varieties of lettuce, ‘Red
Giant’ mustard, sorrel and tatsoi are harvested two
to three times. Claytonia, kale and ‘Green Spray’
mibuna are harvested three to five times before replanting.
The number of quality harvests correlates to the soil quality
and fertility, Biernbaum says; the better the soil, the more
times you can harvest.
Before moving on to the next winter crop type, Biernbaum
shares his experience regarding specific salad greens. Mache
(a.k.a. corn salad) is very hardy in cold temperatures, he
offers; it does, however, have a slower growth rate so is
usually only harvested once or twice before it needs to be
replanted. Kale has been a consistently reliable crop for
the Student Organic Farm, Biernbaum says—it offers a
ruffled leaf to add volume—though little weight—to
your salad mix. Claytonia is an excellent cold-weather performer
that adds weight, he says, though it is slow to get started.
Biernbaum warns that the best way to avoid disease—such
as fuzzy growth on leaves, brown or rotting foliage, or spots—is
to not plant too densely and to use good water practices.
Good water practices include watering less often in cool weather
(because the water does not get absorbed or evaporate as quickly
as in warm weather) and watering close to the ground to avoid
drenching the foliage.
After baby leaf salad greens, Biernbaum recommends
growing leafy vegetables like spinach, chard and beet greens
in winter. All of these crops are direct seeded and covered
with screened compost.
Asian greens, like Chinese cabbage, boc choi, mequing choi
and tatsoi, are a good choice for your third crop type, he
says. These are all seeded in flats about a month before planting
them in the greenhouse. The transplants should be planted
at the end of September or early October, Biernbaum say, and
should be placed about 12 inches apart in each row with 12
inches between rows.
Finally, Biernbaum recommends root vegetables as a fourth
crop. The radishes, beets, turnips, carrots and other root
vegetables grown at the Student Organic Farm are direct seeded.
Carrots have to be seeded by the first week of August, he
says; radishes, turnips and beets can be seeded in September.
“Our biggest problem with these crops is the four leggeds
that help themselves to a bite out of the tasty above-ground
roots,” Biernbaum says.
Biernbaum reminds us that with biennial leafy and root vegetables,
spring bolting (flower stalk formation) is to be expected
if overwintered crops are still around in March and April
when temperature and daylength both increase. Bolting ruins
root crops, he says, so they need to be harvested well before
they bolt. “We have actually found that our CSA members
are happy to have spring leafy or Asian vegetables, even if
bolting has started,” Biernbaum says.
Last but certainly not least, Biernbaum provides some pointers
about proper watering techniques. First and foremost, he says,
is determining when to water. And the first step in this process,
Biernbaum says, is to check the weather when deciding whether
to water on a particular day. Then, he says, check your plants,
the soil surface and the soil moisture several inches below
the surface (you can just dig your finger in the soil for this
part.) Third, check the thermometer to determine the air temperature
inside your high tunnel or greenhouse.
“If the sun is shining or is going to shine, and it
likely will reach 60 degrees Fahrenheit or higher in the greenhouse,
and the soil is not already wet, water!” Biernbaum says.
He recommends watering before 11 o’clock in the morning
but no later than two o’clock in the afternoon to allow
plenty of time for foliage to dry. When it is cool, he says,
do not water, because the leaves and the area immediately
around the plants do not dry well, creating a hospitable environment
for foliar pathogens. When it is cloudy in the winter, Biernbaum
says, the plants do not grow much and so need less water.
Again, he reiterates, do not water on cold, cloudy days. “Ideally,
we want the plant leaves to be dry and the top of the soil
not to be wet going into the night with freezing conditions,”
I had no idea how
much you had to consider before watering!
Next, he explains how much to water. This varies among greenhouses
because soil type and organic matter impact the rate of water
I had no idea how much you had to consider before watering!
But finally, just as I am starting to worry we will
never actually learn how to water, Biernbaum launches into
just that. If you use a hose and breaker by hand, he says,
make sure the breaker head is free of solid matter. Biernbaum
recommends a quarter-turn valve on the hose end so you can
easily and quickly turn the water on and off. Keep the breaker
moving, he says, to avoid compacting the soil. The flow rate
should either be high with the water shooting away from you
and falling on the soil at a distance, Biernbaum says, or
low with the breaker held near the soil to keep water off
the foliage. Avoid creating puddles, he says, which may require
Finally, he says, drain the hose or water line after each
watering to prevent freezing, remove the breaker and quarter
valve, and pay attention to where the water drains to avoid
a puddle in the aisle.
It sounds like a lot to plan between choosing the right plants
and watering effectively, but Biernbaum tells us we will all
learn what works best for us with our own specific crops and
conditions over time. “Learn from experience,”
he says. “Keep records, including the spacing you used
for your seeds and the watering information.” This way,
Biernbaum says, you can go back and adjust your methods as
Closing his lecture, Biernbaum reminds us of what he tells students
to remember while giving tours of the winter greenhouses. “There
are four key things that make it work,” Biernbaum says.
Holding up fingers as he counts, he says “The right plants
(cold tolerant), planted at the right time (before the days
get too short and temperatures too low), using multiple harvest
or cut-and-come-again harvesting, and crop protection from wind
and excess moisture. It is all about understanding the system
to allow local food all winter long.” Thanks to Biernbaum’s
presentation at Organic University, a whole crop of Midwestern
farmers now have the basis of that knowledge.
||Now go. Pull out that seed catalog
and start planning for next winter.
Now go. Pull
out that seed catalog and start planning for next winter.
And invite your buddies who helped build the greenhouse over
for a potluck with all the fruits (or shall I say vegetables)
of your labor.
Katie Olender is a senior majoring in agricultural communications
at Michigan State University.