Organic University: Greenhouses for year-round food and farming
Part 4: Get growing
You've chosen your location, assembled your greenhouse, and fine-tuned your climate control skills—now it’s time to plant something!

By Katie Olender
May 12, 2005

Editor’s note: This is part four of a four-part series on greenhouse operation based on the author’s participation in a daylong Organic University workshop that was part of the Upper Midwest Organic Farming Conference, held in late February in LaCrosse, Wisconsin.

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: its crops!

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.

The number of quality harvests correlates to the soil quality and fertility, Biernbaum says; the better the soil, the more times you can harvest.
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 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,” Biernbaum says.

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 absorption.

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 multiple passes.

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 needed.

Now go. Pull out that seed catalog and start planning for next winter.
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. 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.