by Sanne Kure-Jensen
Paul Arnold and his wife continuously seek equipment and growing techniques that minimize work and maximize profits. In the past eight years, the Arnolds have built three large high tunnels. Their tunnels are 30 or 34 feet wide and 144 feet long. They recommend a minimum width of 30 feet for winter growing in the colder zones. Their tunnels were constructed with automatic roll-up sides, water and electricity. The Arnolds use “sun-driven” growing without supplemental heat. Soil beds are prepared and balanced with compost and organic nutrient amendments as needed according to soil tests.
The Arnolds invested $20,000 to $30,000 for each high tunnel and achieved short paybacks of under two years. The farmers’ high production/low labor plan works because the Arnolds pay attention to details and train their workers to be efficient. They are great marketers and they balance their production with growing demand at two weekly winter farmers markets.
The Arnolds routinely try new varieties and keep careful records of their results. They track the progress and yields of each trial planting according to growth, disease resistance, color, yield, etc. They collect weather data both outside and inside their high tunnels using data loggers. Arnold reminded his audience that each farm and planting date would yield different results based on weather, sunlight, temperature and soil nutrients.
The Arnolds seed all lettuce varieties separately for easier harvesting and quality control. After their first winter trial (2012-13), they are pleased with the one-cut Salanova lettuce for winter production. It was very cold-resistant and had no disease issues in their trials.
Starting some winter greens as transplants allows summer produce like tomatoes to grow later into the fall inside high tunnels. The Arnolds use successive weekly plantings for most of crops, to minimize risks from variable fall weather.
At Pleasant Valley Farm’s zone 4 site, Asian greens are seeded in the greenhouse from Sept. 1 to Sept. 15. Spinaches are seeded from Sept. 20 to Oct. 1. Direct seeding is done between Sept. 20 and Oct. 10 for lettuces/salad mixes, mustard greens and spinach. Arugula is direct seeded successively between Oct. 1 and Dec. 1. Beds for transplants are prepared in late October and the greenhouse transplants go in between Oct. 15 and Nov. 1. Salanova lettuces are seeded weekly in the greenhouse starting in later August and transplanted into the tunnels on a 6” by 6” pattern.
In early January, Asian greens, lettuces, mustards and salad mix greens are seeded in 72- or 128-cell trays inside the greenhouse. They are transplanted into high tunnels in March where other crops have finished. This allows for a continuous harvest in April and May.
Each tunnel has either six or seven raised beds, approximately 3’ 6” wide, that are formed by hand. Three rows of kale or Swiss chard are transplanted per bed alternating French Intensive-style with two rows of Asian greens. Spacing is 8” x 12” for kale, Swiss shard, Asian Greens and Happy Rich Broccoli. Spacing is 5” x 8” for spinach transplants and 8” between rows when spinach is direct seeded. Arugula, lettuces for salad mix and mustards are direct-seeded at 2.5” spacing between rows.
These planting dates generally yield a harvest starting in December. Most crops are ready in January after the last outdoor plantings are sold. Growth is slow in December and January. As days lengthen in February, growth and re-growth rates accelerate. Multiple cuts continue through the end of May. The three tunnels average 125-175 pounds of greens weekly. Winter averages are over $1,700 gross per week.
Arnold stressed the need to keep leaf surfaces dry and high tunnels below 85 percent humidity. Large end vents are open 24/7 and HAF fans run daily to circulate air and minimize diseases. Regular scouting for pests and diseases is important to catch any issues early. Arnold utilizes soil drenches to prevent soil-borne disease outbreaks. Transplants are drenched in the greenhouse prior to transplanting. The drenches may be repeated after 6-8 weeks, if necessary. Aphids are the only major insect pest. Ladybugs are purchased in February or March to control them.
Drip tape and overhead watering are utilized all winter. Occasionally, hand watering may be needed. Overhead nozzles should be self-draining, so they will not freeze in the winter. Arnold recommends regular weeding to reduce competition for nutrients, light and water.
Arnold likes to keep the row covers off as much as possible to maximize light. He will use one, two or three layers of P30, depending on nighttime temperatures. Row covers are removed daily when it is warm enough and put back by mid-afternoon/evening when temperatures will be below 32 at night. “Row covers must remain dry,” said Arnold. Low row covers can rest on very low hoops or directly on crops to keep nighttime temperatures warmer. Farm experiments showed that using black plastic mulch as a weed barrier also kept soils warmer and led to increased growth.
Profitable winter greens production in unheated high tunnels
by Sanne Kure-Jensen