Beastly weather no problem when gardening in low tunnels
“Work leads to wealth.
Wretched poets, let us work on!
The caterpillar, by working incessantly,
becomes the rich butterfly.”
— English translation of “La Chenille” in Guillaume Apollinaire’s “Le Bestiaire,” 1911
French poet Guillaume Apollinaire (1880-1918) received a set of woodcut animals from his friend Picasso in 1906, and the gift inspired him to write 30 short poems in the style of a bestiary. This type of literature was popular in the Middle Ages as illustrated volumes in which descriptions of real and mythical creatures provided moral lessons.
La Chenille (The Caterpillar) teaches us that diligent work is richly rewarded, and this is certainly true when it comes to gardening in February and March. Low tunnels, which are called “chenilles” in France because they look like caterpillars, are useful for gardeners who want to reap the rewards of spring harvests by planting outdoors early.
Low tunnels will help protect our plants from freezing temperatures and frost during late winter and early spring. They are typically made by arching wire or PVC pipes about 18 inches high over a garden bed and covering the arches with floating row cover or plastic sheeting. Sometimes gardeners will skip the frame and use only floating row cover, so called because the lightweight fabric “floats” over the seedlings and rises as the plants grow.
Medium-weight floating row cover will protect plants from cold weather down to 25 degrees while allowing air, water and about 75 percent of sunlight through. Because the fabric allows some self-ventilation, I prefer floating row cover to plastic sheets. Another advantage of using crop covers is that they shield against insect pests (but also pollinators) and deter other nuisance critters like neighborhood cats.
Last year in Medford, the temperature in February dropped to 20 degrees during a few nights, so I doubled up the row cover for a bit of added protection. I’ve found the best way to attach row cover to a frame is by using clothespins or specially made row cover clamps available at garden supply stores. This allows for easier removal of the covers on warmer days. Gardeners who use row cover without a frame secure the fabric with rocks or U-shaped garden staples.
Setting up low tunnels in advance of sowing seeds will help to warm the soil to 50 to 60 degrees, the optimal temperature range for cool-season plants to germinate. The OSU Extension Service recommends direct sowing the following cool-season crops in February/March in the Rogue Valley: arugula, carrots, chard, chives, cilantro, collards, corn salad (mache), garden cress, fava beans, kale, kohlrabi, leeks, lettuce, mustard and turnip greens, bulb onions, parsley, peas, radishes, spinach and turnips.
Seedlings to transplant into the low tunnel during February/March include: asparagus roots, broccoli, cabbage, cauliflower, perennial herbs, lettuce, onion sets and strawberries.
Successful low-tunnel gardening in February and March requires controlling the interior air temperature. Cool-season crops grow best when the temperature doesn’t exceed 70 degrees inside the tunnel. Be sure to remove the cover when needed, keeping in mind that even with some air flow, temperatures inside the tunnel will be warmer than outside.
It’s a good idea to keep a thermometer inside the low tunnel. Eliot Coleman, author of the “Four-Season Harvest” (1999) recommends placing the thermometer in a white box with slats and place the box on the ground in the center of the tunnel. That way, the thermometer gives a more accurate reading of the ambient air temperature inside the tunnel, rather than measuring the direct effect of the sun’s rays.
Even though floating row cover allows moisture to penetrate the fabric, warmer temperatures inside the tunnel will increase evaporation. This means plants may need to be watered more often than outdoor plantings. Adequate water is particularly important during seed germination and the first two weeks of growth, as well as during head development of broccoli, cabbage, cauliflower and lettuce.
I’ve found the best way to test soil moisture is to poke an index finger about 2 inches into the soil within the root zone of the plant. If the soil feels dry, it’s time to water lightly. To prevent diseases and rot, be sure to water in the morning so the plants have time to dry out during the day. Coleman (1999) recommends hand watering plants in a low tunnel using a wand with that releases a gentle spray over the plants.
Low tunnels, or chenilles as the French call them, have much to offer gardeners during this time of year; however, leaf-chewing chenilles of the larvae kind have been cursed by gardeners ever since gardening began. Conversely, the bonnacon, a bull-like mythical creature featured in medieval bestiaries, would really be helpful. Supposedly, the bonnacon was able to spray flaming dung from its behind as far as 300 feet — what a boon for hot composting!
Rhonda Nowak is a Rogue Valley gardener, teacher and writer. Email her at Rnowak39@gmail.com. For more about gardening, visit her blog at http://blogs.esouthernoregon.com/theliterarygardener/.