Hoophouse Gardening: Getting a big jump on spring

Blustery though it has been recently, we are on the brink of planting many of our seedlings - loads of different lettuces, pak choi, kale, chard, onions, spinach, brussel sprouts, cabbage. Crazy? For sure. But not about gardening in March. We are in the enviable position of extending Michigan’s growing season by transplanting our cold-crop seedlings in our year-old 26′ by 36′ passive solar greenhouse called a hoophouse. The sunshine available even on a cloudy day is enough to warm the hoophouse 10 to 20 degrees above the outside temperature. The temperature inside the hoophouse does plunge at night when the sun goes down, but even if the hardened plants freeze, they will thaw out the following day and resume growing. We spray painted some empty milk jugs black, and in the spring, we will them with water. They absorb sunlight during the day and radiate back some additional heat at night.

One thing I have learned is that it takes careful planning to produce the succession of cold and warm vegetable seedlings required to keep the hoophouse as productive as it can be through the extended spring-summer-fall growing season. Right now, I have four tiers of cold veggies under lights, with additional warm crop veggies such as tomatoes and peppers under lights in the basement. Some veggies can be direct-seeded into the hoophouse far earlier than they would in a regular garden. I rely on the handout provided by Michigan State University hoophouse specialist Adam Montri for guidance. But I must say that it seems strange to raise seedlings indoors during the summer in preparation for late-season plantings. Michigan is at the forefront of experimentation with this remarkable new way to produce food all year round without supplemental heat.

We bought the hoophouse to maximize our ability to raise our own food, and we were able to harvest lettuces and other greens all winter. In addition to helping us overcome the limitations of Michigan’s relatively short growing season, it also keeps the deer and bunnies from wiping us out, as they did so often in the past.

Total costs for our unit and additional supplies was about $2,500. Many thanks to the friends who helped us put it in. We expect to replace the plastic in five or six years, at a cost of about $500. (That fee may double if we elect to make ours a double-walled unit inflated with a small solar-powered fan.)

More sophisticated units have automated roll-up sides, since the challenge in the summer is to keep the interior cool enough. I simply roll up the sides with the hand-crank that was provided, but that means you have to be available to put the sides up and down as needed, often on short notice. During July and August, the interior of the hoophouse can quickly go above 100 degrees if you leave the sides rolled down.

Challenging as well is keeping the plants watered. I always find it odd to be out there watering even after a thunderstorm has gone through. But part of why plants thrive in a hoophouse is that they are protected from punishing winds and downpours.

Some people run a special line to the hoophouse with a frost-free hydrant to water during the winter. However, Adam Montri has found that the moisture inside the hoophouse is sufficient to keep the plants healthy until spring when it is again possible use hoses without fear of freezing./

This will be our first full year with the new unit in place, so expect frequent updates. Our new freezer is ready and waiting to help us make the most of our anticipated hoophouse bounty.