Top 5 Things to Consider When Building (or Buying) a Greenhouse

TGN Interviews Sustainable Greenhouse Gurus Penn and Cord Parmenter

Nominees: Penn and Cord Parmenter

Home Digs: Westcliffe, CO

Companies: Smart Greenhouses LLC, Miss Penn’s Mountain Seeds

Website: Penn and Cord’s Garden

Follow At: Penn’s Blog

Fast Facts: If living off of a lush, year-round veggie garden is impossible at 8,120 feet in the wilds of the Colorado Rockies, please don’t tell Cord and Penn Parmenter. When this husband and wife duo first settled their 43 acres of “prime mountain real estate” in the early 1990s, neighbors (a.k.a. naysayers) said, “Don’t you know you can’t grow anything in the mountains?” A fledgling spring garden would soon fan the fire of protest that’s since sparked nearly an acre of bio-intensive and forest gardens, two hand-built, off-grid greenhouses, and seed-saving prowess that brings plants from around the world to the table. And that’s just on the Parmenter homestead. Away from home, Cord, a master blacksmith, now designs and constructs passive solar greenhouses for high country living; Penn helps set up seed libraries locally and sells wild mountain seeds worldwide; and the two teach classes at Denver Botanic Gardens on sustainable greenhouse design, mountain food gardening, seed starting … and life.

Nominated By: Cynthia N. | Cañon City, CO


Penn and Cord Parmenter -- Greenhouse

You describe greenhouses as the “star of the show” in high-altitude growing. Why do you consider them essential to success, and for which types of gardens do you most recommend them?

They are the stars of the show because our greenhouses are 100 percent sustainable—requiring absolutely no fuel at any elevation. A student of ours built one at 11,000 feet, and they grow food and medicine in it year-round with a very short sun window. And it heats their house! They’ve told us to recommend that people build one of our greenhouses instead of buying a solar array “because it feeds you too.”

For certain warm-weather fruits and vegetables, a greenhouse is a must at altitude. Cantaloupes, watermelons, long-season tomatoes, eggplants, etc.—they don’t like to drop 50 degrees overnight, and they need time. However, adapting seed to your environment is also most useful. For example, if you grow tomatoes sourced from other extreme climates and the seed is saved, the plants will improve very quickly to deal with the present conditions. I [Penn] grow many varieties of tomatoes in the OPEN at 8,000 feet. That is possible because I select short-season varieties from cold, high places, and I practice seed saving. Seed learns … seed remembers. It accumulates and carries the information into the next generation. Every season in Colorado is different—you can never count on what happened last year to happen again, so seed adaption is crucial. (I also grow a lot of seed in our greenhouses, as well as all of our starts.) The greenhouses allow us to grow anything we want at any time we want.

What are the top 5 factors to consider when purchasing or building a greenhouse?

  1. What kind of greenhouse do you want and need? What do you expect to get out of it? Season extension, production, hobby, year-round food production, etc.? Our greenhouses are balanced structures that work well year-round in many climates without the need for supplementary heating or cooling. The initial investment can be more than some options out there, but the advantage is that you won’t need any energy inputs to run them. Our structures work well in sizes of 1,000 square feet or less. (Greenhouses larger than 1,000 square feet tend to get more out of balance and may need some backup in certain climates.)Earth berm greenhouses or climate battery greenhouses can also be effective if properly designed and run. For cool-season crops in certain climates and altitudes, a hoop house can do amazing things as well, as Eliot Coleman has shown us. They can be great season extenders. But, at 8,100 feet in the Rockies, they are not effective in the winter. Additionally, if you have the resources to heat a plastic house, I suppose that there is a lot that can be done in them. The costs for winter production are very high, though, as are summer cooling costs.
  2. Survey your sun exposure. In colder climates, you will want to maximize your winter sun exposure. South to slightly southeast is optimal. In the summer, you may benefit from some shading. It’s important to know where the sun is coming from at different times of year. Where are the peaks and trees; what is blocking the sun? In addition, different types of greenhouses may require different orientations to be most effective. For the greenhouses we like and build, the sun comes in mostly from the south, while the north side is protected.
  3. Plan your placement. Will the greenhouse be convenient to access? Will it get good sun exposure? Will your building department allow you to build it, and what are the restrictions? What are the setbacks from property lines? What will your neighbors think and how will that affect you? A greenhouse can be made to work to some degree in just about any space. But it is important to consider the cost and whether it will perform to your requirements. A good location will make the greenhouse shine.
  4. Get a grip on glazing.* An all-glazed greenhouse is a booby-trap for the West. They have to be artificially cooled and heated in a 24-hour period here. They cannot hold in heat and are famous for freezing and over-heating. We create a balanced greenhouse—50 percent insulated, 50 percent double-glazed. We insulate anywhere the light is not optimal. We double the glazing no matter what materials we use, leaving an airspace in between. Critical measures to weigh in building your own are the water-to-glazing ratio (which is 2–5 gallons of water per 1 square foot of glazing) and insulation-to-glazing ratio (which depends on your position on the planet, with the “shadow line” crucial for a balanced design). The formula for the front angle of the glass equals your latitude plus 35 degrees.Setting a kit-built, all-glazed greenhouse on frozen ground will not grow food in winter in the West. Our greenhouses are permanent buildings on an insulated foundation, so the ground never freezes under them again. We grow directly into the earth inside our greenhouses—the plants know the difference! If you’re building your own, remember to insulate the foundation to the frost line for your latitude and longitude.*Glazing means anywhere the sun comes through—whether glass, greenhouse film, polycarbonate, fiberglass, etc. All-glazed means there’s no insulation at all. This include hoops, high tunnels, glass kits, all-fiberglass/pre-formed greenhouses, and all-polycarbonate greenhouses.
  5. Budget is always important. I recommend that people go as large as they can afford with our greenhouses (unless you just want or need something small). Remember, balance is important, and a larger greenhouse can be harder to balance, so there is a limit.

Do a lot of research and talk to different people who have experience in your climate. Perspectives can be very different. Also, marketing can be deceptive at times. You need to get a realistic idea of what the different types of greenhouse are good for—or not—as the case may be. Many times, we’ve seen people buy a kit greenhouse and then be unable to make it work. It ends up as a storage shed, because it turns out to be very effective at killing plants. It just doesn’t make sense to spend money on something that is not going to do what you want it to.

We have been growing year-round for more than 18 years in a greenhouse that cost us $150 out of pocket. I [Cord] designed that greenhouse after reading The Food and Heat Producing Solar Greenhouse by Bill Yanda and Rick Fisher. In a world of marketing, knowledge can be more powerful than money.

How do your “passive” solar greenhouses differ from “active” greenhouses? Why is fuel-free (or sustainable) growing possible in your area, while it may not be elsewhere?

Heat chases cold. Hot sun and cold nights make these greenhouses work particularly well in the mountains. The heat/cold exchange is at its best in these conditions. We use stored water, because it is four times more efficient than any other thermal mass. We only fill the barrels once, and they act as the batteries for the life of the building. All day the water absorbs the heat (cooling the greenhouse), and all night it releases it (heating the greenhouse). Long before you tap into all that heat energy, the sun comes up and it starts over again. If it never cooled off, these greenhouses might not work as well during those months. (If it’s 105 degrees in the day and 100 degrees at night, eventually the water would not be able to do its job as well.) We are using basic physics here, like using natural convection to move the air. Low vents and high vents in opposite and equal positions create natural ventilation, which is the key to plant health.

Even the vent openers are fuel-free. Their cylinders are filled with paraffin wax and, when it gets hot, the wax expands and the arm opens the vent. When it gets cold, it contracts and closes the vent. Since they are not made for year-round growing, Blacksmith Cord invented an adjustable attachment that makes the vent openers smarter.

What are the primary issues Cord helps clients weigh when deciding between purchasing or building a greenhouse?

Often, it’s a question of what you have more of: time or money. But there is more to it than that. If you design and build for yourself, you have the potential to get exactly what you want (assuming you have the necessary skills). Building it yourself can save you a lot of money in labor as well. A good set of plans will make the process go more smoothly. On the other hand, if you can find someone who has the skills to build you exactly what you want, that can be a blessing. Just be sure to find a contractor you can trust and who knows greenhouses or has a good plan to follow. Plus, each location is different in terms of bedrock, water tables, deep frost lines, etc. These all must be taken into consideration.

There are not a lot of options out there for purchasing sustainable, well-balanced greenhouses, but you can find information if you want to build or design one for yourself. We sell plans for our greenhouse designs on our website. We have had even novice builders produce good results with them. I [Cord] offer support to help with your success and am available to design, build, and consult on greenhouses. We also teach a design and building class at the Denver Botanic Gardens and at our homestead. I’m working toward putting together a kit to have available in the future as well.

You all are big fans of bio-intensive growing. Can you describe its basic principles and some examples, and let us know whether you practice it in your greenhouse, in your open gardens, or both?

Both! Bio-intensive growing is the work of John Jeavons and his book How to Grow More Vegetables. Bio-intensive is a method of growing that results in four times the traditional row-planted yield—using less space and water. In the West, water conservation is a constant. Double-dug soil preparation to 24 inches, equidistant spacing, composting, and mulching all help create beds Jeavons calls “living sponges.” They are lofted, hold water, and allow for intensive planting. Since we mulch, we hold in that moisture, while the evenly spaced plants create a living canopy, so we only weed once. It is highly efficient. We tested it ourselves the first time by planting two 100-square-foot beds with potatoes, one double-dug and one not. The double-dug bed yielded 150 pounds on the first try and the other one only 25 pounds. BOOM!

We do not row plant and never compress our beds by leaning or stepping on them. Instead, we build them so we can reach across from all sides to plant. We mulch very heavily with spoiled hay—8 inches or more. (We learned this from the old-timey The Ruth Stout No-Work Garden Book!) For fine seed, we mulch with our native piñon pine and juniper forest pine needles, just lightly until they are big enough to have heavy mulch. When we plant in seedlings, they get mulched right away, and we do not have to weed at all.

Soil structure needs to be left intact, so we do not flip or turn soil. The first 12 inches is removed, and then the next 12 inches (the subsoil) is loosened, and organic matter is added. Then, the topsoil is moved over on top of the subsoil without flipping it. This is basically a double-dig. You can watch it online or read about it from John Jeavons. Our family can double-dig a 100-square-foot bed in 30 minutes.

In a greenhouse, we plant a living, breathing ecosystem. I see people afraid to “plant too much.” In nature, the plants touch and mingle and interact. There is a canopy and an understory. Besides planting vegetables equidistantly in beds, we interplant everything—companion planting, crop rotation, lots of aromatics, flowers, exotics, and tropicals. We use one plant to help another. We also leave the door open so the ladybugs can fly in and lay their eggs, which are magically born right when the aphids appear on the kale. How do they know? It’s all connected in bio-intensive gardening—we feed the soil everything we take out of it and more!

Some would say that tomato production at 31 degrees below is simply impossible. Can you tell us why it’s not, share specific growing tips, and let us know some of your most loved tomato varieties?

Tomatoes are the Holy Grail of the mountains. They don’t want to ripen in cold temps, so mountain folk are famous for growing green tomatoes. Even though we grew small amounts of tomatoes (using high-altitude seed from the beginning) in the open, we knew it required a greenhouse to get the big loads. We also had no money, so we salvaged or built everything on our raw land. We gathered materials for a few years for the first greenhouse—and continue to salvage and re-use to this day. Since then, seed adaption has increased the outside tomato load significantly.

Our greenhouses are the most solid in the passive solar industry. We’ve gone into winter with 12-foot tomato plants fully loaded. At 20 to 25 degrees below, we have seen them continue to produce and recover well. We have had tomatoes survive 31 degrees below (or colder) and recover and start to produce again without extra protective cover or supplemental heat. If they had been young seedlings during that cold period, they would have just sat there and waited for it to be over. They wouldn’t have frozen, but they wouldn’t have been actively growing either. From mid-December to the end of January, all the plants slow down production due to lack of light. They pick up steam and start really producing again at the top of February. So, if the plants are already loaded, you don’t even notice that slowdown over the holidays.

Also, the sun almost always shines here—over 300 days of sun a year—and most days have some sun, so even when it’s cold, a little sun recovers the greenhouse quickly. A passive solar greenhouse requires you to plant it seasonally, so I would not have tomatoes up against the glazing in winter as it would be too cold, and I would not have lettuce up against the glazing in summer as it would be too hot. We change out crops regularly for plant health too.

Tomatoes with a story and high cold adaptation are my favorites. Sasha’s Altai has the best story and it is a 59-day, round, red, delicious, perfectly balanced tomato with an anti-hail feature as well! Sasha comes on very early. It is a small plant and sets its fruit very close to the stem, so when it hailed once and stripped the plants clean, the tomatoes were still okay close to the stem—amazing!

I find very obscure tomatoes from all over the world, and so many of those are my favorites for flavor, color, and shape. The Siberians are tomato specialists!  People like Brad Gates and Tom Wagner make my heart happy—they are our American rock star tomato breeders.

My longtime favorites grown in the open at altitude include Sasha’s Altai, Galina, Mt. Roma, Black From Tula, Grushovka, Wendy, Moscow, Early Siberian, and Crimson Sprinter.

Recommendations for flavor and beauty are Black Bear, Allegory Sunset, Green Doctors, Red Siberian, Olga’s Biggest, Noire Charbonneuse, Siberian Pink Honey, Dwarf Wild Fred, Tiger Eye, Pink Berkeley Tie-Dye, Malachite Box, Black Crimson, and Churra Plum (an Angora type!).

For the hot half of Colorado—”Down Below” (i.e., the Front Range)—these heat-tolerant tomatoes rule: Abu Rawan (Iraq), Rouge D’Irak, Rio Grande, Golden Grape, Tatar of Mongolistan, Afghan, and Basrawya (Iraq).

Are there specific plants that grow best in greenhouses? How about plants you should avoid growing in them?

Plants that spread by runners, like raspberries or mint, are not great in a greenhouse, especially a small one. (These can be grown in containers instead.) In general, if it can grow outside, do it! Grow things in the greenhouse that do not do well outside and that do not take up a lot of room. For example, you could grow winter squash in there, but it will take up a lot of space for a long time and you will have to hand-pollinate if you don’t let the critters fly in.

Tomatoes adore the greenhouse, as do basil, flowers (petunias are amazing in winter!), cucumbers, cantaloupes, all the nightshades, herbs, tender perennials, and any tropical plants, including fruits—we’ll be planting bananas, guavas, figs, oranges, and pomegranates soon. I [Penn] can also isolate seed varieties from cross-pollination by growing in a greenhouse (like corn, a wind-pollinated crop).

What resources do you recommend to those who want to learn more about building, buying, and growing in greenhouses? Can you share any specific greenhouse plans for those who’d like to build their own?

A smart greenhouse starts paying you back right away—you invest in a quality, no-fuel structure, and the return is amazing. We sell our plans here. We believe it’s the best deal in the business. And we’re just about to add another one, so there will be six sizes. The plans are thorough and highly detailed, with close-ups, supplemental material, and resources—yet still very affordable. If followed exactly, they guarantee a smart greenhouse, with all the kinks already worked out. If the builder changes the plans, though—say, by kicking it out a couple of feet—we can no longer guarantee the performance. One change results in a ripple effect, compromising the ventilation, shadow line, and overall balance. We reside in the sweet spot.

Here are resources we’d recommend:


(This article was originally published on December 5, 2018)


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