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5 Things to Consider Before You Buy a Greenhouse

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As our climate changes, a greenhouse brings stable growing conditions for gardeners.

By Eartheasy Posted Feb 19, 2015

Greenhouse
Whether you’re a new gardener or a seasoned grower, you’ll find some compelling reasons to invest in a good greenhouse. Flexibility: a greenhouse allows us to grow a wider variety of food and flowers, and to experiment with crops we previously considered “too delicate”. Stability: a greenhouse offers a predictable environment which shelters tender plants from damaging weather extremes. Self-sufficiency: a greenhouse empowers us to easily save and germinate our own seeds, making it possible to avoid paying for commercial starters.

And like it or not, the global climate crisis is coming home to our gardening landscape. With no shortage of record-breaking snowfalls, “never before recorded” temperature trends, and much of the country still threatened by drought, the only thing we can count on, weather-wise, is unpredictability. Climate change is here, and the first ripples are touching every aspect of our lives — especially in the garden. Freak weather systems can break plants, wash away your hard-earned soil, and encourage new pests. Changing times call for changing methods: the greenhouse gives your growing things shelter from the storm.

With so many greenhouse kits on the market, in such a variety of sizes, shapes, materials, and prices, it’s easy to get confused. Here are the basic questions you need to consider in choosing a greenhouse which best suits your gardening needs.

growing vegetables

1. Sizing: do you need a Starter or a Grower Greenhouse?

What’s your vision? Maybe you love to garden outdoors but are tired of the lack of variety and high price of buying seedlings. You’re just dreaming of starting your own seeds from scratch indoors, giving them a warm environment and a strong start before your local spring is in full swing. If so, a relatively small “starter” greenhouse may be quite adequate for your needs. Just add a potting bench, soil, and a handful of seeds: you’re ready to go.

Or perhaps you’re ready to kick your garden production into high gear. You might contemplate a greenhouse as the fundamental growing tool, with room for plants to expand to their full size and bear fruit under carefully managed ideal conditions. This will require a “grower” setup, with more room (how much is up to you) and different glazing (see below). Or maybe there are crops you’ve always wanted to try which simply won’t tolerate your climate — would you like to grow citrus trees in the northwest? Or rows of fresh, living greens in the dead of winter (elevated planters are ideal for this purpose)? With a little planning, you could stock your own booth at the local farmer’s market with a variety of greenhouse-grown veggies, ripe and ready to pick months before their outdoor-grown counterparts. If so, plan accordingly. There are greenhouse kits to suit every need.

Cold frames are the smallest “greenhouse” — these simple boxes are easy to move from one garden bed to another to protect young plants while there is still danger of frost. You can even make your own portable cloche as an introduction to the benefits of a controlled environment (of course many gardeners continue to use their cloches and cold-frames in addition to a large greenhouse. These small accessories require no foundation or building permits — but both their capacity and their versatility are limited.

How big is big enough? Walk-in options range from the compact “Lit’l Propagator” with just a 4’x4’ footprint, to the capacious 20’x16’ “Conservatory”, large enough to accommodate a commercial operation. Conventional wisdom holds that you should always buy the largest greenhouse your site and budget will allow. If you opt for the smaller of two possibilities, you are likely to wish for more space soon. If you currently have an outdoor garden, it’s worth asking yourself: did my garden beds begin this size, or have they expanded over the seasons? Most of us find ourselves widening the boundaries a little bit every year. A greenhouse is harder to enlarge, but our love for gardening has a tendency to grow and become more ambitious with time.

Assembling greenhouse

2. Glazing choices: should the panels be opaque or clear?

You’ll find three distinct choices for greenhouse panels: clear, diffused (or opaque), and semi-diffused. These options determine the strength of the light your plants will receive.

If your primary goal is starting seedlings for transplanting outdoors, the direct light of clear panels favors seed sprouting. Your starts will pop up more quickly and get a strong, energetic beginning in life. Glass panels and single-walled polycarbonate are clear and provide no diffusion. Snap & Grow makes an easy-to-assemble clear polycarbonate greenhouse, available in your choice of length.

For growing plants to maturity, however, diffused light is actually better. With a diffused cover, like the many options from Solexx, plants achieve optimum photosynthesis and tend to develop better shape: more balanced and compact, rather than tall and leggy from reaching toward direct light. Multi-walled polycarbonate and twin-walled polyethylene both provide good diffused light.

As you might guess, the semi-diffused cover is a compromise, often used for a dual-purpose greenhouse. The light will be somewhere in between. RIGA makes several all-season semi-diffused houses. Another fusion option is a diffused roof with clear sides: this design will allow more light in when the sun is lower in the sky, as it is in the spring and fall in northern climates.

greenhouse in winter

3. Insulation and design: how’s the winter weather?

If you live in a climate where ice and snow are part of your typical winter scene, and you want to grow vegetables year round, your cover needs to be well-insulated. Multiple-walled polycarbonate is often used for this purpose: the internal air spaces between the layers (either double or triple) provide significant insulating value. Twin-walled polyethylene is another great option which provides a soft, diffused light, and excellent insulation with more flexibility than rigid polycarbonate. The Solexx line of greenhouses uses twin-walled polyethylene in a wide variety of sizes and shapes. Another consideration in cold climates is snow accumulation: check the snow-load rating for the model you’re considering to make sure it won’t risk collapse after a heavy snowstorm.

If, on the other hand, your winters are mild, or if you are simply looking for a “season extender” (a place to germinate and nurture young plants in early spring when outdoor temperatures are still uncertain), serious insulation is not as crucial. Simple tempered glass panels or single-walled polycarbonate may be perfectly adequate. Glass won’t degrade under years of intense sunlight, but glass’s fragility makes it a poor choice for areas with hail storms, or heavy winds causing flying branches or ice. Polyethelene film is commonly used as a cheap-and-easy method, providing semi-diffused light — the downside, however, is the film’s short lifespan and lack of durability. Any heavy weather or falling branches can easily damage or tear the film, and the material photodegrades quickly. It may seem economical at first glance, but you’ll need to factor in the cost and trouble of frequent (between 1-6 years) film replacements. And even for a season-extender, insulation will still improve the performance.

If you live in a windy area, standard polyethylene film will not be a workable option, but the tougher woven polyethylene could still work. A more substantial material, such as twin-walled polyethylene or polycarbonate, on a rigid frame, will perform better in the wind. To prepare for potential gales, pay extra attention to anchoring your structure to the ground, and always ensure all doors and windows are closed before a storm hits.

If you’re thinking of a glass greenhouse in a cold area, consider using glass with a heat-retaining coating, such as “low-E”, particularly on the north side of the building (it will reduce the solar gain if used on the south faces). Will you be heating your greenhouse? If so, an insulated material is essential, to avoid wasting money and fuel on heat which flies through your windows almost as fast as your heater can produce it. Twin-walled polyethylene has the highest insulating value of any greenhouse glazing.

Plants in greenhouse

4. Logistics and landscape: your site, your zoning, your neighborhood.

Choose and mark the site where your greenhouse will go. String and pieces of rebar can be used to approximate the size and shape you’re planning on. Spend some time visualizing how this will impact your outdoor activities and your sight-lines, as well as your neighbors’ views. A greenhouse can be a thing of beauty — choose one which appeals to your aesthetic sense, and leave room to create whatever landscaping features you like around the edges. Again, note local weather considerations: for example, use another structure or a row of trees for a wind-break against the prevailing wind direction, if you can do so without losing too much sun exposure. Consider the sun exposure in all relevant seasons.

Before making your choice, make sure to check your local zoning regulations. Some neighborhoods or planned developments require asking permission before installing a greenhouse, and other areas may have restrictions on the size or setback requirements. In some cases, a smaller greenhouse could be subject to fewer regulations, if it qualifies for a different category of outbuilding such as a “storage shed”.
watering plants in greenhouse
Any greenhouse which attaches to your house (often called a “lean-to”) can be considered an addition and will likely require more permitting and restrictions. In addition, any attached greenhouse is likely to cause excessive-moisture problems in the home.
Check the recommendations for site-preparation before purchase, to ensure you’re ready to meet the requirements: leveling the footprint and providing a good drainage material are crucial for the long-term stability of your greenhouse, but concrete slabs are rarely necessary. Most greenhouses are sold as kits requiring assembly: prepare to get to know your greenhouse panel by panel, from the ground up. Two installers are needed for most kits. If you don’t have much building experience but are interested in trying, ask as many questions as you can about the tools and skills required. Reputable manufacturers have user-friendly instructions and good technical support. After a weekend of greenhouse-building-immersion, you’ll walk away proud of your part in this beautiful, useful structure.

5. Reputation and service: know who made your greenhouse.

A greenhouse — even a small one — costs real money and involves time and effort to set it up. Do yourself a favor by reading up on the company which makes and sells the greenhouse in advance, or ask the opinion of someone you trust who has done their research. Read the fine print and satisfy some basic questions:

  • What kind of warranty is provided? How many years, and what types of issues are covered?
  • How long has the company been in business, and how many kits has it sold? With such a significant purchase, many want to go with a known seller and manufacturer with proven track records. A long warranty may be no good if the company folds next year.
  • How is the greenhouse shipped and packaged, and what will the shipping cost? Always check everything for shipping damage before you begin construction.
  • What kind of technical assistance will be available, for pre-purchase questions, for help during set-up, or for later troubleshooting? Are representatives available on weekends for installation questions?
  • Where are the products manufactured, and do customer service representatives have direct experience with the products?

Gardening clubs or online garden forums are both useful places to ask around. Many experienced growers have seen several different models in action over the years, and may be able to offer insight into the performance of a particular model both out of the box and as it ages.

Get ready to expand your notions of what, when, and how much you can grow at home. It’s a revelation to be able to produce, in our own backyards, many favorite fruits and vegetables previously bought at the market! In many cases, a greenhouse is the crucial structure required to complete the full circle of gardening, seed to harvest.

No matter where we live, we can’t count on upcoming growing seasons mirroring the summers of our childhood, or even last year. More than ever, we’re at the mercy of climate forces beyond our power. In hopes of regaining some control over the harvest, many gardeners are turning to greenhouses. Though the outside temperatures may fluctuate wildly, the hail may fall and the wind may blow, inside the greenhouse the air is calm and stable.

For more details on greenhouse materials, construction, accessories, and use, read our complete guide to choosing the right greenhouse. Happy growing!

Posted in Organic Garden Tags , , , ,
  • I had no idea there was so much to consider in planning whether and how to set up a greenhouse.

  • Parth Patel

    Nice ideas for purchasing new greenhouse.
    really nice

    • Thanks Parth, your comments are appreciated.

  • Glenn Howard

    many good designs online,, 10×12 is great for small family, store garden plants and stuff in winter. work in it when raining, single wall doesnt cost much- but greenhouse plastic ours lasting 4 years ! only 50 $ its a hoop so wind doesnt damage if placed right.

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