A greenhouse is a big purchase that requires a great deal of thought and research in order to get it right the first time. Do you know what questions to ask about the biggest investment you’ll make in your garden? Well, we do—let us walk you through buying your first or next greenhouse so that you get exactly what you had hoped for in an indoor growing space.
Should I build or buy my greenhouse?
A simple greenhouse isn’t difficult to construct if you’ve got basic carpentry skills, but you can’t go about throwing up just any old greenhouse in any old spot. Before you attempt to build your first greenhouse, look at the kits that are available for purchase. In many cases, you may find that when you compare the materials lists, pre-fabricated structures offer a significant savings. You’ll also have the benefit of knowing that your greenhouse has been field tested by other growers and the bugs are already documented and worked out.
If, however, you need a specialized structure, or a custom-sized lean-to style greenhouse, the added expense of customizing your own greenhouse may be worth it. Still, look at other models to ensure that your greenhouse has all the right vents and doors in the right spots. It’s easier to build ventilation, irrigation and climate control into a structure at the design phase than after you’ve already broken ground.
How will the weather affect what I’m growing?
The best design, materials and equipment for your greenhouse will depend heavily on your local conditions. Windy or snowy areas need more structurally sound buildings with the ability to shed snow and allow winds to pass by without ripping the walls apart. Warm climates call for better ventilation: roll-up walls, shade cloths and mounting areas for additional fans are the name of the game. In cold climes, extra insulation and heaters will help you maintain a stable environment.
Heating and cooling equipment needs depend heavily on what you intend to grow and how violently your weather changes. If nights stay above freezing and you only use your greenhouse to start seeds, you may be able to get away without heat, but trying to grow tropicals in the North will demand an efficient heating system. Nearly everybody will need some type of cooling system because of the way greenhouses tend to amplify the rays of the sun, although many growers can get away with running fans and opening vents during the hottest parts of the day.
Shade cloths are handy if you’re growing plants with limited light tolerances or it gets more than a little warm in the greenhouse. Heat kills quickly, so this should be a serious consideration. If your vents can’t move enough air to cool your structure, shade cloths can help prevent some heat from entering the structure in the first place. Trying your hand at an extremely cool greenhouse in a very hot, humid climate is a huge challenge, but swamp coolers and air conditioners can bring the temperatures into range.
Does flooring make a difference?
Yes. And how—first of all, your greenhouse floor is most likely the largest heat sink in your structure, meaning that it will capture heat during the day and deal it out slowly as the ground cools at night. Depending on your needs and conditions, typical floors range from bare ground to gravel and even cement.
Cement floors are great for sanitation and keeping weeds from sprouting up unexpectedly in the greenhouse, but trap a lot of heat. If you struggle to keep your greenhouse cool, they’re not your best choice. They’re great, though, in areas where supplemental heating is necessary or where perennial weeds are a problem, because they both capture the most heat of any typical flooring and create a permanent barrier between your growing area and any weed seeds below.
Gravel is a pretty typical flooring material, and neither captures a significant amount of heat, nor does it return much at night. If you prepare your greenhouse site carefully and layer the ground with heavy geotextiles before laying a thick layer of gravel, you may be able to keep weeds down for a long time, too. Gravel floors often fail when growers are trying to cut costs and refuse to line them or only lay a thin layer of gravel on top of landscaping fabrics.
Bare dirt will work for a greenhouse floor, but isn’t recommended for a number of reasons, notably for its willingness to let any weed or grass seeds near the surface to germinate. Greenhouses often have ideal conditions for rapid weed growth, your greenhouse may be taken over before you know it. Many weeds carry diseases and attract pests, further complicating your greenhouse efforts.
What materials should I use for the structure?
Greenhouses structures come in a wide range of materials, from wood and plastic to aluminum and powder-coated steel—greenhouse coverings are no less diverse with glass and polycarbonates being common. Does it matter what you choose? If you plan to have your greenhouse around a while, it certainly does. Again, you should first limit yourself to materials that will handle your local conditions—don’t, for example, build a greenhouse out of PVC pipes if you know that your area regularly sees 12-inch snowfalls or high winds.
Most gardeners can’t go wrong with greenhouses made from powder-coated steel and covered in polycarbonate panels, but these structures can be costly and difficult to modify if you find you need more vents or want to add screens. Cedar structures are also long-lasting and are easier to modify than steel or aluminum, though they may attract insects as they age or retain spores over time. Aluminum is rot-proof, but very lightweight, so any structure designed with this metal in mind will need to be weighed down. PVC pipe should only be used for temporary hoop houses due to the material’s light weight and short life span.
Glass or polycarbonate are excellent choices for skinning hobby greenhouses, but great care must be taken with glass if you plan to mow or weed eat nearby. Polycarbonate can get a little foggy or yellowish over time, but if you hit one of these panels with a little piece of gravel while mowing, it’s not likely to shatter into a million tiny shards. Poly films and sheet plastics vary widely in their effectiveness over the long term—these thin plastics can become very brittle as they age and in windy areas, may tear frequently. When using film or sheet materials, thicker is always better.
What accessories does my greenhouse need?
The accessories your greenhouse needs will largely depend on outside factors, like your local conditions, the plants you intend to grow and how much time you have to devote to regular greenhouse chores. Automation isn’t necessary, but it can be helpful if you’ve got too many garden chores and not enough hours in the day. These are the most important things to consider when looking at accessories:
Fans – Vital to any operation where breezes can’t be counted on to move excess hot air out of greenhouses quickly—fans are easy to control and get the job done. They can also be used to help keep air circulating around plants with mold issues and toughen up little seedlings that will eventually be exposed to windy areas.
Heaters – Some areas need heaters more than others, but if you want to use your greenhouse all year, you’ll need one eventually. Various sizes are available, powered by gas, electricity, wood or solar—the size of heater you’ll need will depend on how much heat loss you anticipate on the coldest nights and the size of your greenhouse.
Vent openers – You can open your vents manually if you know you’ll be near the greenhouse all day throughout your growing season. If you don’t think you can make that kind of commitment to your greenhouse, automatic vent openers are the next best thing. Set them up to open when the greenhouse starts to build up heat and close when temperatures cool again.
Screens – They’re not always standard equipment for greenhouses, but they should be—after all, screens are your only hope for keeping bugs and various wind-borne seeds from finding their way in through your vents. The tighter the screen, the fewer things you’ll have inside, but you may need to expand ventilation openings to make up for the reduced air movement through the screen. Don’t forget to screen windows and doors while you’re at it. Read our page on screens for more>>
Anchoring systems – You can’t keep a good greenhouse down—well, not without an anchoring system, at least. Some growers use sandbags or cement blocks and they’ll work reasonably well, but if you’re installing an expensive greenhouse in a permanent location, give it a finished look with a proper anchoring system and rest assured that you won’t lose your building to high winds.
Climate monitoring equipment – From the most basic hygrometer and thermometer to highly advanced equipment that can turn fans and heaters on and off, there’s a climate control system just right for your building and budget. Many systems offer wireless displays that you can keep in a handy place indoors so you always know what your greenhouse is doing, even when you’re working on something else.
Irrigation systems – Irrigation systems can be as simple as a watering can or a hose, or highly complicated drip or mist systems on timers. A very small hobby greenhouse doesn’t need a lot, but larger greenhouses can be difficult to keep watered in the heat of the summer. Consider an individual system for each type of plant you’re growing so each plant gets watered exactly right. Some systems allow you to push nutrients through to plants as well.
Benches – Benches don’t seem like a big deal, but if you’ve ever been in a greenhouse that had poorly designed benches or none at all, you know they’re as important as the walls themselves. Select easy to clean benches made of aluminum or coated steel for best results, though wooden benches will work in a pinch if they’re thoroughly cleaned often and repainted or resealed yearly.