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In my last post I talked about the importance of carbon dioxide in the greenhouse. I found a small portable propane heater I thought would interest small greenhouse owners. It is good for heating up to 250 square feet, and it vents inside, providing CO2 for your plants.

Good air circulation is very important in the greenhouse. It helps your plants “breathe” more effectively, and it reduces mildews and other diseases. Check out fans and other ventilation systems at Yardiac.com

Whether you heat your greenhouse or not, you willl want to take steps to keep your greenhouse from losing its warmth in the Winter. Of course, that is assuming you actually use your greenhouse in the Winter.

Stopping Air Leaks in Your Greenhouse

Just like in your home, the first step is to find and stop the air leaks.

• Weatherstrip doors and windows.
• Caulk around any seams or joints that are leaking air.
• Make sure automatic vent openers and louvers are well lubricated and working properly.
• If your greenhouse is not on a solid foundation, check around the bottom for air leaks and seal them.

Insulation

There are a variety of options for insulating your greenhouse. If you have any unglazed walls or portions of the roof, they should have been insulated when the greenhouse was built. Also the foundation and perhaps under the floor should already be insulated.

For the glazed portions of your greenhouse, you can use insulating curtains, removable insulated panels, or some form of temporary, extra glazing. Good quality insulating curtains, alone, can improve your heat savings by 58%. Aluminized vinyl or aluminized fabric make the best curtains. They do a good job of insulating, without being too bulky. Make sure that they seal well to the greenhouse so that cool air does not leak around the edges.

A sometimes  simpler, but less effective method is to add another layer of glazing. You can put plastic film up on the inside of your greenhouse, again, making sure it is well sealed. The only advantage here is that you do not have to keep moving it every day. If you have a small greenhouse, you could use plastic bubble packing material. That will do a much better job of insulating than a single layer of plastic film.

Rigid, movable, insulating panels are only a reasonable option if you live in a very cold climate. They are much more time consuming, plus you need space to store the panels when they are not in use. If you are planning to put in your own curtains or insulating panels, the book, Movable Insulation, by William K Langdon, is a must read. It is written for homes, but the ideas apply to greenhouses, and it is an complete resource on the subject.

Improve Thermal Storage

Whether you have a solar greenhouse or not, thermal storage is important in the Winter. In your freezer, if you keep it full, it lowers cooling costs. In the same way, keeping your greenhouse full, keeps it warmer. Adding containers of water or potted plants in any available space will make it easier to keep your greenhouse warm. Also, if you have a lot of unused space in you greenhouse, you could isolate it. Put up insulated walls in you greenhouse, to shrink the amount of space you need to keep warm. A good way to do that is to wall off the north side of the greenhouse. A lot of heat gets lost to the north side, if your greenhouse is glazed on that side.

Greenhouse Heating Systems

Heating under planting benches, or heating the soil directly, is much more efficient than heating the air in general. Apart from that, regular maintenance of your heating systems, to keep them working efficiently is the best way to reduce heating costs.

Well I was planning to buy a minimum/maximum thermometer, to keep track of the temperature in my greenhouse this Winter. They aren’t so easy to find any more. I finally found a circular style one and was about to buy it, when I decided to get something way cooler as well as more useful; my very own Wireless Forecast Station. It has a lot of useful and interesting functions. I call it Wilson the Weatherman, because there is a picture of a guy on it, dressed appropriately for the weather. Let’s hope he’s right! All this for under $40. Not much more than I was going to pay for a boring thermometer that wouldn’t even tell me what time the minimum temperature was.

Features

• Wireless sensor
• Indoor/Outdoor temperature
• Indoor humidity
• Atomic clock, with alarm and date
• Weatherman forecast icon, based on barometric pressure
• Minimum/Maximum Temperature for indoors and outdoors, with time and date stamp
• Minimum/Maximum humidity
• Optional extra wireless sensors. Can have up to three.
• Celcius or Farenheit

The list goes on. Now I can start reporting to you how my greenhouse is performing. It won’t be too interesting yet, as our overnight lows are still in the 50s. I just got the one wireless sensor. I will put the station in the greenhouse and the sensor outside. Hopefully the greenhouse won’t get below 14°F, because that is as low as it goes. The outside sensor goes down to -21.8°F. We never get anywhere near that cold.

It is even more important to manage you soil well in greenhouses than in the yard. Greenhouse soil tends to go “stale” much more quickly. I highly recommend organic gardening, for the health of the soil as well as the quality of your produce. And if you are not gardening organically, that raises the importance of soil management even more.

There are many nutrients in the soil that support the health of your plants, although many people still think in terms of N, P, and K (nitrogen, phosphorus, potassium). Besides the nutrients, there are countless organisms contributing to the health of your soil.

Whether you are using organic or inorganic fertilizers, yearly additions of compost, and/or manure to your soil will greatly improve its health. And once every few years, it is a good idea to remove three to four inches of soil and replace it, preferably with compost or compost mixed with rich, loamy soil or a commercial soil mix. Although the soil mix is basically inert, it will lighten up the soil in your beds, especially if they are completely contained. Fertilize regularly as you would in the garden. If your greenhouse beds are not right on the ground, you need to be careful of a build up of salts and minerals in your soil, especially with inorganic fertilizers. Make sure you water thoroughly, and you should change the soil more often.

Watering your greenhouse is different from watering your garden. The greenhouse maintains a higher humidity, but it is hotter and soil dries out more quickly. Monitor your watering closely until you understand your greenhouse’s rhythms. Make sure there is good air circulation, to avoid plant and soil diseases from the humid air.

If you have a greenhouse, you can garden anywhere. A small town in Canada’s far North has converted an old ice rink into a community greenhouse. They are really appreciating the fresh greens up there. And with 24 hours of sunlight a day in the Summer, things can grow pretty fast. See more at cityfarmer.org.

Greenhouse glazing, that’s the clear stuff that covers your greenhouse, comes in many different materials these days. When you are choosing your greenhouse kit or planning your greenhouse construction, you need to decide which glazing material will suit your needs.

The four most common glazing materials are:

• Glass
• Rigid Plastic
• Polyethylene Film
• Fiber Reinforced Panels (FRP)

Glass of course, is the traditional glazing material for greenhouses. It is not used as much any more. Mostly people designing and building their own greenhouse use glass, because they can find old windows for cheap or free. The advantages of glass are that it lets a lot of light through and it lasts a very long time, if it is not broken. Glass is also more environmentally friendly than plastic. The disadvantages are weight, fragility, and cost, unless you are a scrounger and don’t mind the look of a greenhouse made of old windows.

Rigid plastic is used almost exclusively in modern greenhouse kits. Plastic is light weight and relatively inexpensive. Acrylic does not degrade with UV light, but is does scratch easily and it expands and contracts, making installation more difficult. Polycarbonate is UV resistant but does lose effective transparency after ten to fifteen years. Double or triple walled polycarbonate retains heat very well and is very easy to install. It is the most common greenhouse glazing these days.

Polyethylene film is the cheapest and shortest lived glazing material. It typically lasts one or two years. In the long run it is not so cheap, especially if you buy greenhouse grade. Greenhouse grade works much better, but does not last much longer. Even the best film, in the best circumstances, only lasts three or four years.

FRP is another inexpensive glazing option. However the more expensive ones with UV resistance can last up to twenty years. One big advantage is that it diffuses light, so that it spreads evenly. Even though it diffuses light, it still lets a high percentage of the light through. Many people do not like the look of FRP, and it does not come in any greenhouse kit that I am aware of. However, if you are building your own, FRP is definitely worth considering.

My personal first choice for greenhouse glazing is glass, or a combination of glass walls and FRP roof. If I were buying a greenhouse kit I would get polycarbonate. If I lived in a cold climate, I would get triple walled polycarbonate, whether I was building my own greenhouse from plans or buying a greenhouse kit.