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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

Ironically, the greenhouse gas that everyone is worried about these days is usually deficient inside greenhouses. Plants require CO2 for photosynthesis, and in a closed environment, such as a greenhouse, they tend to use it up. For this reason it is important, especially in the Winter, to make sure you have adequate levels of CO2 in your greenhouse. In commercial greenhouses, CO2 levels are supplemented either with propane or natural gas heaters or with tanks of CO2. CO2 is a byproduct of combustion, so venting the heaters inside the greenhouse creates two advantages: heat and CO2. However water vapor is also a byproduct, so venting heaters inside will raise the humidity as well. Greenhouses are often overly humid already. That is why tanks of CO2 are used by many growers.

For the home greenhouse owner, it can be more difficult. A small greenhouse usually does not need a gas heater, and many people don’t want to use artificial heating. Setting a system using CO2 tanks is very expensive on such a small scale. One option is to bring air in from outside, using a heat exchanger to minimize heat loss. If you have the space, putting a compost bin inside your greenhouse can provide some CO2. Some people will use a CO2 type fire extinguisher, spraying it occasionally, inside the greenhouse. An advantage to having a greenhouse attached to your home is that you can open a window or door between them, providing warm air that is high in CO2. Another option for homesteaders with large greenhouses is to keep animals in them. The animals will breathe out enough CO2 to keep the plants happy. Having such an integrated greenhouse is tricky business though. Make sure you know what you are doing, so that the animals, as well as the plants stay healthy.

Another issue with CO2 in the greenhouse is that plants create micro-environments around themselves. If there is no air circulation, they will use up the CO2 close to their leaves and not get any more, even if there is enough in the greenhouse in general. That is one reason why fans are an important part of the greenhouse. Maintaining good air circulation in your greenhouse will improve the health of your plants in many ways.

If you have a well sealed greenhouse, it is imperative that you find a way to supllement the CO2. If you have a fairly leaky greenhouse, you can probably get away with improving the air circulation around the plants.

Well, it fell below freezing last night. Our overnight low was 30° F. My greenhouse did quite well considering, I haven’t caulked all the air leaks, yet. The low temperature in the greenhouse was 40°. The greenhouse has mostly single paned glazing. On the plus side I put about 140 gallons of water in there, which is almost one gallon per square foot of floor space. Considering I am in the Northwest, I think the greenhouse will perform just fine. I will be fixing the leaks and perhaps increasing the thermal storage, just to see how well it can do.

The main issue in our neck of the woods is getting enough light in the Winter months, so I will not decrease the glazing to increase the heat retention. Light seems to be good so far. We have plenty of Mustards and Swiss Chard growing like crazy.

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.

This is the kind of innovation I like to see. A greenhouse that is insulated by soap bubbles. This greenhouse is in the UK, but the original one is in Canada. Who said Canadians never invent anything? See more on the Canadian greenhouse here.

For small greenhouses, my favorite insulation on the south facing glazing is foil faced rigid insulation panels. You can design it so when they open up, they reflect more light into the greenhouse.

Related post: Solar Greenhouse Insulation

There are not as many good lean-to style greenhouse kits out there as I would like to see. I think building your greenhouse against another building is a great way to go, because of the insulation value of the other building. For some reason most lean-to greenhouse kits come with inadequate ventilation. Another problem is that most of them are small. I suppose not many people have a large space on the south side of their house to put a greenhouse. So, rather than a top 5, I have the top 3 lean-to greenhouse kits:

3. Sunshine Vertical Wall GardenHouse

This nice looking, small greenhouse kit has a redwood frame and polycarbonate glazing. It has a door at each end for excellent ventilation, but unfortunately, no automatic vents. If you want automatic vents, they suggest cutting the glazing and installing an opener. The kit is easy to assemble and it comes with an instructional video. For more information or to buy it now, click here.

2. Solexx Harvester Garden Greenhouse Kit

The Solexx greenhouse kits all come with revolutionary glazing panels, that provide optimal light for your plants. This greenhouse kit comes with shelving and rods for hanging plants. The only reason I do not make this number one, is that I feel it has inadequate ventilation. It has one door and one 12″ by 24″ vent. With increased ventilation, this can be a very nice greenhouse kit. For more information or to buy it now, click here.

1. Juliana Carport Lean-To Greenhouse

All Juliana greenhouse kits are of the highest quality, and this is no exception. It has plenty of ventilation, though automatic openers are sold separately. It has an easy to install, aluminum frame and double walled polycarbonate glazing. It comes with a twelve year warranty. Buy the Juliana Carport Lean-to greenhouse kit.

Juliana also has larger models in the lean-to style of greenhouse. To see them, click here.

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Top 5 Small Greenhouse Kits

Inexpensive Greenhouse Kits

Here is a list of what I consider to be the very best in small greenhouse kits available in the USA. When I say small I do not mean tiny. I am talking about 50 to 100 square feet. Great for the serious hobby gardener, who does not have a lot of space.

5. 6′ x 8′ Greenline Greenhouse

The Greenline greenhouse kit is made from aluminum and plastic, with strong, clear polycarbonate glazing. The glazing has 100% UV protection, giving the panels a long life. Very easy to assemble, if you are on flat ground. Comes with a free base kit, to anchor it to the ground. 5 year warranty. For more information or to buy now, click here.

4. 6′ x 12′ Sunshine Gardenhouse

This beautiful greenhouse is made with a redwood frame and double walled polycarbonate glazing. The glazing, which comes with a ten year warranty, is slightly diffused, making for happier plants. This greenhouse has automatic vents and plenty of air circulation. The redwood frame is made from only second growth wood and the base is made from recycled plastic. Buy the Sunshine Gardenhouse here.

3. 9′ x 10′ Juliana Premium Greenhouse

The Juliana premium greenhouse kit is very sturdy, and yet, easy to install and take down if you need to. It comes with thick, double walled polycarbonate glazing, to maintain the warmth inside. It has adjustable, automatic vents. This greenhouse kit comes with a twelve year warranty. For more information on the Juliana Premium greenhouse, or to buy now, click here.

2. 8′ x 10′ Riga Greenhouse

The Riga greenhouse kit is the most well insulated of the five greenhouse kits. It has 10 mm polycarbonate glazing on the front and back, and 8 mm everywhere else. The glazing comes with a ten year warranty and the frame with a fifteen year warranty. The unique shape of this greenhouse gives it strength and plenty of headroom. It comes with automatic vents and an extra large rear window. You can order it with or without shelves. Click here to buy the Riga Greenhouse kit.

1. 8′ x 8′ Solexx Greenhouse

I am a big fan of the solexx greenhouses. They are very strong, standing up to high winds and heavy snows. Although the double walled Solexx panels are thinner than most double walled polycarbonate panels, they have a high insulation value. The panels diffuse the light much better than polycarbonate does, creating ideal light for your plants. The frame is painted white to reflect the light onto the plants, as well. They come with build in benches at no extra charge. All this and they are less expensive than the Riga or Juliana Premium greenhouse kits. For more information about the Solexx greenhouse kit or to buy it now, click here.

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Top 3 Lean-to Greenhouse Kits

Inexpensive Greenhouse Kits