Pros and Cons
From this main difference can be inferred the advantages and disadvantages of each heating method. On one hand, the passive heating method is more eco-friendly and more cost-friendly in the sense that little to no electricity is required. However, it is very dependent on the strength of the sun's rays such that it is virtually useless during the winter months when the sun is at its weakest.
On the other hand, the active method requires electricity to operate, which can be costly, complicated and not exactly eco-friendly in general. However, you cannot discount the fact that it can be used during the hard winter months when the sun is nowhere to be seen.
Harnessing the Pros
Still, despite the above mentioned limitations, greenhouse gardeners use passive heating to improve plant growth especially during the summer. The trick is in harnessing as much solar power as possible, of which heat sinks can greatly help with.
Simply put, a heat sink is any kind of material that allows the heat absorbed during the day to "sink in". During the night when temperatures around the heat sink are cooler, the trapped heat is slowly released, thus, providing for more warmth. Ultimately, the plants are provided with heat despite the surrounding colder temperature.
Now, you might be asking exactly what types of materials make for good heat sinks. Well, just to make a few suggestions:
Concrete, blocks, paving slabs and rocks piled inside a metal cage
Plastic barrels with lids are filled with water to the brim. One side is painted black and the other side is painted white. The white side faces the plants in the greenhouse while the black side catches the rays of the sun during the daylight. Keep in mind that black retains heat while white reflects it, thus, the arrangement.
Compost and well-aged manure can be used to create hotbeds, which should also deter flies from coming into the greenhouse. Of course, there are garden tips to maximize the use of the greenhouse heat sinks!
1. First, you have to use non-reflective black and white paint on the barrels. This way, the maximum amounts of the sun's rays are absorbed into the heat sink.
2. Second, make sure that the heat sinks are facing the sides of the greenhouse where there is maximum sunshine. This often means the south-facing side although you have to observe your area to determine said site.
3. Third, the heat sinks must be located inside the greenhouse and slightly away from the sides. This is because the glass panes of the greenhouse can quickly absorb the heat being emitted by the heat sinks during the night, thus, negating their value for the plants.
4. Fourth, you can wrap the north side (or whichever side is receiving the least amount of sunshine) with bubble wrap. This way, more heat is retained inside the greenhouse. And it helps to ensure that the greenhouse is tightly sealed during the night, too.
With this information on passive heating, you should set to work and make Mother Nature proud!
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