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Working and building the domes has been exciting, but also very beneficial. We traveled around St. Louis teaching kids and adults about the purpose and functions of the greenhouses. Also, we supervised the building of domes at different community centers. With a geodesic dome greenhouse, you can extend the growing season of your plants and protect them from the harsh weather outside.
Greenhouses and how they work:
Here's what we learned about why our dome (and other greenhouses) help plants live for a longer season:
Plants germinate (sprout) from seeds and grow through their life cycle depending on light and soil temperature. We couldn't do much about how much the sun was shining, but our dome made the air, and the soil in the dome warmer than outside the dome. From what we saw, it seems that growing season depends more on soil temperature than light, because some of our tougher plants like cabbage and lettuce kept growing in our dome most of the winter. They slowed down a lot, though.
But we wanted to know, why is it so hot inside??? We can tell a difference when we step inside right away, even though the plastic is not that thick. It's much warmer and the air feels sticky sometimes. It feels really nasty in there sometimes in the summer. There are 2 main things that our dome does to help the temperature stay warmer than the outside air.
1. The air inside the dome is separated from the air outside of the dome.
2. The clear (or semi-clear) skin lets light energy in, but traps heat energy.
Even though our dome skin is thin, it keeps the air inside the dome from mixing with the outside air when the wind blows, or a bus drives by. When the sun shines on the dome, lots of the high-energy light can come through the skin. Light goes through space in waves, and the light that helps us see can go right through clear objects, like glass or our dome skin. When the light bounces off the ground inside the dome and plants and the tools, it loses some of its energy. That means that the waves that bounce off can't move as fast as the waves that came into the dome, and they get trapped inside the skin. So while the sun shines, the dome gets hotter and hotter as the energy from the sun gets trapped. And this hot air can't mix with all the other air outside, and level out. That's why it feels so different in the dome. We feel it right away. It's nice in the wintertime, but when it gets hot, we start sweating right away when we walk in.
At night, when it is colder, the air in the dome has to cool off before the ground can start getting colder. We buried a digital light and temperature reader in the middle of our dome, and also hung one up in the air on a string using a pipe cleaner to make a hook. We noticed that the air got colder, then the ground got colder. Also, when the air warmed up, the ground got warmer too.
The hotter air in the dome also means that the air is more humid. Humidity means that there is more water in the air, and it can make it seem even hotter than the real temperature. That's why we seal the wood for the dome real carefully. All the water in the air can make the wood get moldy and rot. When we open our vent flaps all the way, it gets cooler fast. The hot air rises out of the vents, and mixes with the outside air. The water in the air also leaves too, and it feels much better in there. We always see little drops of water by the vents when they are closed. That's because the water comes out of the air when it is near the colder air.
Last thing: We want to warn people who think they can grow anything they want all year round. You can try, but you will end up killing a lot of plants (like we did in our first year dome). There are plants that are good for planting in the cold season, like all the plants in the cabbage family. Their family name is Arabidopsis, so if a plant has that in its scientific name, it is probably good for putting in your dome in the fall.
If you decide to use our instructable and make your own dome, we want to know what you planted!!!!! We grow food for people who can't always buy food on their own. We also go to different community groups and build new domes for them. We are getting pretty good at making these, which is why we thought we would share our experience with everybody. How hot does your dome get? What did you add to make our dome even better? Please let us know.
YES-2-Tech Teens from the Youth Exploring Science Program