Mad About Science


By Brenden Bobby
Reader Columnist

I’ve said it before and I’ll say it again: plants are amazing.

Some plants have adapted to live for an unfathomably long time — think about Pando, the 108-acre aspen clone that is at least 80,000 years old. You’ve seen me muse time and time again about how awesome it is that plants can easily graft on the limbs of other plants, as you may have seen in the six-way apple trees available in most nurseries.

You can even seal a plant in a jar and watch it grow for decades.

Courtesy photo.

A completely sealed ecosystem in which a plant exists is called a terrarium, and the size of a terrarium can vary from a simple mason jar to the world’s largest, a 2,000-pound “forest in a jar” in Poland. That’s right: The same Poland that inspired The Witcher series, with a climate not too dissimilar from our own here in North Idaho, also houses a massive jar full of tropical plants that are completely self-contained and thriving.

A terrarium and a greenhouse are both designed with similar principles in mind. A layer of transparent plastic or glass allows light to pass through. Upon striking a surface, some of the light is reflected away, while the rest is absorbed and converted into heat energy. Darker objects absorb more light, which creates more heat. That’s why the black leather seats in your car feel as though you’re sitting on the surface of a stove this time of year. Back to the topic at hand: The short wavelengths of light easily pass between the molecules of glass, but the longer wavelengths of heat cannot.

This is called a “greenhouse effect” and it can even happen at a global level. Plastic sheeting is made out of precisely configured molecules of carbon, hydrogen and oxygen, which are also naturally abundant in our atmosphere. Industrial and automotive applications produce aerosolized carbon monoxide, which is one part carbon, one part oxygen. As it comes together en masse, it acts like the plastic sheeting of a greenhouse, allowing sunlight to pass through, but limiting the amount of heat that can radiate off the planet’s surface and back into space. As more and more fuel is burned, more carbon monoxide is released and creates a thicker insulating layer, allowing less and less heat out.

Now think about how those processes apply to a terrarium. To exist, plants require three factors: water, nutrients and light. A proper terrarium houses both water and nutrients — as well as the plant — while the sun provides the light. You may wonder how a plant will get new nutrients and water when it’s sealed in a glass jar, and put simply: it doesn’t need to.

Plants are great at recycling. In the wide open world, nutrients get used up when a plant creates fruit and seeds, which will usually be carried off and deposited somewhere else by wind, water or animals. This allows the plant’s offspring to find a new place to grow with fresh nutrients and other plants that don’t share the same genetics. In a terrarium, the nutrients don’t have anywhere to go, so the plant can just repeatedly use the same set of nutrients over and over again.

The same is true of water. Water is a delicate thing, existing in its vital liquid form at a very precise temperature range between 32 degrees Fahrenheit and 212 degrees Fahrenheit. Compare this for a moment to the surface of Venus, which hovers around 900 degrees Fahrenheit — hot enough to evaporate water instantaneously. It’s this delicate trait of water that allows a terrarium to sustain a plant. As sunlight hits the water and heats up the surface, the molecules begin to evaporate; however, since they’re trapped inside a glass jar, they have nowhere to go and will begin to coalesce near the top to “rain” back down onto the plant.

This “contained garden” was popularized by an image that occasionally makes the rounds on social media of David Latimer and his 10-gallon spiderwort-in-a-jar. Though spiderwort may be a hardy plant, it’s not the only type of flora that thrives in a terrarium.

Thinking of making your own terrarium? Self-contained gardens can make wonderful and attractive hobby pieces while remaining extremely low maintenance.

Here is all you need to get started:

• A jar or glass case. The objective is that you must be able to keep the container airtight once everything is assembled;

• Enough rocks or pebbles to cover the bottom, as well as enough peat moss and topsoil to fill one-third of the jar;

• A seed or cutting of your choosing — keep the size of container in mind, you don’t want to have a cedar tree growing in there;

• A little bit of water. Enough for the plant to grow, but not so much that it drowns it.

Simply create a layer of pebbles across the bottom of the jar, place your peat moss and topsoil overtop of the rocks, pour in your water and plant your seed. For the first two weeks, you may want to cover the spout of the jar with something like a rubber glove to keep it airtight while you gauge whether or not the plant will need more water. If the plant seems happy after two weeks, replace the rubber glove with a permanent seal and enjoy your no-maintenance houseplant.

If you’re really feeling creative, try planting multiple types of plants and see which ones thrive the best in this setup. After that, sit back, relax and enjoy the fact that you’re doing the same work that astronauts are doing on the International Space Station.

Stay curious, 7B.

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