Stop calling every glass planter a terrarium! A lesson from Roosevelt’s Terrariums

Published 12:00 am Wednesday, February 24, 2016

I’m sorry, but Wikipedia has got it wrong. There you will read, “Terrariums are usually sealable glass containers.… However, this is not essential; terrariums can also be open to the atmosphere rather than being sealed.”

That is simply not true. Being sealed IS essential. A terrarium, by definition, is “a sealed transparent globe or similar container in which plants are grown.” It is a closed, self-contained, recycling, ecosystem. What makes “the terrarium effect” work is the fact that it is closed off from the harsher environment surrounding it.

That is why you can grow so many wonderful things in a true terrarium that you cannot grow out in the open. A terrarium supports the tropical and woodland plants inside by protecting them from cold drafts, dry heat and poor air quality.

This closed version of a terrarium is what Dr. Nathaniel Bashaw Ward discovered in 1827. An amateur botanist living in London, England, he found a delicate fern growing happily inside of a closed jar— and that in spite of all the soot and smoke that was spewing from the factories near his neighborhood. Such ferns would not grow in London, England during the Industrial Revolution. SO this was an amazing discovery.

Dr. Ward’s first terrarium worked specifically because it had a lid. It was closed. He had discovered what we now know as “the terrarium effect.” It provided the scientific basis for the design of his “closely glazed” Wardian Cases that transported delicate plants around the world.

Does the Lid Really Matter All That Much? Yes, it Does.

Inside every terrarium there are two vital cycles going on. The first and most noticeable is the water cycle. A small amount of water in the soil is being taken up through the roots of the plants and evaporate out through their leaves to be condensed on the cool sides of the glass container where it then trickles down the sides and back into the soil. If you open a terrarium “just to clear up the foggy glass” you just interrupted its water cycle. Please don’t do that.

The other cycle is an exchange cycle between the live plants and the microorganisms residing in the soil. The plants need the carbon dioxide that the microorganisms produce and the microorganisms need the oxygen that the plants produce. This is a mutually beneficial relationship by which both thrive. But if you take the lid off for too long, this cycle also will be interrupted.

The only thing that your terrarium needs from the outside is the energy provided by bright, indirect sunlight. All plants need light, whether natural or artificial, in order to complete photosynthesis. So, regardless of what the nice person at the grocery may tell you, all houseplants need light. Some may need less than others, but all need light.

When you Google the word “terrarium” you bring up thousands of pictures of beautiful glass containers planted nicely with all kinds of plants. Many of them are stunning. But, five out of six of them are not true terrariums, because they do not have a lid. They are glass planters with wide gaping openings that allow all of the plant’s water to quickly evaporate away.

Optional Feature Or Primary Benefit?

This closed system of a terrarium is more than just an optional feature, it is the primary benefit of being a terrarium. A true terrarium, one with a properly fitting lid, can grow for decades without being opened. Some may need a few ounces of water every 2 to 3 months. Others never need to be watered, ever, because they keep using the same water and air over and over again. Just place them in bright, indirect light, maintain a moderate temperature between 65 and 85 degrees, and they can remain healthy and beautiful for years and years.

Terrariums are a great way to enjoy plants if you do it right. So, I am declaring war on all the misinformation surrounding terrariums, beginning with the importance of have a lid. If you want to enjoy all the benefits of owning a terrarium, it must have a lid of some sort, whether it be a glass lid, a tightly fitting cork, or a screw on cap.

Just remember this little rhyme, “If it doesn’t have a lid, who you trying to kid? It’s not a true terrarium.” I could never afford to back up my terrarium plantings with free maintenance and free replanting if my terrariums did not have lids. But with a lid, I can, and I do.

In my Terrarium Classes on Tuesday and Thursday evenings, we get into all of this and more. The results of doing it right are on display all over my shop. I hope you will stop by to see what a difference one little lid can make.

Roosevelt’s Terrariums

1510 SE 44th Ave, Unit. 101, Portland, OR 97214

(503) 734-9996

http://www.rooseveltspdx.com