Stop Calling Every Glass Planter a "Terrarium”

“If it doesn’t have a lid, who you trying to kid?”

By Gregg “Roosevelt” Harris,
Owner/Proprietor of Roosevelt’s Terrariums at 44th & Hawthorne

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 not true. Being sealed is essential. A terrarium by definition is a closed, self-contained, recycling ecosystem. What makes a terrarium work is the fact that it is closed off from the harsher environment surrounding it. That is why you can grow things in a 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.

They've got to have a lid.

An early Wardian Case

That is the terrarium that Dr. Nathaniel Bagshaw Ward discovered in 1827 London, England. He found a delicate fern growing happily inside a closed jar— in spite of all the soot and smoke that was spewing from the factories near his neighborhood. Ferns would not grow in London during the Industrial Revolution. Dr. Ward’s first terrarium worked because it had a LID. It was closed. He had discovered what we now know as “the terrarium effect”  and it was the basis for the design of his “closely glazed” Wardian Cases.

Does the Lid Really Matter All That Much? Yes.

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 evaporated 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 person at the grocery may tell you, all houseplants need light. Some need less than others, but all need light.

This is why I am declaring war on all the misinformation surrounding terrariums, starting with the lid. A terrarium must have a lid of some kind, 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 terrarium.”

Is this misunderstanding widespread? Unfortunately, yes. As I said, Wikipedia still has it wrong. (I hope to use a reference to this column as the basis for correcting their article. Watch the listing for the change.)

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 terrariums, because they do not have a lid. They are glass planters with wide gaping openings that allow all the plant’s water to quickly evaporate away.

A Feature Or a Benefit?

A closed system is more than just a terrarium feature, it is a real terrarium benefit. A properly planted terrarium with a tightly fitting lid can grow for decades without even being opened.  Some may never need to be watered ever, because they keep using the same water and air over and over again. Place them in bright, indirect light, maintain moderate temperatures between 60 and 85 degrees, and they will remain healthy and beautiful for years and years. So, yes, I would certainly consider that to be a benefit.

That is why I can afford to back up my terrariums with a guarantee. My terrariums have lids.

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