How to Make a Terrarium

June 17, 2014

How to Make a Terrarium

My husband and I recently took our son to the Brooklyn Botanical Garden to catch a glimpse of the brand-new cherry blossoms. As with most trips with a toddler, ours concluded in the gift shop, which was chock-full of things that made this brown thumb want to get down in the dirt. But what tempted me most was the huge selection of terrariums, a dizzying array of mosses and plants and river rocks, all packaged in nifty glass containers.

To be fair, terrariums are nothing new — virtually every fourth-grade class since the ’70s has tended one — but these days, they’re everywhere: on window ledges, in store window displays, even as centerpieces at dinner parties. And that’s because these mini gardens are undeniably cute, fairly easy to create, and require next-to-no maintenance. (Read: Even a rookie like me can call pull them off, especially instant ones like these.)

But plopping a few random plants in a jar isn’t my thing — I want a terrarium that looks as sharp as the ones in the gift shop. So I called Kerry Michaels, a fearless gardener (“life is too short to be ashamed of killing plants,” she likes to say) and the brains behind’s Container Gardening site. Here are her tried-and-true tips.

Figure out what type of terrarium you want

There are two kinds of terrariums: closed and open. Both are beautiful, and both have very different needs. As Michaels explains it, closed terrariums have a top, and they trap moisture, creating a steamy environment that requires very occasional watering. Humidity-loving plants like ferns and tropicals thrive in this environment. Open terrariums, on the other hand, have no lid and require more frequent watering; for best results, she recommends stocking them with desert plants like succulents.

Stock up on supplies

Terrariums aren’t terribly picky and need just a handful of ingredients to thrive. Plan on buying the following:

  • a glass jar or container with an opening wide enough to fit your hand. Michaels is partial to quirky vessels like martini glasses, mason jarsvotive holders, light fixtures, glass pillars, and cloches.
  • sterile potting mix.
  • activated charcoal, available at nurseries or pet supply stores.
  • moss, gravel, glass beads, sea shells or stones to disguise potting soil.
  • low- to medium-light plants that are small enough to fit inside the container without touching the sides. Michaels is a big fan of the polka dot plant, Prayer Plant, Baby’s Tears, Croton, and small ferns — “they’re bulletproof,” she says.
  • small figurines to tuck in between the foliage (optional).

Come up with a design

Since it’s encased in glass, your terrarium can be viewed on all sides. To get a gorgeous 360, Michaels suggests using plants of different sizes, leaf textures, and color. Play around with placement until you find an arrangement you like, then dig the holes. Not sure where to start? Place taller plants in the middle and work outward from there. If you prefer a minimalist look, try positioning one eye-catching plant just slightly off-center and surrounding it with gravel or crushed glass. Whatever the final design, “go for instant gratification,” she says. “You want it to look good from day one.”

Plant the terrarium

Fill the container with a nest of moss or a layer of rocks for drainage, and then add about a half-inch of activated charcoal, Michaels says. Cover with more moss, and then top with pre-moistened potting mix. Make a small hole with a spoon or your fingers, and then drop in your plants. Fill in any empty spaces between plants with moss. Finish by spritz the soil with water until just damp.

Keep it healthy

If maintained properly, a terrarium can outlive most of your household pets. To help yours go the distance, avoid these common mistakes:

  • Too much water. “Just give it drips of water when the soil is dry to the touch,” Michaels recommends.
  • Too many plants in the terrarium. Bunching is okay; leaves sticking to the glass — not so much.
  • Too much/too little sunlight. “It gets so hot in a terrarium, you don’t want to put any of them in direct light,” she explains. That said, the amount of sunlight required depends on the plants you buy, so consult the care instructions.

Bonnie Vengrow

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