Terrarium Design: Teaching Kids Ecology and Systems Thinking

In 1960, a man named David Latimer planted a spiderwort cutting in a glass bottle, watered it, and sealed the stopper. He opened it once in 1972 to add a small amount of water. He has not opened it since. As of 2023, the plant is still alive — over 60 years of continuous growth in a sealed, self-sustaining ecosystem no bigger than a beach ball. The water in the bottle has recycled itself thousands of times. The oxygen produced by photosynthesis and consumed by respiration has balanced. The decomposing plant litter has been recycled by microorganisms back into nutrients. It’s a closed ecological system on a kitchen shelf.

A closed terrarium is the most vivid demonstration of ecosystem principles available outside of a university ecology lab. The water cycle, carbon cycle, nutrient cycle, and interdependence of producers and decomposers are all happening in a glass jar that a kid can watch and touch. Building one teaches systems thinking — the understanding that everything in a system affects everything else — in the most direct way possible.

Key Takeaways

• A closed terrarium demonstrates the water cycle, carbon cycle, decomposition, and nutrient cycling in a sealed, self-sustaining system
• Open terrariums teach basic plant care; closed terrariums teach ecosystem science — both are valuable but for different reasons
• Total cost: $10–25 using a glass jar from a dollar store and a few small plants
• Kids learn the concept that everything in an ecosystem is connected — changing one element affects all others
• Ages 8+ can build and maintain a terrarium with guidance; ages 12+ can design it as a systems experiment with measurable variables

What a Terrarium Actually Teaches

There’s an important distinction between a “terrarium as decoration” and a “terrarium as an ecology lesson.” The decorative version — plant in a glass container — is fine. The educational version requires understanding what’s happening inside, and why.

In a properly built closed terrarium:

The water cycle: Moisture from the soil and transpiration from plant leaves condenses on the cool glass walls, runs down, and soaks back into the soil. In the morning (when the glass is cooler), condensation is visible as droplets. In the afternoon (when the light warms the air inside), the droplets evaporate. This is precipitation, evaporation, transpiration, and condensation — the complete water cycle in a 12-inch jar.

The carbon cycle: Plants absorb CO₂ from the air inside the jar during photosynthesis and release O₂. At night, the same plants respire (like all living things), consuming O₂ and releasing CO₂. Bacteria decomposing plant litter also produce CO₂. In a balanced system, these fluxes equilibrate. The terrarium’s glass trapping effect is a literal demonstration of the greenhouse effect.

Decomposition and nutrient cycling: Dead plant material (fallen leaves, dead roots) is decomposed by bacteria and fungi in the soil. The decomposition releases nitrogen, phosphorus, and other nutrients back into the soil in forms plants can absorb. Without decomposers, nutrients would accumulate in dead matter and become unavailable to living plants.

Systems interdependence: Remove the decomposers (by sterilizing the soil) and the plants will eventually exhaust soil nutrients and decline. Remove the plants and CO₂ accumulates (from decomposer respiration) with nothing to consume it. Every element depends on every other element — that’s systems thinking.

Open vs. Closed: What Each Teaches

Feature	Open Terrarium	Closed Terrarium
Maintenance needed	Periodic watering	Near-zero once balanced
Demonstrates water cycle	Partially	Fully (condensation visible)
Demonstrates decomposition	Partially	Fully
Duration	Indefinite (with care)	Months to years without intervention
Best for teaching	Plant care, soil types	Ecosystems, cycles, self-regulation
Best plants	Succulents, cacti (low moisture)	Ferns, moss, tropical plants (high moisture)
Risk of overwatering	Moderate	Low (excess drains through layers)
Cost	$10–20	$15–25

What to Build

The Sealed Ecosystem Terrarium

Materials:

• Glass jar with tight-fitting lid (mason jar, large candy jar, carboy — minimum 1 gallon for stability) | $5–15 or free
• Activated charcoal (prevents bacterial odor buildup) | $3–5 (aquarium section of pet store)
• Coarse sand or gravel (drainage layer) | $2–3
• Potting soil (not garden soil — too dense; use sterile potting mix) | $3–5 for a small bag
• Small plants: moss (from the yard or a florist), small ferns, baby prayer plants, or any small tropical plant | $2–6 each
• Small rocks, bark, or figurines for decoration | Optional, free
• Water (dechlorinated tap water or distilled) | Free

Layer order (bottom to top):

1. ½ inch gravel or coarse sand (drainage)
2. ¼ inch activated charcoal (filtration, odor prevention)
3. Thin layer of sphagnum moss (separates charcoal from soil, prevents mixing)
4. 2–3 inches of potting soil
5. Plants (planted firmly)
6. Optional top dressing of moss or small rocks

Water carefully: Add only 2–4 tablespoons of water after planting. The system should be lightly moist, not wet. Too much water in a sealed system creates rot.

Seal and observe: Close the lid. Place in indirect light (direct sun overheats a sealed jar quickly). Over the first week, watch for condensation patterns. Condensation every morning and clearing by afternoon = properly balanced moisture. Constant fog with no clearing = too much water (open briefly to let some evaporate). No condensation ever = too dry (add a small amount of water).

When it’s balanced, leave it alone. That’s the point: a functioning ecosystem manages itself.

How to Teach Your Kid About Ecosystems Through Terrarium Building

Ages 8–10: Build and Observe the Water Cycle

Build the closed terrarium together. Each day for two weeks, ask your kid to observe and write one sentence: “Today the glass has [condensation description]. The plants look [description].” Draw the condensation pattern. On day 7, discuss: “Where does the water come from?” (Plant transpiration + soil evaporation.) “Where does it go?” (Back into the soil.) “Did we add any water?” (No.) “So where does the water keep coming from?” This is the moment the water cycle concept crystallizes — they’ve been watching it happen for a week.

Ages 11–12: The Manipulated Variable Experiment

Build two terrariums simultaneously: one sealed, one open (same plant species, same soil volume, same initial watering). Measure both once a week: soil moisture (insert a finger to the second knuckle — is it moist, damp, or dry?), plant height, new leaf count, and overall plant health (1–5 scale). After 4–6 weeks, compare the data. The closed terrarium should require no additional water; the open one will need watering periodically. Ask: “Why does the closed one not need water?” The answer requires understanding the water cycle.

Extension: Add a thermometer inside each. Measure temperature at midday. The closed terrarium will run 2–5°F warmer due to the greenhouse effect — CO₂ and water vapor trap thermal radiation. This is a miniature demonstration of why CO₂ levels affect planetary temperature.

Ages 13+: Design for Biodiversity

Design a terrarium to maximize species diversity. Research the concept of niche differentiation: in a functioning ecosystem, different species occupy different ecological niches (roles), which reduces competition and allows more species to coexist. Try to include: a ground-level moss (decomposer habitat), a mid-level fern (primary producer), a small vine for vertical growth (uses different light angle), and perhaps a small piece of bark (microhabitat for fungi and detritivores if any naturally colonize). After 4–6 weeks, count the number of distinct organisms you can see (including any mold, fungus, or small insects that may have colonized). Is the more diverse system more stable?

The question to ask: “If you opened the terrarium once a week, what would eventually happen — and why?”

The Systems Thinking Connection

Systems thinking is one of the most valuable cognitive frameworks for navigating complexity — in engineering, ecology, economics, and management. It’s the recognition that:

• Systems have feedback loops (plant growth → more transpiration → more available water → more plant growth)
• Changing one element changes many others
• Simple rules can produce complex, emergent behavior
• Systems can self-regulate (homeostasis)

The terrarium demonstrates all four properties in a physical, observable system. The sealed lid is important: a closed-loop system with no external inputs or outputs is the clearest demonstration of recycling and self-regulation.

The biosphere itself is a closed system in this sense (except for sunlight input and radiated heat output). David Latimer’s bottle is a metaphor for Earth. NASA researchers studying closed life support systems for long-duration space missions (where astronauts must recycle water, oxygen, and nutrients) use the same principles. The terrarium is small-scale astrobiology.

What to Watch For Over the Next 3 Months

Month 1: Condensation patterns stabilize. A healthy sealed terrarium develops a predictable daily pattern: morning condensation, afternoon clearing. If it stays foggy or dries out completely, something is off. Adjust water level and observe change.

Month 2: Decomposition becomes visible. Old leaves on the soil surface may develop white mycelium (fungal threads) or appear darker as they decompose. This is the nutrient cycle in action — not decay, but recycling. Point it out explicitly.

Month 3: Moss may spread to new surfaces. The plants may show new growth in unexpected directions (phototropism — growing toward light). The terrarium is adapting; it’s a living system with ongoing dynamics. Ask: “What’s different now compared to month 1?”

Red flag: black or brown mold with unpleasant smell indicates too much moisture and anaerobic (oxygen-free) decomposition. Open the lid, remove any visibly rotting plant matter, allow to dry slightly, then re-seal.

Frequently Asked Questions

What plants work best in a sealed terrarium?

Mosses and ferns are the gold standard for closed terrariums: both thrive in high humidity, tolerate low light, and grow slowly enough to not outgrow the container quickly. Good options: Java moss, cushion moss, button ferns, maidenhair ferns, and small peperomias. Avoid: succulents and cacti (too low moisture tolerance), fruiting plants (too large), and plants that require direct sun.

Can we add animals to the terrarium?

Small isopods (pill bugs, “roly-polies”) and springtails are commonly added to terrariums and serve a real ecological function as detritivores — they eat dead plant matter and help decomposition. Both are harmless, tiny, and widely available. Snails are sometimes added but can quickly overpopulate. Insects, frogs, and other animals require much more careful management and much larger volumes; don’t add them to a sealed system.

How long can a properly built closed terrarium last?

David Latimer’s bottle plant has lasted over 60 years. Well-built terrariums using the right plants, correct moisture levels, and indirect light routinely last 5–20+ years. The limiting factors are usually: too much direct sun (cooks the plants), too little light (plants die), or initial over-watering causing root rot.

Is indirect light different from shade?

Indirect light means bright light that doesn’t hit the terrarium directly — near a north-facing window, or a few feet from a south-facing window, or behind a sheer curtain. Shade (under a staircase, in a dim hallway) may not provide enough light for plant photosynthesis. The test: can you comfortably read a book by the light in that spot without a lamp? If yes, there’s probably enough for a terrarium.

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About the author

Ricky Flores is the founder of HiWave Makers and an electrical engineer with 15+ years of experience building consumer technology at Apple, Samsung, and Texas Instruments. He writes about how kids learn to build, think, and create in a tech-saturated world. Read more at hiwavemakers.com.

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Sources

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3. NASA Life Sciences. (2022). Controlled Ecological Life Support System (CELSS) Research. https://www.nasa.gov/feature/advanced-closed-loop-life-support-systems
4. Tilman, D., et al. (2001). “Diversity and Productivity in a Long-Term Grassland Experiment.” Science, 294(5543), pp. 843–845. https://doi.org/10.1126/science.1060391
5. National Science Foundation. (2022). Ecosystem Sciences in K–12 Education. https://www.nsf.gov/pubs/2022/nsf22060/nsf22060.pdf
6. Meadows, D. H. (2008). Thinking in Systems: A Primer. Chelsea Green Publishing. (Systems thinking foundational reference for educators.)