Terrarium Troubleshooting

You cannot tell from the leaves, and this is the central problem the book is built around.

Both conditions produce drooping. Fittonia can wilt conspicuously when dry — and wet conditions can equally accompany root failure, which also makes plants droop. So leaf posture tells you that something is wrong, not which thing.

The check is physical. Look at the stem, the roots and the substrate before doing anything. Some plants, Fittonia included, recover turgor after appropriate watering when they were genuinely dry; that does not mean every limp plant is thirsty, and it certainly does not mean dead tissue will turn green again.

It is worth knowing that Fittonia albivenis’s habit of wilting visibly is double-edged. It is a helpful early signal, and it is the reason this particular plant is overwatered more than any other terrarium species — because the signal gets read in only one direction.

Some is normal and expected in a closed jar. The question is whether it clears.

The sequence when there is clearly too much is to check the root zone and recent watering first, then remove accessible excess with a clean cloth, or briefly open the lid while watching the plants — then recheck after the jar has returned to its usual conditions.

Framing venting as a measured correction rather than a routine is the important part. Treating daily opening as maintenance converts a closed system into an open one that dries, gets watered, and arrives at the saturated substrate you were trying to avoid.

Light interacts with this more than people expect. Use the fixture maker’s placement guidance, assess what the plants actually need, and check for heat at the jar — a lamp placed close enough to warm the glass changes the condensation behaviour of the whole container. A timer provides repeatability, and the roughly 12-hour period this guide uses is an editorial starting routine rather than a species-specific optimum.

No. They are a sign that there is moist organic material, which there always is.

Springtails commonly occur in moist organic matter and many feed on fungi and decaying material; some species feed on living plants. Their presence does not repair saturated roots and does not prove a jar is balanced — a claim repeated widely enough in terrarium hobby circles to be worth contradicting directly.

Fungus gnats need a different correction from the one people usually apply. The soil-dwelling stages and the adult flies are different targets, so an adult trap catching flies does not establish that the problem is resolved; it establishes that there are adults.

While investigating, keep the jar away from other houseplants, remove accessible decaying material and review the wetness of the substrate. And before any tool goes in, remove visible soil and plant debris from it — if disease or pests are suspected, follow a suitable tool-disinfection product label, and avoid carrying treatment residue back into the jar.

Start by establishing that it is moss.

Selaginella, sold as spike moss or clubmoss, is a vascular plant and not a true moss. It can be perfectly suitable for a terrarium, but it has its own growth and care requirements, so care advice written for mosses will not necessarily keep it alive — and a great many terrarium failures attributed to moss are actually Selaginella being treated as something it is not.

That identification problem runs through the plant pages generally, which is why the manual includes plant-specific profiles rather than one set of terrarium rules. A jar typically contains several species with different tolerances sharing one atmosphere, and the one that declines first is usually the one furthest from its own requirements.

So the diagnostic order is species first, then conditions, then the symptom.

No. The other guide builds three displays to measured plans with shopping lists and assembly steps. This one assumes the jar already exists and something is going wrong in it. They are diagnosis and construction respectively, and this book does not repeat the build specifications.

Fourteen tables organised by what you can see — drooping, fogging, white deposits, mould, leaf loss, insects — each naming the likely causes, what to inspect next, and the page that explains it. They are arranged by observation rather than by cause, because the observation is what you actually have.

Yes, with profiles for the species commonly sold for closed jars, including Fittonia, Selaginella, a tongue fern and Pilea. The point of the profiles is that a mixed jar holds plants with different tolerances, and the one declining is usually the one furthest from its own requirements.

No, and it says why. The correct amount depends on the jar, the substrate, the plants and the light, none of which it can see. What it gives you is an inspection order — stem, roots, substrate, recent history — so that you act on evidence rather than on leaf posture.

No interior illustrations. The cover is the only image in the file; everything inside is text and symptom tables. The cover is an illustrative image rather than a reference photograph of a diagnosed terrarium.

Nineteen are listed with links and descriptive notes, and seven are cited inline. This page prints both figures rather than the larger one. The twelve uncited entries — extension and RHS pages on terrariums, waterlogging, salt deposits and individual species — are the reading behind the plant pages, but inline support is what can be checked, so seven is the number the book is sold on.

No specific products. Where disinfection or pest treatment comes up it directs you to follow the label of a suitable product, because what is approved and sold differs by country and changes. It is not a treatment manual.