One of the main problems that people experience with plant terrariums is fogging. But why do terrariums fog up? In this post, you will learn why terrariums are fogging and how to keep a terrarium from fogging.
Fogging up in a terrarium is normal. In general, there are few factors that determine how often and how intensely your terrarium fogs up. If the fog is not causing a lot of actual water drops, then you might want to open the lid or wipe the terrarium sides.
Fogging in a closed terrarium
If you have a closed terrarium and it’s fogging, it will be mainly caused by too much water and differences of temperature inside and outside of the terrarium.
If for example, direct sunlight hits the closed glass terrarium, the temperature inside the terrarium becomes too high. That will lead to fast water evaporation and will also cook your plants or severely burn them.
Most plants that you use in a terrarium – succulents, air plants, and even tropical and carnivorous plants, love bright but indirect light. You should only plant most of them in an open terrarium. That’s because they need proper ventilation and will die in a closed terrarium.
But even if you use mosses, ferns and other higher humidity loving plants in a closed terrarium, you should still be careful. Most of those plants also don’t like constant or even any direct sun.
Even shape of the terrarium might make your terrarium fog more. Lidded round jars tend to fog more. To prevent fog in a closed terrarium, you will need to open the lid once a week for around 24 hours to let the condensation clear.
When leaving the lid open, make sure that the air is not too dry in the spot where your terrarium is. In general, try not to move the terrarium around too much.
That’s when conditions change dramatically and suddenly. Moving a terrarium is fine once in few weeks if seasons change or if you want to take it outside for fresh air circulation.
However, you should turn your terrarium once a week or so, so that every part of the plant can receive sunlight. Otherwise, your plant will start leaning to one side.
Fogging in an open terrarium
If you notice fogging in an open terrarium, it could be due to overwatering. Before you water your terrarium, make sure the soil is dry. As your terrarium doesn’t have drainage holes, you must be careful with how much and how often you water your terrarium.
You can read a terrarium watering guide here.
Same as with closed lid terrariums, don’t place them in direct sunlight. Direct sunlight will increase temperatures in the terrarium and water evaporation. You can place the terrarium near the window, but aim for indirect filtered light (or maximum few hours of direct light for open terrariums with succulents and carnivorous plants).
How to keep a terrarium from fogging?
To stop the terrarium from misting/fogging, you can review your watering schedules, as well as terrarium positioning.
Try to position your terrarium in a spot where bright indirect light is present for the most of the day. That will help prevent temperature differences inside and outside of your terrarium.
Most often, a terrarium fogs up when temperatures in the house drop after a warm day. In this case, to avoid fogging, you can heat the terrarium a bit by having a lamp or similar near it. This can be a general desk lamp, but make sure not to position it too close to your terrarium.
You can also use a fan to help get rid of fog in the terrarium. Because air exchange is also important, make sure to open the terrarium lid for 24 hours once a week. If it’s mainly a self-sustained terrarium, you can open the lid once a month for few days in a row.
Warm air rises up, so having a small open gap on the top of your terrarium (around 1 inch) is enough to clear the condensation. Please remember, that fogging is generally normal and often doesn’t cause any negative consequences unless the humidity is too high.
If you see fog/misting in a terrarium and it goes away the next day, there is not much to worry about. If you really want to see the terrarium contents, use the light and heat as described above.
While you can use anti-fogging sprays to prevent fogging of the terrarium glass, it’s not recommended. Because your plants are in a small mostly enclosed container, it can harm them.
Fogging and watering terrarium plants
Fogging, especially in a closed terrarium, is perfectly normal. However, to prevent fungus and rot, you must not overwater your terrarium plants. Closed terrarium plants don’t need much watering at all, all due to the same condensation.
Closed fish tank, globes, apothecary jars often don’t need misting or water at all. However, once in 6 months or so, you can wipe the glass and slightly mist the terrarium.
Cloche and Wardian case terrarium plants might benefit from some misting once a month or so. Open terrariums will often benefit from watering once in 7-10 days, or up to 2 times a week in summer.
Please make sure that the soil dries between waterings (especially for succulents), and always touch it to see if it’s dry. If it’s not dry, don’t water. But if you accidentally overwater your plants, use a paper towel to absorb any excess water.
Thanks for reading this post on terrarium fogging and condensation. To read more about watering your terrarium and condensation, see this post.