Watering a terrarium is kind of an art. You’re not following a calendar, and you’re definitely not soaking the soil like you would with a houseplant. Instead, you’re paying attention to subtle signs—because terrariums are all about balance.

Some setups can go months (or even years) without a top-up. Others need a gentle mist every couple of days or weeks. So how do you know when to water?

Let’s break it down.

There’s no one-size-fits-all schedule

The short (and slightly annoying) answer to “how often should I water my terrarium?” is:

Only when it needs it.

That might mean once a month. Or once a year. Or barely ever, if you’ve built a well-sealed setup with the right plants.

Terrariums are excellent at holding onto moisture—but only if you respect their limits. The goal isn’t to keep the soil wet. It’s to create a stable environment where moisture recycles slowly and predictably.

The best watering tool: a mister

If you're only going to remember one thing from this article, make it this:

Use a mister, not a watering can.

A fine spray distributes moisture gently, evenly, and safely. It prevents overwatering and helps maintain a balanced humidity level, which is especially important for mosses and tropical plants.

I use distilled water for misting. Rainwater or reverse osmosis water also works. Tap water is usually okay, but it can leave mineral buildup over time, especially in sealed setups or if you have hard water. If you want to play it safe, stick with distilled.

Signs your terrarium needs water

Don’t rely on a schedule. Look for these signs instead:

1. Dry soil

The most obvious clue is crumbly, dry-to-the-touch soil. If the top layer looks pale or dusty, it’s probably time for a light mist or a small top-up. You can check deeper soil by gently inserting a chopstick or skewer—if it comes out dry, your plants likely need hydration.

2. Dry or crispy moss

Moss is a great moisture indicator. If it feels crunchy, dull, or grayish, your terrarium’s humidity is too low. Healthy moss should feel soft and look vibrant green.

3. No condensation

In balanced terrariums, you’ll often see light condensation on the glass in the morning. If you've seen zero condensation for a few weeks, that could be a sign it’s time to reintroduce moisture.

4. Wilting or drooping plants

Leaves that start to droop, curl, or feel soft instead of firm are often a sign of dehydration. This is common in fittonia, pilea, and ferns. Just don’t confuse natural growth changes with distress—context matters.

5. Brown or dry leaf edges

Crispy leaf tips and dry edges a telltale sign your plants aren’t getting enough moisture. These symptoms usually show up gradually, so catch them early if you can.

6. Slowed or stunted growth

Healthy plants keep growing. If your terrarium seems frozen in time (and it’s getting enough light), lack of water could be the culprit.

7. Leaf drops

Underwatered plants may start shedding their leaves. Older leaves go first, but severe cases might affect newer growth too. If you're seeing a lot of leaf drop, check the soil and moss conditions immediately.

Signs you’ve overwatered

Terrariums are closed (or semi-closed) systems. That means excess water doesn’t drain away—it just lingers. And that can lead to bigger problems than dryness.

Watch out for:

• Constant, heavy condensation on the glass

• Mushy stems or blackening leaves

• Mold growth on soil, wood, or moss

• Fungus gnats buzzing around the container

• Plants turning soft, translucent, or discolored

These are classic signs of overwatering and/or poor airflow. If you see any of them, pause before adding more water.

If you think you've gone too far, take the lid off (if there is one) and let the terrarium air out for a day or two. Remove any dying plant material and monitor closely before sealing it again.

So... when should you water?

Here’s a simple rule of thumb:

• If multiple signs point toward dryness—dry soil, dry moss, drooping leaves, no condensation—give your terrarium a gentle mist.

• If you’re only seeing one minor sign, hold off and check again in a few days.

Start small. You can always add more later, but once the water is in there, it’s hard to take back.

How much water is enough?

Think of it in layers.

• A light mist across the surface is often all you need for maintenance

• If the soil is very dry, you can add a few teaspoons of water at the base using a squeeze bottle or pipette

• Don't pour water directly into the terrarium (unless it's a bog terrarium)—it’s the fastest way to drown your ecosystem

After watering, watch what happens over the next 24 hours. You should see a bit of new condensation or a slight perk-up in your plants. If not, add another small round of misting.

Final thoughts: trust observation over routine

The biggest lesson I’ve learned after years of building and maintaining terrariums?

Observation beats routine, every time.

You don’t need a fancy moisture meter or a strict schedule. You just need to know what to look for—and give yourself permission to not water if things are already in balance.

Terrariums are meant to be low maintenance. Once you learn to read the signs, they’ll practically take care of themselves.