Terrariums aren’t the easiest thing to care for. Especially if they’re filled with cacti rather than typical terrarium plants. Experience is often said to be the best mentor, but this guide will help make your journey easier!
Cacti terrariums require 1) to be open and ideally of 6inchs in diameter or larger, 2) well-draining soil, 3) water when the soil is dry, 4) 8+ hours of direct sun, 5) temperatures between 77–86°F, 5) humidity around 50%, and 6) general liquid fertilizer every month in spring and summer for optimum growth.
Whether you received this terrarium as a gift or made it yourself, it’s important to know how to take care of a cactus specifically inside a terrarium. Ultimately, how you care for your cacti terrarium depends on you, your terrarium, and your environment.
Here is a quick but detailed summary of what your cacti need to thrive inside a terrarium.
Use large, open terrariums. It can be made of plastic or glass and must be big enough to hold the cacti.
Use 50% pumice, 30% coco coir, and 20% worm castings. Soil pH must be between 6 and 7.
Water cacti only after their soil has completely dried out. Use a spoon or syringe for light and careful watering. Reduce watering in the winter.
8 hours of direct sunlight or 10–12 hours under grow lights
77–86°F or 25–30°C. Avoid temperatures under 50°F.
40–50%. Avoid humidity levels over 70–80%.
Use general liquid fertilizer annually or monthly in the spring and summer. Avoid fertilizing in the winter.
Each of these factors is discussed further below, so let’s dive into it!
Large and open terrariums are dry and airy, making them the best container for growing cacti. Ideal materials include glass and plastic.
Part of the beauty of keeping terrariums is the container you use. Closed terrariums are beautiful and may be the first thing you think of.
However, these containers are overly water-retentive and will only suffocate your cacti.
Instead, be sure to use terrariums with large and wide openings. Bowl-shaped terrariums, in particular, retain little-to-no moisture and make it easier for cacti roots to dry out.
Glass is the most common material used for terrariums. Clear plastic can also be used. Terrariums don’t have drainage holes, so you can use pretty much any transparent container you’d like!
For more, check out our article: Can I Use A Mason Jar as a Plant Container? [Definitely But..]
How large of a terrarium you will use depends on the size of your plants. I find that terrariums 6 inches (15 cm) in depth and diameter work wonderfully for 2–3 young cacti.
If you’re looking for something simple, consider this gorgeous geometric glass terrarium on Amazon that’s perfect for holding cacti!
Ideally, it’s easier to work with a terrarium that is too large than one that is too small. You’ll know the cactus is ready to be moved when you see that the cactus is growing uncomfortably big for the container.
Cacti terrariums will benefit from a well-draining mix with 50% pumice, 30% coco coir, 20% worm castings, and pH levels between 6–7. This mix will retain very little moisture, which is key to growing healthy cacti.
Since terrariums don’t have any drainage, it’s best to use an extremely well-draining mix to keep the roots of your cactus from sitting in water.
Soil amendments like pumice and gravel provide plenty of drainage and aeration. Orchid bark is also a common addition, although it takes up a lot of space, which is limited inside a terrarium.
A good mix would be 50% pumice, 30% coco coir or clean cactus soil, and 20% vermicast. The soil pH should be between 6 and 7 for your cactus to grow.
Introducing too much organic matter or compost in terrarium soil can be dangerous for cacti. These ingredients retain too much water and will cause soggy roots.
Pro Tip: Mix and create your soil blend before adding it to the terrarium. This is especially useful for smaller containers or established terrariums that cannot be disturbed.
To ensure adequate moisture while preventing overwatering, use a plastic squeeze bottle or syringe to water cacti terrariums until the soil is moistened. Water them only when the soil is completely dry and no more than once a month in the winter.
Overwatering is the most common cause behind dying cacti and failed terrariums.
Terrariums with puddles of water at the top, bottom, or sides of their soil are holding too much moisture. This excess of water can be fatal for cacti.
Instead, try to provide just enough water to moisten the soil around the cactus. Remember, proper watering is crucial to the health of your cacti. They must only be watered when their soil is 100% dry.
If you’re having trouble navigating small nooks and crannies in your terrarium, a large syringe filled with water can help you water your cacti more accurately.
Alternatively, for a cheap and easy solution, use this plastic squeeze bottle like the one below from Amazon to water your terrariums!
Many cacti go dormant in the winter, so try not to water them more than once every 1–2 months. These plants aren’t picky about what water they receive and will be fine with regular tap water or rainwater.
Cacti in terrariums grow best with a minimum of 8 hours of direct sunlight or 10–12 hours of LED grow lights. It is possible to keep the terrarium with less light, but the cacti will slowly lose their vigor and vibrancy.
Supposing you would rather not encourage growth in a small container, you can keep your terrarium in a semi-low-light area.
But to fully support your cacti and keep them sustained, it’s best to grow them in as much light as possible.
Artificial lights can also be used. They’re much more consistent and easier to control than sunlight, except they require money and space to set up.
We tested and discussed more about grow lights in the article: Grow Lights vs Sunlight: Which is Better? (Tested!) and Are White Lights Good for Plants? We Tested It!
Whatever you decide, it’s best to keep your cactus terrarium in an area with at least 8 hours of unfiltered sunlight or 10–12 hours of grow lights. West or even south-facing windows are perfect.
I must also remind you to consider the needs of your cacti. If your terrarium is filled with different members of the Cactaceae family or consists of grafted cacti like moon cacti, it’s safer to use filtered or dappled sunlight.
Cacti grow best in temperatures between 77°F and 86°F. Avoid exposing the terrarium to temperatures under 50°F for long periods. Most cacti species are not frost-tolerant and will eventually deteriorate and die due to excessive cold.
We’ve learned in a previous experiment that Gymnocalycium cacti can handle temperatures under 40°F without watering. As fascinating as this is, not every cactus can survive such cold temperatures.
Many cacti prefer warm temps within 77–86°F or 25–30°C. As long as the plants aren’t perpetually placed in temperatures below 50°F, your terrarium will be fine.
Some fellow terrarium owners try to keep their cacti in a cool environment to stunt their growth. While this is a clever way to freeze a beautiful cactus display in time and enjoy it for longer, I believe this is detrimental to the health of the cactus in the long run.
If you choose to do something similar or live in a cold climate, reduce your watering completely to keep your cacti alive.
Learn the reason in Can Cacti Survive the Cold? (Cold Damage Signs With Photos)
Many cacti do not need more than 40–50% humidity. Cacti terrariums must not be grown in overly high humidity levels, as this could lead to fungus growth.
Humidity isn’t an important factor when it comes to cacti terrariums. Since these spiky plants are often grown in open terrariums, humidity isn’t much of a concern.
Your favorite desert cacti will probably grow without any issues in humidity levels of around 40%.
However, rainforest specimens such as the holiday cactus or zig-zag cactus will benefit from slightly higher levels above 50%.
The only guideline you should keep in mind is to avoid going overboard. Humidity levels that are over 70% will only increase the likelihood of your cacti developing fungus and infecting the whole terrarium.
Monthly fertilizer applications in the spring and summer are ideal for boosting young cacti terrariums. Use a general liquid fertilizer and avoid feeding during the winter. Contrarily, a cactus can be kept small by fertilizing it only once a year, making it easier to maintain.
Truthfully, I’ve rarely fertilized my collection of cacti, and they’re still green and growing. Despite that, this doesn’t mean you should never fertilize a cactus.
If you’re sowing these cacti by seed or growing younger plants, you can encourage them to fill up the terrarium faster by fertilizing them with a general liquid fertilizer once a month.
Meanwhile, in case you’d rather keep your cacti small, fertilize them no more than once a year. A good time to fertilize is in the spring and summer.
Whatever you do though, never feed your cacti during winter. Unless you have tricked your cactus into believing it is still in its growing season, it will go dormant in the colder months of the year and will not need fertilizer.
Dormant cacti do not need additional nutrients for growth and will be overfertilized if they are fed during dormancy.
At the end of the day, it depends on you, your cacti, and your terrarium. Happy terrarium keeping!
Are terrariums good for succulents?
As long as the terrarium has a large opening and is not completely closed up it can make a suitable environment for succulents. Ensure the terrarium is kept in a sunny spot and only watered when the soil is dry.
Do you have to prune cacti grown in terrariums?
Most cacti species are slow-growing and do not have any leaves. Epiphytic or rainforest cacti have leaf-like stems that can be pruned if necessary, but there is usually no need to prune cacti. If a cactus is too big for its terrarium, it is best to repot it and replace it with a smaller plant.
Cacti terrariums are generally easy and require little-to-no maintenance. But for optimal care, it’s best to grow them in open terrariums with ample airflow. The soil must consist of a minimum of 50% pumice to be well-draining.
Water the cacti terrariums only when their soil has fully dried up. Only provide enough water to moisten the soil. Cacti grow best with 8+ hours of unfiltered sunlight or south-facing windows, but they can also grow under 10+ hours of full-spectrum artificial lighting.
It’s best to keep cacti terrariums indoors where temperatures are around 77–86°F. Cacti do not need humid environments and will grow well in 40–50% humidity. Provide a liquid fertilizer every month in the spring and summer or limit fertilizing to once a year for slower growth.