The intriguing terrarium, or “garden under glass”, makes an impressive gift when filled with a curated selection of mini plants. Often easier to look after than your average houseplant, terrariums are a good idea even for the neglectful gardener. Follow this simple guide on how to make a terrarium for your very own stylish miniature ecosystem.

Invest in these tools to plant up your terrarium. You’ll find more detailed plant and container recommendations below.

Follow this simple guide to achieve terrarium triumph:

Most garden centres and home stores sell glass terrariums in a wide range of sizes and shapes. Choose from miniature Victorian greenhouses to spheres, bottle-shapes or impressive hanging glasses. Alternatively, get creative and upcycle an old goldfish bowl, cloche, mason jar or vase, all of which can be transformed into a terrarium.

Terrariums can be open or closed. The important thing is to select the right plants for your chosen environment. Open terrariums allow more air circulation and so reduce condensation and mould, whereas closed containers open up more planting possibilities, from tropical foliage to evergreen ferns.

Most garden centres stock a wide variety of terrarium-ready plants. Choose various heights and foliage forms for maximum interest, but do make sure they are small enough to squeeze inside your terrarium without touching the sides.

The humid conditions of a closed terrarium open up many planting possibilities.

A fully open terrarium, which offers a low moisture, light environment, is the perfect home for:

…airflow is particularly important for succulents and cacti, so make sure each plant has space to expand.

Add a pop of colour to lush greenery with the following, which grow well in both open and closed containers:

Plants are like humans. For optimum results, you’ll need to meet their food, water, light and temperature requirements.

Open terrariums need a little more watering than their closed counterparts, which retain moisture much longer than potted houseplants. Whichever type you choose, be careful not to overwater. Spritz your plants and the soil sparingly using a spray bottle so that they are damp, but not soaking wet.

Inspect your terrarium fortnightly and water when it starts to feel too dry. If you notice a build-up of condensation you may have added too much water, so remove the top until the condensation dissipates.

Just like your garden and houseplants, terrarium plants hate to sit in water, so drainage holes are a must. Prevent waterlogging by lining your terrarium with a two-inch layer of small stones and pebbles, and add a deeper layer for narrow or tall terrariums. Shells, sea glass and colourful marbles also work well.

The jury is still out on whether to use a fertiliser in a terrarium. While some believe that the natural decay in potting mix provides enough nutrients, many terrarium enthusiasts suggest adding the right plant food for the species you are growing under glass.

Make sure your terrarium has enough light. For both closed and open terrariums, it’s best to place it in an area that receives at least six hours of bright, but indirect, sunlight. In the UK, this could mean placing your terrarium on a north-facing window sill.

Avoid harsh, direct sunlight as a terrarium’s glass will not only magnify the sun’s rays and scorch tender leaves, but it can make the inside temperature too hot for most plants. Natural light is always best, but inexpensive grow lights are a good alternative.

Like Goldilocks, a terrarium needs just the right temperature to survive and thrive. Avoid placing one near a radiator as the atmosphere will be too hot for the hardy plants inside. That being said, make sure your terrarium doesn’t get too cold either. Draughty windowsills and outside locations should be avoided.

Succulents and cacti need a well-drained, porous soil with a generous quantity of sand or grit. Ferns, meanwhile, require a medium density, loam-based compost. If in doubt, ask your garden centre for recommendations.

Make sure to add a good dose of activated charcoal to the mix. Available powdered or in pellets, activated charcoal will remove unwanted toxins, absorb chemicals and keep your terrarium healthier for longer.

It’s a good idea to plan out the design before you start positioning each plant, as moving them from their initial position can cause serious disruption in such a limited space.

Before planting, trim off longer roots to prevent overgrowing. This is essential for maintaining mini plants in a small space. Remove any decayed or yellowing leaves at this stage, and tease apart root-bound plants to give them a head start.

A long spoon can be helpful when digging planting holes and filling them in with potting mix, especially if your glass container has a narrow opening. Chopsticks, tongs and tweezers can also be helpful for placing, pruning and perfecting your plants.

Add a fresh green carpet of moss for the perfect finishing touch that will also help to retain moisture. Natural Sphagnum moss is a terrarium staple. Alternatively, you could use dried or florist moss instead.

Be attentive and trim overgrown plants, including their longer roots, to keep them small.  Always remove yellowing and damaged leaves, as well as dying plants, to prevent the spread of disease and decay.

Regularly remove dust from your terrarium’s glass to allow enough light in for your plants to flourish. Avoid harsh chemical cleaners as these can be harmful to all plants.

Keep a watchful eye out for bugs and pests. Fungus gnats can be a problem and should be removed quickly if spotted. Meanwhile, minuscule springtails are actually a terrarium owner’s friend – these tiny bugs feed on mould and help to keep your terrarium clean, fresh and healthy.

Nicola Clements works at Haddonstone, purveyors of fine cast stone ornaments handcrafted in England. For more information, please visit haddonstone.com.

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