Orchids are practically emblematic of fragile, tough-to-grow plants despite the fact that they eke out an existence in leaf litter in their natural habits. Successfully caring for indoor orchids is possible, but getting the potting soil right is key. Ashley Esakin, who has a B.SC in soil science and is known on YouTube as Gardening in Canada, spoke exclusively with House Digest to help readers identify the best soil for their orchids. The first (and possibly most important) thing to know is that not all orchids have the same needs.

“First look at the root size. Size of your pinky or larger means you should be using a chunky mix,” says Esakin. “String size means it’s more of a terrestrial orchid and would do better with potting soil or moss.” Essentially, there are two types of orchids: terrestrial and epiphytes. When you think of an orchid, you’re probably picturing an epiphyte, but terrestrial orchids grow in a more traditional soil. Esakin points to the lady slipper orchid (Paphiopedilum) as an example.

Generally speaking, though, orchid potting mix is largely made up of differing combinations of sphagnum moss, bark or coir, and charcoal. Esakin says there are other clues that will let you know which type of mix you will need. “If a container is enclosed with no holes, is in a cover pot, or is oversized, aim for more bark or coir,” she advised. “If the container is open, slotted, has no cover pot, or is undersized, [then] aim for more moss.”

The three main ingredients of orchid potting soil each have different roles. Moss holds onto moisture. Bark or coir are “…solely used for ensuring there’s air inside of the pot,” said Easkin, but under the right conditions, they can do a bit more. “In an enclosed system or a very humid environment, the bark on its own would likely be enough without the moss,” she said. Charcoal plays a similar role to bark and coir but has added benefits. “The only difference being that charcoal can also hold on to nutrients. This is because of the amount of surface area on charcoal itself,” she shared in her exclusive interview with House Digest.

While there are plenty of orchid potting soil mixes on the market, Esakin thinks you can do better. “Orchid mixes are a good base ingredient for your pots. But I would encourage a person to get the bag of orchid mix, and then add more bark or moss or pine soil as needed based on the above,” she advised. Bagged orchid mix is an easy starting point, but adjusting it to fit the individual needs of your plant will give you a greater chance of success. Speaking of your plants, picking the right plant is a good way to start off on the right foot, so it’s best to get some tips on what to look for when buying an orchid from the store.

There are plenty of mistakes to avoid making when growing orchids, and it’s easy to mistake a dormant orchid for one that’s actually failing. However, if you’re trying to troubleshoot a persnickety orchid, the potting soil may be a problem — and there are some clues to look for. Speaking exclusively to House Digest, Ashley Esakin advised home gardeners to keep an eye out for specific symptoms. “Watch your leaves. If your leaves look wrinkled, then it’s a sign that you are lacking water and may need to increase pot size,” she said. Using a clear pot will give you a good look at the roots, which will give you even more clues to what your orchid needs.

If your orchids with larger roots are brown or mushy, add more coir to your pot. “If the roots on larger orchids look wrinkled, add more moss,” she advised. And if you’re one of those lucky people who have a green thumb, even when it comes to orchids, you will see a bright green tip. This is a sign that your plant is healthy and your soil mix is probably perfect for what it needs.