Gardening: do I need a drainage layer?

Some people have been arguing for 25 years about whether Jack had room to get on the board or whether Ross and Rachel were really broken up. At Monstera, we're passionate about a completely different topic: Should you add a drainage layer when repotting your plants? We've compiled the arguments from both supporters and opponents of clay pellets at the bottom of the pot so you can make up your own mind.

A few centimeters of mineral material that's setting the web ablaze

A drainage layer is most often created using clay pellets

A drainage layer is a bed of mineral material placed at the bottom of the pot. It can consist of gravel, pebbles, clay pellets, or broken bottle shards. Its thickness is approximately 20% of the container's total height.

A drainage layer is often added when repotting a plant. But it's also possible to install one in the ground.

In the garden or vegetable patch, the use of a drainage layer is almost universally accepted. It loosens the soil and prevents it from retaining too much water. But for potted plants, both indoors and outdoors, the topic is a matter of debate.

The Four Benefits of a Drainage Layer When Repotting

Whether you're a beginner or an experienced gardener, a drainage layer has its uses – Photo by Valérie Goncharuk / Envato

The first argument from advocates of a drainage layer: it keeps the substrate in the pot. In fact, when you repot a plant, you should always use a pot with drainage holes. If you don't put anything at the bottom, the potting mix will drain out through the holes along with the water. A few centimeters of clay pellets help keep the soil inside.

Another argument in favor of the drainage layer: it allows youto adjust the pot size. If you have a pot that's a bit too large or are repotting a variety with shallow roots, such sedum makinoi, you can reduce its depth by adding pebbles to the bottom. Your plant won't be lost in a container that's too large (which is likely to stay damp), and you won't have to buy a new pot.

Proponents of the drainage layer mainly cite another, far more convincing reason: clay pellets and other types of gravel promote water drainage. During and after watering, excess water drains out through the holes at the bottom of the pot. But it also soaks into the substrate. If the substrate remains waterlogged for too long, the roots and your plant are at risk of rotting. When you create a drainage layer, it traps excess water. The soil therefore remains moist but not waterlogged.

Finally, the drainage layer prevents water that pools in the saucer from seeping back into the soil through capillary action. Here again, the mineral material absorbs the liquid. It acts as a barrier and prevents the roots from sitting in water.

Three reasons why you should skip the drainage layer

Clay pellets could hinder root growth – Photo by Beeblebrox / Wikipedia

But this argument is far from convincing everyone. Some plant enthusiasts prefer to do without a drainage layer at the bottom of their pots. To them, it serves no purpose. Worse, they believe it hinders the health and proper care of our plants.

Why? First of all, because the drainage layer limits the available space in the pot. A few centimeters of clay pellets or gravel means that much less space for the potting mix and roots.

Second, a drainage layer is incompatible with bottom watering. The mineral material prevents water from rising into the pot through capillary action. You must therefore water from the top. While this technique works for all plants, it isn't to every gardener's liking. Some swear by soaking the soil, which they claim prevents overwatering and boosts root growth.

To convince us to abandon clay pellets, opponents of the drainage layer have a compelling argument. By trapping water, the mineral material creates a moist environment at the substrate level. The water eventually rises through capillary action and spreads throughout the potting mix. This would keep the potting mix constantly wet, leading to root rot and the death of the plant.

So, what should we do?

Wetting is one of the factors to consider before making a decision – Photo by Anna Nekrashevich / Pexels

The drainage layer isn't like the cream in carbonara pasta. You can do whatever you want and adapt your method based on the plants and your habits.

For starters, skip the drainage layer when watering from below. You can also skip it for potted epiphytes, such as neoregelia carolinae or the hybrid Phalaenopsis. Their substrate contains lightweight materials that retain very little water, so a drainage layer isn't necessary. The same goes for cacti and succulents. Their well-draining substrate theoretically prevents water retention.

Finally, you can skip the drainage layer for mini plants. In a small pot, the potting mix dries out faster, and there's little risk of drowning the roots.

For other species, it's up to you. Do you follow the Monstera app's watering reminders to the letter and always water just the right amount? Then you can skip the drainage layer. If the holes in the bottom of the pot are too large and let the potting mix escape, use a pebble or drainage felt to prevent the soil from falling out.

On the other hand, if you tend to overwater, it's best to keep the drainage layer.

You should also keep a drainage layer if you don't empty the standing water from the saucer or planter. Would you like to skip the clay pellets, but is your Fiddle-leaf fig pot too big to empty the saucer every time you water? Put them in the saucer. They'll absorb the excess water and save your roots. As an added bonus, this trick improves humidity more effectively than misting.