Gardening: do I need a drainage layer?

Some people have been arguing for 25 years about whether Jack had room to ride the plank, or whether Ross and Rachel were really separated. At Monstera, it's a different matter altogether: should you do a drainage layer when repotting your plants? We've compiled the arguments of both advocates and opponents of clay balls at the bottom of the pot, so you can make up your own mind.

The drainage layer is a bed of mineral material placed at the bottom of the pot. It can be made up of gravel, pebbles, clay balls or bottle shards. Its thickness is approximately 20% of the total height of the container.

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

In the garden or kitchen garden, the use of a drainage layer is (almost) unanimously approved. It makes the soil less compact and prevents it from retaining too much water. But when it comes to potted plants, whether indoors or out, the subject is a matter of debate.

The first argument put forward by drainage layer advocates is that it retains the substrate in the pot. In fact, when you repot a plant, you should always use a pot with holes in it. If you don't put anything at the bottom, the potting soil will drain out through the holes, along with the water. A few centimetres of clay balls help to keep the soil inside.

Another argument in favor of the drainage layer: it allows you toadapt the size of the pot. If you have a slightly large pot or are repotting a variety with shallow roots, such as sedum makinoi, you can reduce its depth by adding pebbles to the bottom. This way, your plant won't be lost in an oversized container (which is likely to remain damp), and you won't have to buy a new pot.

Advocates of the drainage layer advance another, far more convincing reason: clay balls and other gravels help water to drain away. During and after watering, excess water drains away through the holes at the bottom of the pot. But it also soaks the substrate. If the substrate remains soggy for too long, the roots and your plant risk rotting. When you make a drainage layer, it retains excess water. So the soil remains moist, but not waterlogged.

Finally, the drainage layer prevents the water stagnating in the saucer from rising up into the soil by capillary action. Here too, the mineral material absorbs the liquid. It forms a protective layer and prevents the roots from soaking in water.

But this demonstration is far from convincing everyone. Some plant-addicts prefer to do without a drainage layer at the bottom of their pots. For them, it's useless. Worse still, it's detrimental to the health and maintenance of our plants.

Why would this be? Firstly, because the drainage layer limits the space available in the pot. A few centimetres of clay balls or gravel means a lot of space that potting soil and roots can't occupy.

Secondly, the drainage layer is incompatible with watering from below. The mineral material prevents water from rising up into the pot by capillary action. You must therefore water from above. While this technique is suitable for all plants, it's not to everyone's taste. Some swear by basins, which prevent over-watering and boost root growth.

To convince us to abandon clay balls, the anti-drainage layer have a shocking argument. By capturing water, mineral matter creates a humid environment in the substrate. The water eventually rises by capillary action and diffuses into the soil. The latter would remain constantly wet, leading to root rot and plant death.

The drainage layer is not like the cream in pasta carbonara. You can do as you please and adapt your method to suit your plants and your habits.

For starters, forget the drainage layer when watering from below. You can also forget about it for potted epiphytic plants such as neoregelia carolinae or phalaenopsis hybrid. Their substrates contain light materials that retain little water, and a drainage layer is not necessary. The same applies to cacti and succulents. Their draining soil theoretically prevents water retention.

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

For other species, it's up to you. If you follow the watering reminders on the Monstera app to the letter and always water just enough,you can skip the drainage layer. If the holes at the bottom of the pot are too big and allow the soil to escape, use a pebble or drainage felt to prevent the soil from escaping.

On the other hand, if you have a heavy hand when watering, it's best to keep the drainage layer.

It's also a good idea to keep a drainage layer if you're not emptying the water that stagnates in the saucer or planter. You'd like to dispense with the clay balls, but your Lyre fig 's pot is too big to empty the dish every time you water it? Put them in the saucer. They'll absorb the excess water and your roots will be saved. The icing on the cake is that this trick improves hygrometry more effectively than misting.