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Why is good soil drainage so important for houseplants? | how to make a good potting mix

Having a houseplant in a well draining soil is crucial for its roots health. As compact, constantly wet soil is actually killing your plant, it’s important to understand why and how to achieve a well draining soil. In that way we can help our plant maintain healthy roots and watch it thrive for many years to come.

To understand what type of soil mix is optimal for our houseplants, first we need to understand what roots need.

Besides water, plant roots actually need oxygen, too.

Oxygen plays a crucial part in overall root health and without it, roots start to rot. Depending on the plant, that can happen practically overnight (in case of some succulents, for example) or it can develop more slowly through time.

Now that we know that roots need water and oxygen, the next thing we need to find is the right balance between these two.

Too much water (or better said – constantly wet soil) will cause root rot.

On the other hand, if there’s too much oxygen (soil too dry) around the roots, they’ll stop functioning.

You can see now why it’s important to find a good balance, so that the roots get as much water as needed, but oxygen too. But you don’t need to worry, it sounds more complicated than it actually is. To achieve that is fairly easy. We need two things:

  1. a pot with drainage holes
  2. good soil mix

Pot with drainage holes

Having your houseplant potted in a pot with drainage holes on the bottom is extra important.

There are people who, for what ever reason, encourage otherwise. And, as it’s possible to work without drainage holes, that’s far from optimal and just an additional hassle we need to worry about while watering.

Having your houseplant potted in a pot WITH drainage holes allows us to give our plants a thorough watering (so that water reaches all parts of the root system) while at the same time letting the excess water to drain out.

If there weren’t drainage holes, all the excess water would stay on the bottom of the pot. This would overtime cause roots to – literally – suffocate and begin to rot.

There are several “types” of overwatering situations.

The first one is if you keep constantly watering your plant, without letting the soil even just slightly dry out between watering (depending on the type of plant and its needs).

The second is when water retains on the bottom of the pot without drainage holes. In this case, even if we let the soil dry for the first few inches, there is a 99% the soil is still quite moist, or even wet, on the bottom.

Finally, the third is the case of poor soil that takes ages to dry out. You may water your plant and check on it once a week, and find that even after 3 weeks for example, the surface of the soil did not begin to dry what so ever.

Which brings me to…

Good soil mix for houseplants – how to make it yourself

Besides drainage holes, a good, well draining soil mix is crucial for root health. So how do we make it?

Good soil mix for houseplants consists of three things:

  1. material that retains moisture (holds water) – like peat, coco coir and clay
  2. material that allows water to drain + introduces oxygen (aeration materials) – like perlite, LECA, zeolite, pumice etc.
  3. hummus – to give our plants some nutrients

To achieve good drainage, we need to mix together something that will retain water and at the same time something that will allow air circulation throughout the pot.

When we water our plant, water pushes out all the air from the soil. So when we add some of these aeration materials to regular soil, they not only allow better water drainage, but because of their hollow structure that is filled with oxygen, they literally bring oxygen into the soil, too.

Aeration materials… which one is the best?

Besides “clean” peat or coco coir, you can also buy a regular potting mix for houseplants. That mix will probably have some perlite mixed in it already, but in most cases it won’t be enough. So I encourage you to buy some additional perlite or pumice or what ever aeration medium you want to use.

Depending on the plant and its requirements you can choose different types of aeration materials.

There are some that have better capacity to absorb and retain water (perlite, vermiculite, zeolite, pumice), while others don’t (LECA).

The winner in absorbing and holding water is definitively vermiculite, so it’s a good choice for plants that like their soil more on the moist side, like prayer plants (Calathea, Maranta, Stromanthe, Ctenanthe).

There are also some that are able to absorb and retain nutrients we add to soil while we fertilize our plant (vermiculite, zeolite), while others have a very low capacity to do that (LECA, perlite, pumice).

Most commonly used are:

  • perlite
  • LECA (clay) pebbles
  • pumice
  • vermiculite
  • zeolite

To achieve good drainage, all you need to do is mix, in volume, 70-80% soil (peat, coco coir) with 20-30% of some of these aeration materials.

The ratio between these materials will vary depending on the plant and its watering needs.

For example, a plant that likes its soil to dry out fairy quickly, will need more aeration material (30% of the soil mix), while plants that like having soil more on the moist side, will need less (about 20%).

As you see, it’s not difficult to improve drainage for your houseplants. Just by adding some extra aeration materials will help them and help you, too. You won’t need to worry so much about overwatering and having your plant in soil that takes ages to dry out.