Houseplants & Potting Mix 101: A Guide to Understanding Potting Mix for New Plant Parents

I recently discussed the 4 non-negotiables in houseplant care or the 4 essential elements we have to provide our plants with to keep them happy and thriving. (linked to the original post)

The 4 non-negotiables are light, air, water, and nutrients.

Today’s post is going to focus on how to provide enough air for a plant at the root level, which means focusing on how to ensure the potting mix a plant is in provides enough aeration for the roots to stay healthy.

We will cover:

  • Why plants need air, even at the root level
  • What happens if the roots lack air
  • How to provide the aeration your plant needs
  • & Whether it is possible to provide too much air

Table of Contents

Plant roots need air in addition to water and nutrients

Roots breathe in the air kind of like we do. They use oxygen in a process called respiration.

Respiration uses food (glucose) and oxygen to create energy for the plant to grow.

If you want to know more about respiration, click here to expand

Respiration is the process of combining glucose and oxygen to create energy, carbon dioxide, and water.

The energy created is used by the plant to live and grow.

Carbon dioxide and water are waste products or leftovers from the process that get released into the environment.

Photosynthesis and respiration are both essential for the plant to live.

Photosynthesis creates the glucose (or food) used during respiration.

Photosynthesis also produces a waste product, oxygen, which is released into the environment for other living things to use (including us!).

So, in other words, the plant needs to absorb light energy to fuel Photosynthesis so it can create glucose.

Then, it uses respiration to combine oxygen with glucose/food (from photosynthesis) to nourish and energize itself for growth and vitality.

All parts of a plant absorb oxygen for this purpose: leaves, roots, shoots, etcetera.

Roots also need to absorb moisture and nutrients, which people are usually more aware of because that is why plants need to be watered and fertilized.

Where do roots get the air they need?

Plant roots absorb air that exists in the small spaces between soil particles.

When plants grow in the ground, worms and other creatures live in the soil. These creatures aerate the soil by moving it around and loosening it up. They also create waste that provides nutrients for the plant and replenishes the soil.

In our homes, houseplants do not have all of these little workers helping plant roots maintain healthy soil with air pockets, movement, and nutrients.

So indoors, we need to build in a system that maintains these air pockets for our plant’s roots.

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What happens when roots lack oxygen?

Roots can suffocate and begin to die.

The stagnant conditions of the potting mix combined with dying roots allow bad bacteria and fungus to prosper.

The bad bacteria and fungus start to rot away the dying roots causing toxic conditions which result in more root death and eventually plant death.

How do you ensure your potting mix is providing the plant with enough oxygen?

To add air pockets to your potting mix, you can add lots of different natural materials that are light, airy, and break up the dense soil.

The most popular soil additives are perlite, pumice, and orchid bark, but there are many to choose from. Some are included in the list below.

What ratio of dense potting mix to aerating materials should you use?

Most houseplants can do quite well in either a mix of two-thirds indoor potting mix to one-third aerating materials like perlite, pumice, etcetera. But this is just a starting place as people use all kinds of combinations successfully.

If you are an overwaterer, like me, you could try 50% indoor potting mix to 50% perlite, pumice, or other aerating materials.

If you are an underwaterer, you could add less than a third of aerating substrate. But, be careful not to have too little aeration.

I’ve created a list of some common substrates people use to add aeration to a mix. Many of these will be available in your local greenhouse supply store.

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Can you add too much aeration to a potting mix?

Yes! It is possible to make the potting mix so well-draining or so well-aerated that the plant isn’t able to get the moisture it needs when you water the plant. The mix dries too quickly and the plant is super thirsty again.

The result of adding too much aeration is accidental underwatering, which can be just as harmful to a plant as overwatering.

If the roots stay dry for too long, the ends of roots may begin to crisp and die back. Then, when you water, the dead parts of the roots begin to rot.

Why? Dead matter plus water equals the perfect breeding ground for fungal and bacterial blooms, who feed off of dead decaying stuff and moist conditions.

How do you know if your plant isn’t getting enough water?

If lower leaves are turning yellow then crisping up and falling off, you might be underwatering.

If the plant droops frequently, you might be underwatering.

If the plant is looking dull and sickly, you might be underwatering.

To remedy the issue, you can either try repotting the plant into a mix that will hold a little more water and removing any dead roots or try checking the plant to see if it is dry daily to see how often it needs to be watered in its current potting mix.

Big Takeaways:

  • Roots need oxygen just as the rest of the plant does
  • Roots get oxygen in the wild from the air pockets in the soil, created when creatures move the soil around
  • Indoors we do not have creatures turning the soil over, so we must add something to the dense soil to create pockets of aeration for the plant
  • The most popular additives are perlite, pumice, and orchid bark
  • Finding out how much to add is a personal journey because everyone’s homes, plants, and environments are different. However, a good place to start is 2/3 potting mix to 1/3 aerating material



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