DIY Potting Soil Mix for Indoor and Container Plants

best soil for indoor plants

For years, I thought I was terrible at keeping indoor plants alive. Forget a green thumb, my thumb apparently was great at killing plants and not so great at keeping them happy. I could keep my outdoor garden alive no problem but I couldn’t figure out why I struggled so much with indoor plants!

Lack of green thumb or not, I also have this obsession with building plant walls, so I had to figure out how to keep my living decorations from a slow and certain death. In short, after many struggles, I found the key and it was easier than I thought!

If this post was a Friends episode, it would be “The One Where I Stopped Murdering Plants.” 🙂

It’s All About That Base (Soil)

A trip to the library, conversations with a master gardener, and an exhaustive web search led me to realize that I was only part of the problem. I certainly did need to get better about knowing when and how much to water, but I also needed to find better soil.

Turns out the reason I had so much success with outdoor plants was the same reason my indoor plants struggled: the soil.

Now that I know, the solution is so logical! Indoor and outdoor plants have much different requirements for what we plant them in!

My outdoor garden was thriving with an abundance of homemade compost and companion planting to keep plants strong. My poor indoor plants, on the other hand, only had the soil in their pot to live on. And it turns out that quality of soil (even organic potting soil) can vary greatly and nutrients need to be replenished regularly.

Understanding that opened the door to a world of research about dirt vs. soil vs. potting mix. And it led to much happier plants! If you’ve killed more than your fair share of innocent houseplants like I have, read on for a solution!

Potting Soil vs. Potting Mix

My master gardener friend set me straight right away. Potting soil and potting mix are not the same thing.

Confusing, right?

But there is a big difference and this is the distinction:

  • Potting Mix: High quality potting mix usually does not contain actual soil or dirt. Usually a mixture of peat, organic materials, and some type of nutrient mix, these are often confused with potting soil because they are a medium that plants grow in.
  • Potting Soil: Can vary widely based on brand. It may actually just be soil. Some contain fertilizer but at levels that can harm young plants. Others don’t contain enough nutrients and can starve plants (what I was doing).

In short, my rookie mistake was buying an organic potting soil and thinking my plants had everything they needed. They didn’t.

Realistically, the two terms can be used interchangeably and I’m splitting hairs. The important lesson is that whatever you plant your indoor plants in, it needs to have certain key factors for plants to thrive.

What Container Plants Need

More than just soil, apparently!

To thrive, indoor and container plants need to be planted in a mixture with a few important qualities:

  1. Drainage– Plants need a container and potting mix that allows excess water to drain off easily.
  2. Holds water- Yet they also need the potting medium to hold on to enough water that they don’t get parched.
  3. Won’t compact quickly– The mixture should also be fluffy and light so that it won’t compact too quickly and plants can easily spread roots.
  4. Provides nutrients– And the mixture should have enough of the right kind of nutrients to start out so the plants can flourish.

How to Make Potting Soil

If you’ve been around here much, it probably won’t come as a shock to you that all of this research led me to the conclusion that I needed to make my own dirt. (Or potting mixture… told you those terms could be easily confused).

The DIY aspect isn’t too surprising since I’m already the type to make my own toothpaste and build a coffee bar on a whim. But dirt was a new venture for me and my hubby thought it was a tad bizarre when I started mixing a gigantic bowl of dirt in the garage. But I digress.

But First, Safety

I’m not the overprotective type. I encourage my kids to run around barefoot and climb trees. I don’t think everything is out to get us, but there are a few important safety precautions to follow when dealing with potting mix ingredients.

Legionnaires’ disease, a severe form of pneumonia, is rare but can be contracted from a type of bacteria that can live in soil, compost, and potting mix ingredients. It’s contracted by breathing in the bacteria in the air so it’s worth wearing a particulate face mask and gloves when mixing your own potting mix. Wash hands and clothing well after mixing and try not to mix dry ingredients in a windy area.

Now that we know how to safely play in the dirt… on to the recipe.

Potting Mix Ingredients

This recipe is for a general purpose potting mix. Different plants have different requirements for their potting mixture so do a quick search for your specific type of plants and tweak as needed. A good multi-purpose mix contains:

  • Organic Coco Coir Peat– A sustainable and natural fiber made from the outer shell of coconuts. It is a byproduct of the coconut industry and is eco-friendly. Peat helps keep the soil retain water and stay light and fluffy.
  • Organic Vermiculite– Technically a hydrous phyllosilicate mineral, or volcanic mineral that expands when heated. Vermiculite helps loosen the soil, prevent compaction and encourage root growth.
  • Organic Compost– A high quality homemade compost or organic pre-made gives the mixture nutrients to feed the plants. Just be careful as some types of compost that are not thoroughly broken down can burn young plants and be too harsh for container plants.
  • Organic Worm Castings– Don’t let the fancy name fool you… this is essentially worm poop. It’s also an amazing natural fertilizer created when worms work through the soil. This adds nutrients to the mixture.
  • Sand- Optional but also good for drainage.
  • Organic Garden Lime – Soil pH affects house plants and lime may be needed to alkalize to the correct level.
  • Organic Soil Acidifier– If the soil is too alkaline, a sulfur base acidifier can help achieve the correct pH.

Mixing the Potting Soil

This part is easy!

You’ll just need your safety gear and a big enough container to mix enough for whatever you need to plant. I’ve listed the recipe in “parts” so you can easily adjust to whatever amount you need. If you need a small amount, a “part” might be just one or two cups. For big projects, a “part” might be a gallon, a bucket, or any other large container.

I used this formula to make my own potting soil:

  • Start with 1 part rehydrated coco coir (instructions below), 1 part vermiculite, 2 parts compost;
  • Then add 1 cup of sand and 2 TBSP worm castings per gallon of finished potting mix;
  • Finally, measure and balance the pH with lime and sulfur.

Here’s exactly how I did it:

Step 1: Rehydrate the Coir

The ratio of water to rehydrate coco coir is 8:1 by weight. This means that a pound of coir needs 8 pounds of water (about a gallon) to rehydrate, and 10 pounds would need about 10 gallons. Warm water speeds up the process (but don’t heat water over about 110 degrees).

Coco coir makes up about a quarter of your finished mixture by volume so depending on how much you make, you may not need to hydrate the entire block.

In a large container, pour the warm water over the coir and let hydrate. It may take a couple of hours to fully hydrate. As it hydrates, it will become easy to break apart. It’s ready to use when it is easy to crumble and is a consistently light, airy, and moist throughout.

Step 2: Add Vermiculite

Use equal parts of coir and vermiculite and this will make up about half of your finished mixture.

In a large container, mix the rehydrated coco coir with an equal amount of vermiculite and stir to combine.

Step 3: Add Compost

You’re half way there! You’ve made about half of the mixture by volume. If you have two gallons of combined coco coir + vermiculite, you’ll end up with just over four gallons of finished potting mix and so on.

Whatever measure you’ve used as a “part,” you’ll now add two of this measure of compost. Or if it is easier, add compost to equal the amount of coco coir + vermiculite you just mixed.

Stir well by hand to combine.

Step 4: Add Sand and Worm Castings

For every gallon of mixture, you’ll now add 1 cup of sand and 2 tablespoons worm castings. Mix well to combine and until the mixture is an even consistency.

Step 5: Check and Adjust pH

Now for a little chemistry!

Your potting mix is almost there but it’s time to double check the pH. It’s important to test and get this step right. An incorrect pH can also kill a plant pretty quickly (and I’m sure I accidentally killed a few this way too!).

I use a 3-in-1 meter to make sure I have pH correct. As a bonus, it also checks moisture in the soil so you can use it to know when you need to water your plants as well! In general, plants need a pH between 6-7 (slightly acidic to neutral).

Depending on the compost you used, the pH may be too low. In this case, add small amounts of lime until you reach the desired pH. If the pH is over 7, you’ll need to use a soil acidifier to bring it back down. This chart shows the desired pH for many common plants. I aim for 6.5 for all indoor plants.

To make sure I have the pH correct, I mix a few days before I need it and re-check the pH over several days, adjusting as needed.

How to Store Extra Potting Soil

I know, I know… it isn’t actually soil. It just sounds better than saying potting mix over and over!

If you have any extra, store in an airtight container until you need it.

Maintaining Potting Soil Mix Quality

One last very important step!

You’ve just created a great potting mix that should last for a while, maybe even a year or more. But, your plant will use up the nutrients in that soil and need food over time. This was another big mistake I kept making. I was giving my plants “soil” at first and expecting them to have enough nutrients to live forever.

Now, I add an organic fertilizer diluted in water every couple of weeks when I water the plants. My plants seem much happier now that they aren’t starving to death!

When to Change the Potting Soil Mix

Even with the best soil, potted plants can’t live forever. My master gardener friend recommends re-potting plants each year for best results. I know, this seems like a lot of work, but the plants will likely need a bigger pot by that point anyway, and this helps ensure that your plants stay happy and keep growing.

When Not to Make Potting Mix

If you also suffer from PWCD (plant wall creation disorder, self diagnosed) as I do, you’ll likely need a lot of this stuff. Making your own saves time and money and lets you make sure your plants get what they need.

If you’re just potting one or two plants for your house, you probably don’t need to make your own. Instead, just look for a high quality potting mix (not just soil), check the pH as mentioned above and add fertilizer as needed.

There you have it! Two thousand words all about potting soil mix. Hopefully this helps you keep your plants alive like it has helped me.

Your turn… do you have houseplants? Share your best tips for keeping them happy!

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