Introduction
It’s Saturday morning, after a busy week at work you are craving a little ‘green’ time. It’s the perfect day for an indoor gardening activity – repotting some of your indoor plants. Simple, right?
But, upon walking down the indoor gardening aisle at your local hardware store or garden centre, it quickly becomes obvious that there is a massive range of indoor potting soils to choose from.
So many packages, so many options and they range in price and quality so how do you know what is the best potting soil for indoor plants and specifically the right soil for your indoor plants?
Confused?
Well good news, if you read on, we have put together all of the essential facts, information and advice you need, including:
- What is the difference between soil and potting mix?
- What makes the best soil for indoor plants?
- How to choose the best soil for indoor plants?
- Plants with specific needs – succulents, cacti, african violets and orchids.
- What is the best potting soil for indoor plants?
- Recommendations on the best soil for indoor plants.
- How to maintain plant and soil health?
This article provides a complete guide to everything you need to know about selecting and using the best soil for indoor plants.
If you want to jump to a specific topic, please use the table of contents on the right of your screen.
What is the difference between soil, potting soil and potting mix?
Over the years, I have slowly killed more indoor plants than I would like to admit and in doing so I have also learned a lot about what not to do….. and digging up soil from my garden to use in pots for indoor plants is one of those lessons!
Indoor plants need a quality growing medium offering a combination of drainage, water retention, aeration, nutrients and soil pH for them to grow and thrive.
Potting mix, potting soil, soil, growing medium, miracle soil, are all words used to describe a medium in which to grow indoor plants in pots or containers.
1: Potting soil is not soil at all.
Despite their names, in reality little or no soil is used in potting soil because it is considered too heavy for growing indoor plants. Instead, most commercially available potting soils are built upon a base of either peat moss or coconut coir.
Don’t worry about getting all caught up in these differences – someone else has done the hard research. Just understand that potting soil contains additional ingredients used in the mix to improve drainage, to increase water retention, and to feed your indoor plants.
So why don’t we just use soil from the garden? Well, the average garden soil can contain bugs, fungus, bacteria and even seeds that you don’t want to being into your home.
It is also very heavy and generally quite dense. The density can lead to root rot from retaining too much moisture or can lead to stifled root growth.
So, simply put, soil from your garden is considered too heavy, may contain bad stuff and lacks some of the necessary components that make a good quality soil for your indoor plants.
So, now you know the difference! But to avoid any confusion in our article we will use the terms potting soil and soil to refer to commercially available potting mixes for indoor plants.
Why is using the best soil for indoor plants so important?
Your potting soil is one of the most important factors in maintaining the overall health of your indoor plants.
Depending on the varying needs of your indoor plants, your potting soil will also need to vary in drainage, consistency, and moisture retention qualities.
Contrary to popular belief, potting soil is not just a bag of dirt. Commercially available potting soils are the result of hours and hours of research, product development, experimentation and manufacturing to ensure that your indoor plants get the support and nutrients for optimal growth.
Using the best soil for indoor plants ensures that you are providing the best foundation for your indoor plants to grow, thrive and be healthy.
What are the key qualities of the best soil for indoor plants?
2: Regardless of the brand, all commercially available potting soils are designed to address four common elements vital to the health of all indoor plants.
Even though the mix of ingredients in commercial potting soils will differ from brand to brand, there are a number of common elements that are vital to the health of all indoor plants:
- Moisture retention – The potting soil must hold the right amount of moisture to nourish the plant in between watering.
- Aeration – The potting soil must allow space for the roots to breathe and for excess water to drain away.
- Nutrients – The potting soil must contain enough nutrients for the plant to live and grow.
- Anchoring – The potting soil must have enough structure to support the root system of your indoor plant.
So, we have learned about the common elements – moisture retention, aeration, nutrients and anchoring – but what ingredients are used to change the properties of the potting soil. Let’s explore this a little further.
Drainage and Moisture Retention
If you are thinking about the best soil for indoor plants and the optimum environment for your indoor plants, then you should be thinking about their drainage and moisture requirements.
Some plants need more moisture in the soil than others.
Let’s think about some plants and the environments that they originated from:
- Tropical plants originated in jungles and tropical environments. They thrive in a moist environment and need a soil that retains moisture.
- Succulents and cacti originated in dry, desert-like environments. So, the best potting soil for succulents and cacti would be a sandy potting soil that does not hold moisture.
There are also other indoor plants that have very specific potting soil needs such as African Violets and Orchids.
And, the majority of plants do not like to sit in soggy, waterlogged soils. This leads to root rot – so drainage is extremely important.
What is used to change the drainage and moisture retention properties of potting soils for indoor plants?
Perlite and vermiculite are used to change the drainage and moisture retention properties of potting soils for indoor plants.
Perlite is a lightweight volcanic glass mixed into potting soils that improves water retention, aeration and drainage. If you roll it between your fingers, it feels a little bit like Styrofoam.
Perlite is best for keeping soil loose, that is creating gaps in the potting soil for air, water and drainage.
These gaps allow for aeration but also ensure that water and nutrients can easily travel through the potting soil to the roots of your indoor plant. We want any excess water to travel out of the pot so the potting soil does not get soggy and perlite assists with this.
Vermiculite is, in principle, the opposite of perlite.
Vermiculite is comprised of absorbent, sponge-like flakes mixed into potting soils. It helps improve potting soils by retaining some water and draining any excess water.
In reality, unless you are thinking of making your own potting soil (a whole topic in its own right!), you don’t need to study up on perlite and vermiculite.
Just understand they are likely to be components, to a greater or lesser extent, of the best potting soil for indoor plants.
Soil pH
So far, we have concerned ourselves with the texture and properties of potting soil. But there is another aspect that some indoor gardeners may be interested in.
For the everyday indoor gardener, soil pH is not something you will need to study. However, some plants are a little fussy about the soil pH so you might want to understand the basics.
The soil pH tells us the acidity or alkalinity of the potting soil. The pH scale runs from 0 to 14, with 7.0 being neutral.
Measurements between 0 and 6.9 are acidic soils, and those between 7.1 and 14.0 are alkaline soils.
Most commercially available potting soils for indoor plants have a pH of 7.0, which is perfect for the majority of indoor plants. Phew, we don’t need to worry!
However, if you are considering growing indoor vegetables, soil pH is something you should consider reading up on in more detail.
How to choose the best soil for indoor plants?
So, you are an expert, or at least more informed, about the essential properties of potting soils. But now that you are in the garden center or hardware store, how do you make sure you are getting the absolute best soil for indoor plants:
- Be fussy and purchase the best potting soil for indoor plants that you can afford. Cheap potting soils can end up being very expensive if everything you plant in the soil dies.
- Check the packaging. The packaging should be fully sealed and in good condition. If you see any holes in the packaging, there is the potential for bugs, fungus and parasites to have worked their way in. If the packaging is faded or showing signs of weather damage, the contents and nutrients might have already started to break down. If you see any small insects flying around the packages, the potting soil might contain fungus gnats.
- Pick up the bag and feel the contents. The potting soil should be loose and fluffy, not in one lump.
- Check if the potting soil contains fertilizer. Some commercially available potting soils contain fertilizers, and some don’t. Check the NPK rating of each potting soil. Read our article titled Best Fertilizer for Indoor Plants for more information on what this means and how to read the NPK rating. I like using a potting soil that does not contain fertilizers. That way, I can control the fertilization of my indoor plants with indoor plant fertilizers. Either way, just know what you are getting so you don’t over or under fertilize your indoor plants.
- Don’t purchase potting soils with water retention gels or crystals included. While these might cut down the frequency of waterings, they can’t be relied upon and just complicate indoor plant care.
What is the best potting soil for indoor plants?
If you plant your indoor plant in the wrong type of potting soil, it will not be happy and you will see signs of growth problems, decay, and perhaps even root rot. If you find yourself frequently fertilizing your indoor plants to keep them healthy and alive, they are probably in the wrong type of potting soil. That is, the soil is not supporting their health and growth.
When you buy a plant from a garden center, they usually come with a plastic tag with plant-care instructions. Get to know your plant by reading this information.
Alternatively, you can research the needs of your indoor plant in plant care books. The internet is also a great resource for researching your indoor plant needs.
Armed with this information, you can choose the best soil for your indoor plant. We have a few recommendations below:
Best all-purpose potting soil
Are there different potting soils for different plants?
With close to 500,000 different plant species, originating from an extraordinary range of climates and soils, it is important to recognise this diversity when growing indoor plants.
Commercially available potting soils are usually formulated to mimic, as closely as possible, the soil conditions that indoor plants naturally prefer.
3: Some indoor plants need specially formulated potting soils to address their needs.
There is a vast range of all-purpose indoor potting soils, but there are still some types of indoor plants for which you should consider specially formulated blends – African Violets, succulents, cacti and orchids.
Take the time to explore the various commercially available potting soils to see which indoor plants and conditions they are designed for.
When you match the potting soil to the needs of your indoor plants, they will thrive and reward you with glossy growth and fresh air.
What is the best soil for cactus and succulents?
Cacti and succulents are generally, not always, found in dry, arid, desert-like environments. The soil in these environments is very sandy or gravelly with little organic material in it. On the rare occasions that it does rain, water soaks in and quickly disappears deep into the soil.
Therefore, the best potting soil for indoor cactus and succulents should have a high percentage of coarse sand or grit, allow any excess water to drain away quickly and be relatively nutrient-deficient.
Best soil for cactus and succulents
We recommend this commercially available potting soil designed for cactus and succulents:
What is the best soil for indoor African Violets?
African Violets also have special needs including a potting soil low in nitrogen and high in potassium with added calcium to encourage continuous flowering.
Best soil for African Violets
We recommend these commercially available potting soils designed for African Violets:
What is the best soil for indoor orchids?
Orchids have special needs and require a different type of potting soil to typical indoor plants. This is because orchids are epiphytes aka ‘air plants’ and live on the surface of other plants, trees, and even rocks.
If you plant an indoor orchid in an all-purpose potting soil, the orchid will suffocate. This is because the soil cannot provide the required airflow to the roots for the plant to survive and grow.
Best soil for orchids
We recommend these commercially available potting mixes specifically designed for orchids:
What if I have used the wrong potting soil?
In most cases, using the wrong potting soil probably won’t have a devastating impact – especially if you have purchased a general all-purpose potting soil. However, if you pot a cactus into an all-purpose potting soil, it will struggle to survive and grow because the potting soil will retain too much moisture.
Usually, the best way to solve these problems is to replace the potting soil with one that has been specifically formulated for your indoor plant.
How do I maintain soil health?
All potting soils decompose, and when they do this will affect your plants:
- Potting soil slowly breaks down and compresses. In the pot, it will look like the soil is disappearing or settling. As this happens, there is less and less room for air gaps around the roots of your plant. Essentially your indoor plant will suffocate.
- Drainage is obstructed. Soil particles become smaller and smaller making it harder and harder for water to travel to the roots of your plant and to drain out of the pot.
- Salt and other minerals build-up. As the drainage becomes obstructed, this situation allows for a faster build-up of salts from fertilizers and minerals from tap water. This stresses your indoor plant and can lead to all sorts of health issues.
The best and simplest way to maintain soil health, is to inspect your indoor plant’s soil frequently and repot every 12 – 18 months
How do I maintain my indoor plant health?
Take these steps to ensure your plants have the soil they need:
- Repot every 12 – 18 months. Although commercially available potting soils are structured to provide your plant with an optimum growing environment, sooner or later the potting soil ingredients start to break down and settle. When this occurs, the potting soil absorbs water less efficiently, requires more frequent fertilization and can suffocate the roots. Repotting every 12 – 18 months ensures your indoor plants remain healthy and have room to grow.
4: Regardless of the type of potting soil you use, you will need to repot your indoor plants every 12 – 18 months.
Read our article titled Indoor Gardening 101: How to Plant Indoor Plants Like a Pro for more information about potting and repotting.
You might want to watch this excellent YouTube video called How to Replant Houseplants – Quick Version as well.
- Drench the soil thoroughly every month. Place your indoor plant in the kitchen sink, bath or even your shower. Gently but thoroughly flush the soil to wash out accumulated salts from fertilizer and mineral deposits from tap water. Read our article titled Best Fertilizer for Indoor Plants for more information on watering and drenching.
- Remove excess water after watering. Using a tray under your indoor plants is an excellent way to protect against water damage to your floors, rugs and carpet. But if water collects and remains in the tray for an extended period of time, root rot can set in. Empty your indoor plant trays after each watering. Read our article titled How to Water Indoor Plants Like an Expert for more information on watering.
- Fertilize and inspect your indoor plants regularly. Read our articles titled Best Fertilizer for Indoor Plants and Getting Rid of Indoor Plant Bugs for more information.
Final thoughts
In most instances, the answer to the question, what is the best potting soil for indoor plants, is an all-purpose commercially available potting soil. These potting soils are formulated to meet the needs of most indoor plants and provide the right moisture retention, aeration, and anchoring qualities.
As indoor gardeners, we demand a great deal out of potting soils expecting them to support and nourish our indoor plants, often for years at a time.
Selecting and using the best soil for indoor plants is such a crucial first step.
When you match the potting soil to the needs of your indoor plants, they will not only thrive but also reward you with glossy foliage and fresh air.
Make sure you hang around and check out our other indoor gardening blog posts.
Remember, life is better with indoor plants!
