Does this sound familiar? You take loving care of your houseplants. You make sure to water them regularly, provide enough light and maybe even enough humidity.
As a result, your plants are doing quite well, but they are not thriving.
At least, that’s what happened to me. For quite a while, in fact. That was until I got more involved with the subject of substrates.
In this post, I’d like to share my findings and encourage you not to buy just any potting mix but to choose a substrate based on the needs of your houseplants or even mix it yourself. It’s easier than you think!
Properties that all substrates should meet
In addition to the specific needs of different houseplants, there are requirements for the substrate that make it suitable for most houseplants.
- Easy absorption and temporary binding of water
- Sufficient drainage so that roots do not rot
- An airy structure so that the root system can breathe
- Nutrient storage to supply the plant with nutrients
- Maintenance of the structure
- Stable pH between 6.0 and 6.5
Should you use ready-made soils or mix the substrates yourself?
Now that we know what demands we have on a plant soil or substrate, the question arises whether to use a ready-made plant soil or a self-mixed substrate.
This question can not be answered generally with yes or no. It depends a lot on you and your preferences. I have summarized the advantages and disadvantages of the two options so that you can decide for yourself.
In the following, we will investigate the topic and analyze ready-mixed soils. Finally, we will go into individual components of substrates and their properties.
In addition, I will show you an essential mix that you can use for many houseplants. You will also find links to other substrate recipes for specific plant families.
Advantages and disadvantages of ready-made potting mixes
Advantages
- Little effort (no searching and mixing of ingredients)
- Cheaper in small quantities
- Can be purchased in small quantities
- Easy storage
Disadvantages
- Often not individually adapted to the needs of the plant
- Usually too small particle size and therefore not airy and too wet
- Depending on the storage of the seller already contaminated with pests
- Too low perlite content to have a noticeable effect
- With cheap soils, not all components are always readily composted
Advantages and disadvantages of self-mixed substrates
Advantages
- Exactly adaptable to the needs of your houseplant
- Depending on the mixture’s coarse structure for plenty of air around the roots and little moisture accumulation
- Since many components are low in nutrients, they are uninteresting for many pests like fungus gnats
Disadvantages
- Components partly only from 11 lbs acquirable
- More effort for purchasing and mixing
- It takes, depending on how you store it, more place than a bag of premixed earth
A point of the case dependent can be an advantage and disadvantage that finished soils are often pre-fertilized. That saves having to fertilize on your own – at least for some time. In exchange, however, it can also be a downfall when damaged roots try to regenerate.
An overview of ready-made potting mixes
Now that we have an overview of the advantages and disadvantages of ready-made soils and self-mixed substrates, we can delve deeper into ready-made potting mixes.
Here, the market has a lot to offer. From universal soil to bonsai soil, everything is there. The following will take a closer look at the most common grounds.
Universal potting mix
The goal of a universal soil is to fit for as many plant groups as possible. It is advertised that you can use this soil for indoor plants, vegetables, and potted plants. Therefore, it usually contains many nutrients. Its pH can range from 4.8 to 7.5, depending on the supplier.
Due to its many small components, it retains a lot of water and falls rather compactly around the roots. These characteristics, in my opinion, disqualify it for many houseplants.
It usually consists of the following ingredients:
- Shredded compost
- Wood or coconut fibres
- Bark humus
- Various fertilizers
Potting soil
Potting soil is designed to provide flowering plants with everything that will lead to full bloom, and it is often somewhat less nutrient-rich than universal potting soil. Also small in particle size, it retains water similarly well and surrounds the roots with almost no gaps.
Ingredients such as perlite are often added. However, the amounts are usually not sufficient to have a real effect. The pH value is usually around 6.0.
Potting soils are also not suitable for most houseplants, in my opinion.
They consist of the following ingredients:
- Raised bog peat in various stages of decomposition
- Shredded green compost (comparable with garden compost)
- Lime powder
- In small quantities of perlite or clay granules
- Various fertilizers
Green plant and palm tree soil
Green plant and palm soil are probably the soil mixtures that are most suitable for indoor plants. It has a moderate amount of nutrients compared to other soils. Thus, you can use it for plants such as palms with lower nutrient requirements
However, this statement does not apply to one nutrient: nitrogen. It is supposed to provide vigorous leaf growth. The pH value is usually around 6.0.
Like the other soils, green plant soil retains quite a bit of water and falls tightly around the roots.
It often consists of the following:
- Raised bog peat in various stages of decomposition
- Shredded green compost (comparable with garden compost)
- Small amounts of perlite, lava granules, or clay granules
- Small quantities of sand
- Various fertilizers
Succulent and cactus potting mix
Succulent and cactus soil is a rather nutrient-poor soil mixture. These soils often contain sand, which is intended to improve drainage.
A rather fine structure is typical. Due to the sand, it clumps comparatively little.
The pH value is usually around 6.0.
Succulent and cactus soils usually contain the following:
- Raised bog peat in various stages of decomposition
- Sand
- In small quantities of perlite, lava granules, or clay granules
- Different fertilizers
Growing soil or herb soil
The particularly fine structure of growing and herbal soil is intended to make it easier for cuttings and young plants to take root. It is low in nutrients or only lightly fertilized so as not to burn young roots. It is particularly suitable for plants that do not need many nutrients, such as herbs.
Its pH value is between 4.5 and 6.5, depending on the manufacturer.
Growing and herb soil consists of:
- Raised bog peat in various stages of decomposition
- In small quantities perlite
- In some cases, different weakly dosed fertilizers
Orchid potting mix
Orchid soil is probably the coarsest and, therefore, the airiest potting mix. Its structure is due to the rough pine bark, which is contained in almost all orchid soils. Thus, it hardly holds water and is ideal for epiphytes with delicate roots.
Fertilizer is usually added to the soil, leading to full bloom.
The pH value of orchid soil is between 5.0 and 6.8.
Included in orchid soil are:
- Pine bark
- Raised bog peat in various stages of decomposition
- Lime powder
- Various fertilizers
You can find more information about orchid soil and how to mix it in our orchid potting mix article.
Ingredients for self-mixed substrates
Instead of buying a ready-made substrate, you can also mix your substrate. You can choose the ingredients that bring suitable properties for your plant from various materials.
Below you will find the most common materials for substrate mixtures with their properties.
Activated charcoal
No products found. differs from other carbons in its extensive surface area. That is due to many delicate pores. 1g of activated carbon has a surface of about 1000 m2. Pressed activated carbon is used in water filters, for example.
In powder form, however, you can also add it to the substrate. It absorbs excess water, lowers the pH level, and has an antibacterial effect. Among other things, it neutralizes unpleasant odours.
In addition to water, the activated carbon absorbs nutrients. Unfertilized, it is an actual nutrient magnet. To ensure the supply of nutrients, you should therefore pre-fertilize it. Simply mix liquid fertilizer with water and activated carbon. When the water evaporates, you get a powder form again.
You can add the finished product to the substrate. Pre-fertilized, the activated carbon releases the nutrients to the plant over a more extended period instead of absorbing them.
In summary, activated carbon has the following properties:
- Improves drainage by absorbing excess water
- Has an antibacterial effect
- Prevents mould
- Lowers the pH value
- Absorbs nutrients (pre-fertilized, it slowly releases nutrients, making them accessible for the plant)
Pumice
No products found. is a volcanic aggregate, and it acts like lava granules. Since it is porous, it improves air circulation in the substrate, and it also improves drainage.
Particle sizes from 5 mm to 16 mm are best for your substrate.
The properties of pumice at a glance:
- Improves drainage
- Improves air circulation
- Temporarily stores moisture
- Can indirectly promote root growth and nutrient supply
- pH value: 7.0
Coconut chips
Coconut chips* or also called Coconut Husk Chips, are crushed coconut shells. They are an excellent alternative to pine bark because they are slightly softer, allowing the roots to grow better on them.
Because of their somewhat fibrous structure, they absorb water until they are wet. They rarely get drenched, and when they do, it takes a lot of effort.
Coconut chips may have a high salt content, depending on the supplier. So make sure to soak them before using them. Their pH value ranges between 5.2 and 6.8.
The properties of coconut chips at a glance:
- Fibrous structure
- Temporary water reservoir
- Release nutrients slowly
- Can absorb calcium and magnesium, release potassium and nitrogen
- Can have elevated salt levels
- pH value: between 5.2 and 6.8
Coconut Coir
Unlike coconut chips, coconut coir* (also called coconut soil and Coco Coir) consists of the palm trees’ fibres and the coconuts’ outer shell. The fibres are often pressed into cubes. That makes them easy to store and easy to portion.
Before use, the fibres are soaked in water. They absorb some of the water and thus gain volume.
Since coco coir contains almost no nutrients, it is often used in cultivation. Roots have no problem finding their way through the fibres, which also serve as a temporary water reservoir.
Like coco chips, coco coir can also have a high salt content. Its pH value is between 5.5 and 6.8.
The properties of coconut soil at a glance:
- Very fibrous structure
- Temporary water reservoir
- Low in nutrients
- Can absorb calcium and magnesium, releases potassium and nitrogen
- Can have increased salt values
- pH value : between 5.5 and 6.8
Lava granules
Lava granules*, like pumice, are a volcanic aggregate. The porous structure, which is formed when the hot magma cools, improves air circulation in the substrate. Due to its form, it also improves drainage.
Particle sizes from 5 mm to 16 mm are suitable for the substrate.
The properties of lava granules at a glance:
- Improves drainage
- Improves air circulation
- Temporarily stores moisture
- Can indirectly promote root growth and nutrient supply
- Comparatively heavy (can weigh down large pots and provide stability)
Mycorrhizal fungi
No products found. are fungi that usually form a symbiotic relationship with the roots of a plant. This association benefits both the plant and the fungus.
Studies show that mycorrhizal fungi can contribute to better growth, more prolonged flowering, and better resistance to pests and diseases.
However, some plants do not form this symbiotic relationship.
The properties of mycorrhizal fungi at a glance:
- Improved resistance to salts and heavy metals
- Improved resistance to pests, diseases, and drought
- Improved growth and more prolonged flowering
- Improved nutrient uptake
Perlite
Perlite (also called perlite) is a glass structure of volcanic origin. This glass structure has a vast surface area. Therefore, it is added to many soil mixtures.
No products found. serves as a water reservoir and aeration for the substrate. It is almost free of salts and has a neutral pH level of 7.0.
Cuttings are also frequently rooted in perlite.
The properties of perlite at a glance:
- Serves as a water reservoir
- Serves as aeration
- Contains little salt
- pH value: 7.0
Pine bark
No products found. is available in different particle sizes. The sizes 15-25 mm and 25-40 mm are most suitable for substrates. Pine bark retains moisture without getting wet.
Due to the very coarse structure, enough air reaches the roots. That is why orchid soil contains mainly pine bark. Pine bark removes some nitrogen from the substrate, with a pH value between 4.0 and 5.0.
The properties of pine bark at a glance:
- Absorbs moisture and releases it slowly
- It is structurally stable
- The coarse structure offers optimal air circulation
- Removes nitrogen
- pH value: 4.0-5.0
PON
PON, also called Lechuza-PON*, is a pure mineral substrate of the Lechuza brand. It is designed for the brand’s self-watering pots. Due to the small particle size, the water moves upwards towards the plant.
However, this small particle size is the undoing of some plants and can lead to root rot if misused.
PON consists of lava granules, zeolites, pumice, and slow-release fertilizer.
The properties of PON at a glance:
- Structurally stable, does not deform even under pressure
- Airier than pure soil, nevertheless only limited air circulation
- Becomes moist, not wet
- Due to fertilizer not being suitable for rooting cuttings and plants with sensitive roots
- pH value: 6.8
Sand
Sand* is very suitable for loosening up a substrate or increasing drainage. Some succulents and cacti are kept exclusively in sand.
You should use washed quartz or garden sand to avoid impurities, especially salts.
The sand itself contains virtually no nutrients. The pH value is between 6.5 and 7.0.
The properties of sand at a glance:
- Structurally stable and non-clumping
- Hardly any nutrients
- Holds almost no water
- Alone too fine for many plants
- pH value: between 6.5 and 7.0
Black peat
Black peat is the lower layer of raised bogs. With black peat, you can recognize almost no plant parts. It is poor in nutrients and is, therefore, often used to lower the pH value in the soil.
Due to its structure, it holds water particularly well and for a long time. The pH value is between 4.0 and 4.5.
The properties of black peat at a glance:
- Low in nutrients
- Fine structure, hardly any plant residues
- Stores a lot of water but is hydrophobic when dry
- pH value: 4.0-4.5
Sphagnum moss
No products found. is known to many plant lovers. It is often used for rooting cuttings and for air layering.
It has a loose structure, allowing air to reach the roots. Nevertheless, it can absorb large amounts of water and hold it for a long time. At the same time, it is not very susceptible to mould.
Often the peat moss is sold dried in bricks. If it is moistened, it gains volume.
The pH value is between 4.5 and 5.0. Sphagnum moss is low in nutrients.
When buying, make sure your moss comes from a sustainable source. Due to high demand, moss is becoming more common to be illegally taken from bogs.
The properties of Sphagnum moss at a glance:
- Absorbs and holds water very well
- The loose structure allows air circulation
- Low in nutrients
- pH value: 4.5-5.0
Clay Granules (LECA)
Clay granules*, also called expanded clay or LECA (Lightweight Expanded Clay Aggregate), are incredibly well-known and popular in hydroponics. The coarse structure of the clay balls allows the roots to grow ideally.
The coarse surface is ideal for temporarily absorbing nutrients. The problem with expanded clay is the pH value. Generally, this is around 7.0.
If misused, this can rise to 9 and above. At these values, the roots are no longer able to absorb nutrients.
Therefore, expanded clay is quite suitable as an additive in a substrate mixture but not as the sole substrate in the long term.
Before using LECA, you should boil it and wash it several times.
The properties of clay granulate (LECA) at a glance:
- Structurally stable
- Retains moisture, not wetness
- Improves drainage
- Allows air circulation
- pH value: 7.0; levels up to 9.0 possible if used incorrectly
Vermiculite
The rare layered silicate No products found. is lightweight yet takes up quite a bit of space. Due to its layered structure, oxygen quickly reaches the roots. It has a limited water-retaining effect.
With a pH of 7.0, it is pH neutral.
The properties of vermiculite at a glance:
- A large surface area with little weight
- Good aeration of the roots
- Temporary water storage
- Without nutrients
- pH value: 7.0
White peat
White peat is the counterpart to black peat. This is the upper peat layer of a raised bog. This is where you will find more non-rotted plant remains.
White peat also contains hardly any nutrients and is mainly used for its water-retaining properties.
Its pH value of 3.0 to 3.5 makes it even more suitable for regulating the pH value in the substrate downwards.
The properties of white peat at a glance:
- Stores a lot of water
- A fine structure and richer in plant residues
- pH value: between 3.0 and 3.5
Worm humus
No products found., also called worm castings, is considered a natural fertilizer, the excrement of compost worms. The quality of worm humus depends on the feed of the worms.
The humus contains nitrogen, potassium oxide, calcium oxide, various enzymes, and microorganisms. It also retains water well. The pH value is about 6.5.
The properties of worm humus at a glance:
- Fine structure
- Stores water well
- Rich in nitrogen, potassium oxide, and calcium oxide
- Contains various enzymes and microorganisms
- pH value: 6.5
Zeolite
If you own a pool, you have probably come into contact with zeolite*. There the porous mineral is often used as a filter in pools and lakes.
In substrates, it is often used to improve drainage and temporary storage of water. The mineral also positively affects air circulation and can even prevent nutrients from being flushed out.
In the long term, zeolite raises pH by binding acid.
The properties of zeolite at a glance:
- Porous structure
- Improves air circulation
- Soaks up and stores water and nutrients
- Improves drainage
- Raises pH value through acid binding
What you should know about peat
Many finished soils contain peat. That is mainly due to its properties, which are very suitable for plants.
Since peat is quite delicate, it has a large volume with a moderate weight. In addition, peat stores water well. At the same time, it can drain the substrate by allowing excess water to seep away.
However, peat has its price. Peat cutting often eradicates peatlands. Considering that about 1 mm of peat is produced each year naturally, it is foreseeable that we will not see renaturation to the point before mining.
Therefore, I would like to encourage you to purchase sustainable, that is, peat-free soil. In the meantime, there are good alternatives to peat. These include compost, bark humus, and wood fibre.
The same is true for Sphagnum moss. Even though much of the moss is now grown sustainably, there are still producers who harvest it directly from bogs. This also damages the ecosystem.
Dry peat has a hydrophobic effect, which means it repels water. If you water your plant and the substrate contains peat, the water may run off the surface and not seep through the substrate. Your plants will die of thirst even though you water them regularly.
The role of the pH value in the substrate
You may have read above about the pH values of different substrates and their components, wondering why pH is essential in the first place.
The pH value indicates how strongly a solution or substance is acidic (0) or alkaline (14). The scale ranges from 0 for acidic to 14 for alkaline.
Battery acid, for example, has a pH of less than 1, while caustic soda has a pH of up to 14. Water, with a pH of 7, is considered neutral.
In plants, the pH value determines how well roots can absorb nutrients. In addition, not all microorganisms survive at all pH levels.
For most houseplants, the pH of the substrate should be between 6.0 and 7.0.
An organic potting mix for most houseplants
Now that you know all the options for a substrate mix, I want to show you a simple blend. This one is suitable for most houseplants and is based on the Aroid mix.
I used it for a longer time before I switched to a more complex mix for my arum plants.
For the simple mix, you need coco coir*, No products found., No products found., fertilized activated charcoal, No products found. and some No products found.. If you like, you can also add No products found..
Do you have everything? Then let’s get started!
- Mix 2 parts coco soil with two parts pine bark
The base of this substrate consists of pine bark and coco soil. This way, you ensure a coarse structure with good air circulation. In addition, the ingredients do not get wet but retain moisture temporarily. - Add 1.5 parts of perlite and 1 part of fertilized activated charcoal
The perlite helps the substrate drain while retaining a bit of moisture. The moisture is released over time to the other components and the plant. At the same time, it supports air circulation.
Before using perlite, you should moisten it to counteract dust formation.
Activated charcoal avoids unpleasant odours and slowly releases the nutrients contained in the fertilizer to the plant. It also improves drainage. - Refine the substrate with 1 part worm humus and 0.5 parts sphagnum moss
With the worm humus, you add a water reservoir and natural fertilizer. In addition, you enhance the mix with the enzymes and microorganisms it contains. Sphagnum moss also serves as a moisture retainer without degrading air circulation. - Mix thoroughly once
Now that all the ingredients are present in suitable quantities, everything needs to be mixed evenly.
Mineral substrates and the “passive Hydroponics”
So far, we have only dealt with organic substrates. However, you also have the possibility to keep most of your plants in hydroponics.
For this, we usually use passive hydroponics. The houseplant is kept in a pure mineral substrate and supplies itself with water through a reservoir.
It is crucial that you do not use organic substrate. It gets waterlogged and promotes root rot, mould, and bacterial growth.
Mineral substrates usually consist of lava granules, pumice, and zeolites. With this growing type, you must supply the plant with nutrients via fertilizer. In addition, the pH level of the water and its ingredients, such as lime, must be regulated.
For these reasons, keeping plants in passive hydroponics is often unsuitable for beginners.
Substrate recipes for different plant families
Substrate for arum plants (monsteras, philodendrons, syngoniums, …)
Substrate for cacti and succulents
Don’t miss out!
Sources
(2019). The utilization of activated carbon as micronutrients carrier in slow release fertilizer formulation. ui.adsabs.harvard.edu. https://ui.adsabs.harvard.edu/abs/2019E%26ES..359a2009P/abstract
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