Poting soil, also known as planting substrate or simply substrate, is, in contrast to naturally grown garden soil, a mixture of different ingredients put together by humans. These soils are tailored to the needs of indoor and other potted plants. The following article reveals which soils there are and how you use them.
What is potting soil?
Potted and balcony plants need a suitable substrate in the pot, because without it they will not grow. It is important to choose a high-quality product, because the plants are completely at the mercy of the material and its ingredients - in contrast to the plants in the garden or even in the wild, which let their roots grow where there are nutrients and water there.
Houseplants, which are usually only repotted every few years, are particularly dependent on good potting soil. This must be firm enough so that the plants can find support in it, but at the same time they can both store water and nutrients and release them again when needed. In addition, potting soil is ideally composed in such a way that it neither hardens nor becomes muddy. As a rule, normal garden soil is not suitable for this purpose as it often has the wrong composition and is not fine-crumbed enough.
Potting soil or potting soil?
Although the terms potting soil and potting soil are often used interchangeably, there are still some subtle differences:
| potting soil | Planting soil |
|---|---|
| for pots, tubs and flower boxes | for planting perennials or trees in the garden |
| sole substrate | Soil improvers and compost substitutes |
| mostly mixed with slow-release fertilizer | Coarser structure, contains less fertilizer |
In principle, you can of course also use potting soil for your potted plants, but you should then add additional components such as a slow-release fertilizer and, if necessary, some quartz sand for a finer structure. Conversely, potting soil is also suitable for use in the garden bed, although you probably won't choose it. High-quality potting soil (or potting soil) is often more expensive than potting soil.
What pH value does potting soil have?
With the exception of special soils that are adapted to the needs of ericaceous plants and therefore have an acidic pH value in the range between 4 and 5, normal potting soil is brought to a neutral pH value between 6 and 7. Since many of these soils are made from acidic peat, manufacturers add lime and/or quartz sand. Most plants grown in pots and other containers grow best at a neutral pH.
The ideal pH value of potting soil varies depending on the needs of the plant
Excursus
Plant substrates without soil
Potted plants do not necessarily need potting soil for he althy and beautiful growth. Instead, you can also place the plants in a so-called planting granulate, which usually consists of clay balls. This procedure is used primarily - but not only - in hydroponics and has many advantages compared to soil culture. Plant granules are cleaner, free of mold, putrefactive bacteria, pests, weed seeds, etc., making expanded clay etc. ideal for allergy sufferers. The material also stores large amounts of water without clumping together or causing the plant to suffer from waterlogging. Instead, the moisture is released exactly when it is needed.
What types of planting and potting soil are there?
The garden center has a huge selection of different potting soils, so you stand in front of them and can't really decide. Which soil is ultimately suitable for your own project? The following overview will help you make a decision.
| potting soil | Ingredients | Intended use |
|---|---|---|
| Planting soil | Peat or compost, lime, fertilizers, additives | Garden |
| United Earth | White or raised bog peat, loam or clay, fertilizer | Garden and pot culture |
| Compost soil | peat-free compost-based soil with additives | Garden and pot culture |
| Universal Earth | depending on the variety based on peat or humus with fertilizers and additives | for all potted plants, vegetable plants, herbs, fruit trees |
| potted plant soil | depending on the variety based on peat or humus with fertilizers and additives | can be used universally for all house and balcony plants |
| Orchid soil | coarse substrate made of bark, coconut fibers and peat | Special soil for orchids |
| Cactus and succulent soil | high proportion of quartz sand | for drought-loving cacti and succulents |
| Rose Soil | often contains a lot of clay as well as a nutrient combination tailored to roses | for roses in the garden and in containers |
| Hydrangea soil | loose, humus-rich substrate with acidic pH value | various varieties for blue and other colored hydrangeas |
| Geranium soil | Special mixture with high long-term nutrient content | for geraniums and other heavy-consuming potted plants |
| Herbal clay | loose, nutrient-poor substrate with a high quartz sand content | for many herbs and other plants with low nutrient requirements |
| growing soil | loose, nutrient-poor substrate with a high quartz sand content | for sowing and cuttings |
| Rhododendron and ericaceous soil | nutrient-rich, low-lime special soil with acidic pH value | for rhododendrons, azaleas, hydrangeas, blueberries, lingonberries and cranberries |
Do you really need all these special earths?
In view of all these special soils for roses, hydrangeas, cacti, geraniums, etc., many hobby gardeners ask themselves whether they actually make sense or whether normal potting soil doesn't also serve its purpose. In fact, some special soils are essentially unnecessary, as the needs of the respective plants can also be met with conventional potted plant soil. You can save yourself expensive rose or geranium soil, for example, as both types thrive very well in normal, humus-based potted plant soil.
The situation is different with soils that are intended to meet the very specific needs of certain species. Rhododendron and ericaceous soil is suitable for all plants that prefer an acidic environment. Cacti and succulents, on the other hand, need a rather dry and nutrient-poor substrate, while orchids cannot tolerate potting soil at all. These feel most comfortable in a coarse substrate made of pieces of bark and other fibers.
Peat or compost?
Many potting soils are based on the natural raw material peat. Although this is biodegradable, it is still highly problematic for both plants and the environment for various reasons.
“Bogs and peat bogs bind four times more carbon dioxide than tropical forests.”
- Draining peat bogs: Peat bogs are valuable habitats worth protecting that provide a home for many rare plants and animals. In addition, these ecosystems, which have become rare due to urban sprawl and intensive agriculture, store climate-damaging carbon dioxide. If the moors are now drained for the purpose of peat mining, not only is an invaluable ecosystem destroyed, but at the same time huge amounts of fossil CO2 are released.
- Depletion of peat deposits: Due to the drastic decline in peat bogs and the ongoing peat mining, the deposits will be exhausted within a few years. For this reason alone, more sustainable alternatives should be sought and found.
- Disadvantages for potted plants: In particular, the cheap “no-name” potting soil from the discount store is largely made from peat orpeat waste. Do not use these soils because you are not doing your plants any favors. Peat-based potting soil tends to become rock hard when it is dry and can then hardly absorb any water. The roots cannot grow unhindered and are also hindered in absorbing water and nutrients.
In view of these disadvantages, it is important to use peat-free potting soil. But what options are there?
This video presents the disadvantages of peat and a possible alternative:
Rezept gegen Klimawandel: Wie diese Blumenerde helfen kann | Quarks
What is peat-free or peat-reduced soil?
There are several ways to replace peat moss in potting soil, either in whole or in part. For several years now, potting soil based on coconut fibers, for example, has been offered quite frequently in hardware stores and supermarkets. This usually comes as an ultra-light package to which water is added at home and which then swells and can be used.
The rapidly renewable raw material coconut is extremely user-friendly, but has itself been criticized for ecological reasons. The dried coconut fibers ultimately have to travel a very long way to Germany, which in turn causes carbon dioxide. Coconuts are also grown on plantations that had to make way for rainforests.
Compared to coconut fiber, xylitol, which is obtained as a by-product of charcoal production, does not cause any additional environmental impact. The material was only recently discovered for use in potting soil and shows extremely positive properties with regard to the growth and flowering behavior of potted plants. Xyliter soil is characterized by a very high air permeability and contains a similar amount of humic acid as peat soil. This keeps the pH value of the flower substrate at a consistently he althy level.
What is compost soil?
In addition to the peat substitutes mentioned, compost soil is also a very suitable planting substrate for many potted plants. This also has the advantage of being absolutely environmentally friendly, as it preserves the natural cycle of life and turns organic waste into a valuable source of nutrients. But be careful: Do not put your potted plants in pure compost, but mix one part of ripe, fine-crumbly compost and two parts of processed, clayey garden soil. Alternatively, buy suitable compost soil from the garden center.
Compost soil is environmentally friendly, nutrient-rich and, at best, free
How do you recognize high-quality planting and potting soil?
Whether a potting soil is good or not can hardly be determined without opening the bag. In addition, you will often only find out whether it is high-quality soil during use - i.e. when your plants are already in it. As long as your house and other potted plants are growing splendidly, blooming profusely and otherwise appear he althy, the potting soil is generally fine. Otherwise, please pay attention to these features when purchasing:
- Buy peat-free soil.
- Stay away from cheap potting soil from the discount store.
- This contains too much s alt and too many fillers and will harm your plants.
- Prefer mixtures of organic raw materials.
- This also includes organic fertilizers, such as: E.g. horn shavings or compost.
- When opening the package, the soil should not smell musty or even rotten.
- However, an intense earthy smell is normal and desirable.
- The individual components of the soil should be evenly mixed.
- Only a few large parts should be visible.
- The fresh potting soil should be fine-crumbed and slightly moist.
A high-quality potting soil must be able to store moisture well and release it again when necessary. In addition, it must not become hard if it dries out, but must absorb the water quickly when watered again.
Tip
Most commercial potting soils are mixed with a slow-release fertilizer. However, this does not mean that you no longer need to fertilize your plants! Quite the opposite, because the nutrients are used up after about four to six weeks. From this point on, regular fertilization makes sense.
Store potting soil correctly
Only buy as much potting soil as you currently need. The material is not suitable for long storage as the nutrients it contains decompose very quickly, especially in warm, humid weather. If there are any soil residues left over, store them in a sealed bag and keep them as cool and dry as possible. The dark basement is more suitable for this purpose than a sunny balcony. By the way, many garden centers and hardware stores store potting soil incorrectly: the bags are stacked on top of each other in the blazing sun and are waiting for their buyers. Therefore, if possible, choose goods that have been stored in cool rooms and away from the sun.
Change potting soil regularly
Potted plants should be repotted regularly
Potting soil is exposed to a lot of stress and is therefore used up very quickly. In addition, over time, the natural product accumulates with unsightly things such as mold spores and other fungi, bacteria and even pests that lay their eggs directly in the soil. Fungus gnats, for example, are often brought into the house with fresh potting soil. These reasons speak for completely replacing the soil in the pot every one to two years to keep pathogens and pests at bay. Furthermore, your plants benefit from fresh soil on a regular basis, as it is finer and looser than the old soil and therefore more ventilated.
Excursus
How to dispose of used potting soil?
Used potting soil is best disposed of with organic waste or buried in a garden bed. The material can be easily “hidden” in borders or spread thinly over the compost and mixed with it.
Mix your own potting soil – instructions and tips
Until the 1970s, it was common for plant lovers and nurseries to mix their own flower and potting soil. These mostly consisted of compost and peat, loam and clay, sand, charcoal and other substances in different compositions, depending on which plants should grow in them.
Good potting soil is a mix of different materials
Even today, you can still find numerous recipes for your own mixtures in gardening books and on the Internet. The basis for this is usually fine-crumbly, sandy-loamy garden soil, which our grandmothers used to take from molehills. This is loose and has just the right consistency for potting soil. Add green compost or other humus (such as bark compost) as well as primary rock powder and horn meal. It is also important to note the correct pH value and, if necessary, check it with a test strip from the pharmacy. If the pH value is too low, add some garden lime (without any other additives!). Now mix the ingredients thoroughly so that the potting soil is as uniform as possible and the individual components are evenly distributed.
Ideal mixing example for a self-mixed universal soil:
- one third of mature compost
- two thirds of fine garden soil
- both materials are finely sieved!
- for loamy garden soil: a handful of quartz sand
- for sandy garden soil: a handful of clay granules
- a handful of bark humus (available commercially)
- two to three grams per liter of horn meal
- if necessary, some garden lime
Most potted and house plants feel extremely comfortable in this potting soil. To prevent any unpleasant surprises from developing in the form of pests or weeds, you should disinfect the finished soil for a few minutes in the microwave (at 600 to 800 watts) or for half an hour in the oven (at 75 °C).
Frequently asked questions
Can I also put topsoil in the flower pot?
Topsoil is the top layer of the earth's topsoil, which is approximately 20 to 30 centimeters thick. This is essential for plant growth as it contains many nutrients and is home to active soil life. In principle, you can also use topsoil for your potted plants, but the material also contains admixtures of weed seeds, small stones, root residues and animals. Planting or potting soil, on the other hand, has been cleaned so that you don't have to worry about wild growth in the flower pot.
The potting soil is moldy. What should I do now?
First of all: Not every whitish layer on the surface of the potting soil is mold. In many cases it is just limescale deposits that have accumulated from watering with lime-containing tap water. They are harmless. Real mold, on the other hand, occurs when potting soil with high organic content is watered too heavily and therefore too moist. Remove the top, moldy layer of soil, replace it with fresh substrate and water less. Good pot drainage also helps, for example by mixing in sand to increase water drainage.
Mushrooms suddenly grow out of my flower pot. Is this bad and what can I do about it?
If mushrooms suddenly grow in the flower pot, you have probably watered too much. However, the fruiting bodies have nothing to do with the quality of the potting soil, because fungi feed on dead biological material and therefore appear wherever it can be found. Remove the fruiting bodies and water your plants less and the “problem” will disappear on its own.
The potting soil in the freshly opened bag stinks. Is she bad?
If fresh potting soil “stinks”, i.e. a strong smell comes out of the bag that has just been opened, this is no reason to be alarmed. In particular, soils with organic ingredients such as horn meal or horn shavings, guano, compost, bark humus, etc. often smell very intense. Be happy about it (and hold your nose while doing it) because the smell is a sign of the good quality of this soil: the microorganisms it contains are currently doing their work and converting the organic ingredients into nutrients that the plants can easily use. If the scent bothers you, let the soil in the opened bag air out in a less frequented place for one to two days before use.
Tip
If you only want to use the best potting soil for your plants, you should read the test reports from Stiftung Warentest. It was only in July 2019 that she took a closer look at various potting soils and made clear recommendations.
