Buy compost or make it yourself?

Compost is a valuable component of many potting soils. Here we explain where to buy it and how to mix compost yourself.

In the garden areas of DIY stores, in garden centers and nurseries, one increasingly sees not only the well-known peat-containing potting soil, but also those that consist largely of compost. These composts - often in organic quality - declare war on the overexploitation of endangered moorland. The production of potting soil could thus again take place in a recycling economy. This article contains a definition and a distinction from pure compost, a list of possible secondary components and also a brief comparison to peat. Finally, you will find a compilation of different products as well as instructions for mixing your own compost.

Compost and compost are by no means two terms that can be used synonymously: while compost is the pure product of composting, compost is a mixture that contains compost. Compost can be divided into different types and degrees of maturity. Green waste compost refers to compost made from rather nutrient-poor green waste, while biocompost is compost made from nutrient-rich organic waste. Composts that are poor in nutrients are decomposed significantly less in the soil and accordingly provide more humus to improve the soil, while nutrient-rich composts provide more plant nutrients. Fresh compost has only been composted for four to eight weeks, is rich in nutrients and is quickly broken down by microorganisms in the soil. Under good conditions, finished compost only occurs after five to six months and offers fewer nutrients, but in return is more resistant to microbial degradation. It takes one to two years to produce ripening compost - this is extremely stable, but provides hardly any nutrients.

To produce compost soil, ready-made and mature compost as well as green waste compost can be used particularly well.

Summary DifferencesCompost and compost:

• Compost refers to the pure rotting product, compost soil means mixtures that contain compost, among other things
• Compost soils contain secondary components that are intended to complement the compost properties
• Organic compost is far more nutritious than green compost
• Fresh compost is young and nutrient-rich, finished compost about half a year old and less nutrient-rich; Mature compost is 1 - 2 years old and low in nutrients
• The more nutrient-poor a compost is, the more stable humus it contains, which is retained
• The more nutritious a compost is, the less stable humus it contains and the faster it decomposes
• Ready compost and mature compost are the most commonly used composts in compost soil

Compost soil: definition and benefits

Compost soil - referred to as compost substrate in the professional world - is potting soil that contains a lot of compost. Since compost is often relatively rich in nutrients and therefore s alty and also often has quite high pH values, it is only very rarely used in its pure form: so-called additives or secondary components in compost soil are intended to balance the chemical and physical properties of the compost. Mineral components such as sand and broken bricks, clay minerals such as bentonite and vermiculite, perlite, lava rock, rock flour, expanded clay and pumice are used as aggregates. Organic secondary components such as wood fibers, xylitol, bark humus, coconut fibers or even rice husks can also be used. With the right combination of main and secondary components, compost should enable optimal growth conditions.

Tip: Our Plantura organic soils also use compost and contain structurally stable green compost with additives such as wood fibers and clay. They are also approved for organic farming and do not require peat. Our Plantura organic compost soil consists of 60% compost and is pre-fertilized so that the plants feel completely comfortable.

Excursion: Technical terms for substrates

• A material is called “inert” when it does not significantly affect the nutrient levels and pH of its environment. Chemical reactions with this material also hardly take place at all.
• A material is "structurally stable" if it is not degraded by microbial processes and its volume and porosity are stable over long periods of time.
• The air capacity describes how many air-carrying, large pores a material has.
• The water capacitydescribes how many water-bearing, medium and small pores a material has.
• Nitrogen fixation is possible when organic matter contains many carbon compounds but little nitrogen. Microorganisms then extract the nitrogen they need to survive from their environment in order to break down the material. As a result, plants growing in the area lack nitrogen. A deficiency can then be prevented by “compensating fertilization” with a long-term nitrogen fertilizer.

Aggregates in compost substrates

Additional components in compost are referred to as additives. The mixing ratio of the compost with a selection of different additives should ensure the best possible properties of the substrate in terms of aeration, structural stability, water capacity or weight.

Aggregate	Features	Effect in the substrate
Sand	quartz grains; slightly acidic, high air capacity, permeable, structurally stable, heavy	Improves aeration and water permeability, makes substrates heavier, requires regular watering
Broken bricks	Recycled/Faulty Bricks; porous, water-retaining, structurally stable, light	Improves ventilation, water permeability and water retention (to a small extent), all from around 30% by volume
Bentonite	sound; nutrient-binding, water-storing, easily wettable	Increases water holding capacity, stores nutrients and protects against over-fertilization, easy to moisten
Vermiculite	clay mineral; very good water storage, nutrient binding, easy to wet, pH value 8, expensive, contains a lot of magnesium	Increases water retention capacity, ensures even moisture, stores nutrients and protects against over-fertilization, easy to moisten
Perlite	Weathered, Crushed, Heated Obsidian; inert, pH 7.5, very porous, light	Improves ventilation and structural stability (substrate sags less), makes substrates lighter, ensures even moisture (everything from approx. 30 vol%)
Foam Lava	volcanic rock; porous, high air capacity, frost resistant, light	Increases structural stability (substrate sags less) from approx. 30% by volume, improves ventilation
Pumice	volcanic rock; porous, high air/water capacity, veryeasy	Increases structural stability (substrate sags less) from approx. 30% by volume, improves ventilation and ensures even humidity
Rock flours	Crushing Rock; acidic to alkaline, contain plant nutrients, form clay minerals	Supplies main and micronutrients for plants over long periods of time, increases the clay content of soil in the long term and improves crumb structure and water holding capacity
Blähton	Highly heated expanded clays; porous on the inside, structurally stable, high air capacity, light	Increases structural stability (substrate sags less) from approx. 30% by volume, improves water permeability and aeration, makes substrates lighter, requires regular watering
Wood Fibres	Recycled, usually made from softwood; high air capacity, not structurally stable, nitrogen-fixing, low water capacity, pH 5-6, low in nutrients	Improves aeration and water drainage, breaks down microbially, fixing nitrogen, raises pH and sags (needs balancing nitrogen fertilization), requires regular watering
Xylitol/Lignite	Lignite precursor, crushed; low in nutrients, structurally stable, high water and air capacity, slightly acidic (peat-like properties)	Improves aeration and water holding capacity, can be modified with lime and fertilizer as required, protects against over-fertilization
Bark Humus	Crushed fermented bark; medium water and air capacity, contains a lot of potassium, phosphate and trace nutrients	Improves aeration and water drainage, improves water holding capacity to a lesser extent, protects against pH fluctuations
Coconut Flour (Cocopeat)	Coconut shell abrasion; high air capacity, good water capacity, easy to wet, light, sometimes s alty (observe declaration, especially potassium, chloride, sodium), otherwise low in nutrients, structurally stable	Improves aeration and water drainage, reduces water holding capacity, increases structural stability (substrate sags less), makes substrates lighter; Possibly strong fertilizing effect, which must be taken into account when fertilizing
Rice Husks	"straw husk" of rice grains; very light, very high air capacity, low water capacity, structurally stable, nitrogen fixation possible, low in nutrients, pH value adapts to other substrate components	Improves aeration and drainage, requires regular watering, may trap nitrogen(compensating nitrogen fertilization necessary), usually increases structural stability (substrate sags less)

Compost substrates and peat substrates in comparison

Peat extraction is harmful to the climate, it destroys habitats and disrupts the water balance of entire regions, since moors can absorb and store huge amounts of water. But peat substrates are still the rule, especially in professional horticultural production, and alternatives are only the exception. This is not least due to the undisputed qualities of peat.

Properties of peat

Its properties, which we list below, make it the ideal starting material for the production of potting soil.

• Loose and permeable to air (white peat even when water is saturated)
• Very light and easy to transport when dry
• Can store many times its own weight in water
• Very low in nutrients, can therefore be fertilized according to the needs of each plant
• Structurally stable so does not sag and maintains aeration (white peat is more stable than black peat)
• Low pH, so acidic; it is easier to adjust to the desired pH with lime than to change a high pH substrate to a lower pH

Properties of compost

Compost as a substrate is much more difficult to use than peat:

• Depending on the starting materials, many of its properties are so variable that the production process has to be closely monitored in order to obtain a defined result
• Young compost is not structurally stable, can be very rich in nutrients and is then not suitable for growing young plants or for cultivating herbs and other lean plants that react very negatively to substrates that are too "fatty"
• The water holding capacity is high, but not as high as that of peat, which can mean that such a substrate has to be watered more frequently
• Compost is chemically less stable, it reacts to a fluctuating pH value and nutrient additions by changing its properties
• On the one hand, the pH value of compost is variable - depending on the raw materials it contains, and on the other hand, compost cannot be easily influenced to a desired pH value, since lowering it is more difficult than raising it

Of course, these difficulties can be circumvented to a large extent: By always carrying out the same targeted production of ripening compost from the same starting materials, which are as nutrient-poor as possible, you get a structurally stable, nutrient-poor compost with the desired pH value. The use of finished compost - which is a little more nutritious and less stable - is possible and reduces the amount of fertilizer to be added. The water storage capacity and structural stability can be significantly improved with xylitol - also known as lignite. In general, additives can bring a compost substrate very close to the properties of peat substrates - the difference then still lies in the production effort, in the purchase price and in an adapted use in professional horticulture.

Advantages of compost as a substrate base

Before you get the impression that the use of compost in potting soil only has disadvantages, let us now give you the decisive arguments that are gradually forcing producers and substrate manufacturers in Germany to rethink.

• Can be recycled over and over again from industrial by-products and waste
• Does not destroy the habitats of rare plants and animals - like peat cutting does
• Does not fuel climate change, since no bound greenhouse gases are released - as is the case with peat extraction
• Possibility of fertilizer savings when using nutrient-rich compost, which not only saves costs, but also reduces the degradation of limited fossil mineral fertilizers
• Can theoretically be produced in horticultural businesses - as was common a few decades ago - and also in private gardens according to one's own needs and then used to mix potting soil
• Production is not tied to a fixed location: there are no long transport routes, which are common with peat

Use compost

Compost soil - i.e. potting soil with compost - can usually be used like any other plant substrate. There are nutrient-poor and nutrient-rich soils available for various applications, as well as those with different pH values and different long-term fertilizing effects. Depending on the additives, they differ in their stability andwater holding capacity. So if you decide to use compost, it's best to take a look at your plants as you use them until you know exactly what's best for them.

Use compost

Green compost and mature or finished compost can be mixed and used as potting soil. In addition, all types of compost are used in the garden: as mulch material to be fertilized, to permanently increase the humus content or as plant fertilization and to stimulate soil life. This article tells you how you can use compost as soil or plant fertilizer.

Conclusion: buy compost or make it yourself?

There are pros and cons to both buying compost and mixing it yourself.

Buy compost: advantages

• Bought compost has a defined quality, the nutrients it contains, the pH value and the suitability of the soil are easy to read on the packaging
• The entire effort of producing or procuring compost as well as the procurement of additives is eliminated

Buy compost soil: Disadvantages

• High price and at the same time small sales
• Ready-mixed compost soils are often intended for a specific application, which can make the use of the substrate inflexible and make it necessary to purchase additional mixes
• Small packs mean a lot of packaging waste and the additives used have sometimes been transported long distances, both of which are not really environmentally friendly

Make compost yourself: Advantages

• Mixing your own substrates makes you independent of substrate manufacturers and their prices, as making your own is a fraction of the price of ready-made soils
• Because you can control which additives are used, you know exactly what is included and can make your earth extremely environmentally friendly and of high quality

Make compost yourself: Disadvantages

• Composting is quite a hassle, but you can avoid it by sourcing compost cheaply from a local composting facility
• All in all, you never know exactly what properties your own mixtures have, as you have to delve quite deeply into the topic of correct composting in order to be able to roughly assess your compost quality

In conclusion, it can be said thatminimalist hobby gardeners are better advised to buy ready-made compost (like our Plantura organic compost). This is especially true when not so large quantities are needed or when the time for garden maintenance is tighter than the budget anyway. Only gardeners with the really green fingers and the willingness to put in some effort can reap the benefits of self-mixed soil. If you belong to the group of die-hards, you can find out more about making your own compost here.