Garden and kitchen waste can be used as fertilizer for your plants and is also good for your soil. Here you can find out everything about fertilizing with compost.
The term "compost" comes from the Latin compositus, which means "composite". Compost can be made from a wide variety of organic waste. And as colorful as the starting materials are, their properties can also be as varied.
You can use what is produced by the conversion of beneficial microorganisms to fertilize your plants and improve the soil.
Compost: properties and composition
Compost is humus formed from organic waste. As already mentioned, the properties of compost depend on the raw materials used:
Biocompost: Compost made from organic waste and some herbaceous green waste is called organic compost. This has a very high nutrient content, as a lot of nutrient-rich material was used. This makes it usable like a plant fertilizer.
Green compost: A compost that is only made from green waste and material that is difficult to decompose is called green compost. It is less nutrient-rich and therefore promotes the formation of humus rather than fertilizing the plants.
Organic and green waste compost are of course only two cornerstones of a wide range of possibilities. Mixtures between these are also possible, the properties of which then lie somewhere in the middle between the extremes. Last but not least, the duration and conditions during composting also influence the end product:
Fresh compost: A four to eight week old compost that has not yet rotted completely. The structures of the starting materials are still clearly recognizable.
Finished compost: A compost that has rotted for at least six months. There is almost only crumbly, pleasantly smelling material here.
Maturity compost: You get a maturity compostafter two to three years of rotting. At this stage, even the sturdiest woody material has been converted to humus.
Tip: Compost has a C/N ratio of about 15:1 to 25:1 - depending on the starting materials and the rotting time. The C/N ratio indicates how much carbon (C) and how much nitrogen (N) a material contains. From a C/N ratio below 20:1, the material is increasingly broken down by microorganisms and nutrients are released rather than humus being formed. From a C/N ratio of 25:1, degradation is inhibited and humus is more likely to form because microbial mineralization is inhibited. So compost represents a borderline case and depending on the type of compost, the fertilizing or soil-improving effect can predominate. Fresh composts and those composed of nutrient-rich material tend to have a low C/N ratio, while mature composts and those composed of nutrient-poor material have a larger C/N ratio.
Summary of properties and composition of compost:
- Organic compost is made from nutrient-rich waste and has a similar effect to a plant fertilizer
- Green compost is made from nutrient-poor waste and has a soil-improving effect
- Fresh compost is produced after about six weeks and is neither completely decomposed nor composted
- Finished compost is produced after about six months, then most of the material has decomposed and has been reassembled into humus
- Maturity compost occurs after two to three years, then all material is decomposed and converted into humus
- Depending on the C/N ratio of the material used and the rotting time, the compost can release nutrients through mineralization or improve the soil as humus
Compost as fertilizer for plants?
Basically, any type of compost is suitable for plant fertilization and soil improvement. However, the extent to which an effect occurs depends heavily on the type of compost used. In the best case, nitrogen, potassium and phosphorus are in a balanced ratio to each other. However, it is more often the case that the phosphorus and potassium content is significantly higher than the nitrogen content. Unfortunately, this nutrient ratio is suboptimal for the nutrition of plants, their nitrogen requirements are usually much higher. We therefore recommend that you use compost together with another fertilizer. Our Plantura organic fertilizers are ideally suited, as is the organic universal fertilizer, which is tailored precisely to the needs of theplants are balanced and have the right nutrient ratio.
The richness of trace nutrients in compost, which your plants need just as urgently as the main nutrient elements, deserves special mention. In the table below you will find the suitability of different types of compost as fertilizer. Plant fertilizers primarily provide nutrients, soil fertilizers primarily improve the soil.
| compost type | Priority Feature | Description |
|---|---|---|
| Fresh Compost | Plant Fertilizer | Contains few of the stable humic acids typical of fully composted material. Acts more like a layer of mulch when applied and breaks down quickly as a source of nutrient humus. |
| Finished compost | Plant Fertilizers and Soil Fertilizers | Is a valuable supplier of both nutrients and permanent humus, which promotes soil life and fertility in the long term. |
| Mature compost | Soil fertilizer | Supplies a lot of permanent humus, but fewer nutrients. Contains many of the very stable humic acids that make a valuable contribution to improving soil properties. |
| Biocompost | More like plant fertilizer - depending on the implementation stage | Is generally more nutritious than green compost, resulting in faster conversion and higher nutrient content at all conversion stages. It is better suited as a plant fertilizer. |
| Green waste compost | Rather a soil fertilizer - depending on the degree of implementation | Is generally less nutrient-poor, produces more permanent humus when spread, because conversion is inhibited by the higher C/N ratio. |
Tip: Nutrient humus is humus that is unstable and easily degradable due to its high nutrient content. It can provide plant nutrients but does not permanently improve the soil.
Summary of compost as fertilizer:
- Compost can basically be used as a plant and soil fertilizer
- Fresh compost and organic compost are more effective as plant fertilizers
- Mature compost and green waste compost act more as soil fertilizer
- Ready compost has plant fertilizing and soil fertilizing properties to about the same extent
Effect of compost on plants and soil
The effect as a plant fertilizer is similar to the effect of organic fertilizers. thePlant nutrients are released depending on the weather, so they are not available all of a sudden, but only gradually. This circumstance prevents plant damage from acute or permanent over-fertilization and is also beneficial for the preservation of humus in the soil. In addition, the slow and microbial conversion creates a natural long-term effect.
The soil fertilizing effect is usually in the foreground when using compost: the swellable and light humus flakes improve the water storage of light soils. As a result, water is better retained in the soil. On the other hand, when applied to heavy soils, compost causes loosening, which promotes aeration of the roots and drainage of water. This avoids waterlogging, which hinders the growth of most plants.
Tip: You will be surprised, and rightly so, that compost is said to have such opposite effects on different types of soil. However, the apparent paradox can be explained with the pore size: A sandy soil has many large pores in which the water cannot be held. To understand this, simply imagine a layer of coarse gravel: the water just flows through it and the layer soon dries up again. Clay soils behave in exactly the opposite way in terms of pore sizes. They have very many tiny soil pores. Water is held in these so well that when it rains a lot, the entire floor can be saturated with water because it cannot drain downwards. Plants then suffer from the lack of oxygen at the roots. In addition, they cannot even reach the water in the tiny gaps: it is held far too firmly in the soil pores. Humus now acts as a mediator. It does not have very large or very small, but medium-sized pores. These can hold water better than sand and drain it better than clay. And the roots can absorb it optimally from these medium-sized gaps.
Humus molecules alone can hold many nutrients on their surface so that they are available again later. In connection with clay minerals, the so-called clay-humus complexes are also formed, which have outstanding properties in terms of nutrient and water storage. Only through them is it possible to form larger "crumbs" that are visible to the naked eye. Due to the large number of loosely connected molecules involved, the surface area of clay-humus complexes is very large. This explains their ability to store many nutrients and water. The crumbs are also elastic and thus reduce compaction- So your floor will forgive you when you walk over it and cushion your load.
The humic acids that form the stable permanent humus are dark brown to black in color. Your soil benefits greatly from this property in spring: since dark soil absorbs more sunlight, it can warm up more quickly. Incidentally, warming is also promoted by good soil aeration, since air in the soil can be heated faster than water. And good soil aeration can also be achieved with humus.
Last but not least, the little heroes of your soil should definitely be mentioned here: microorganisms. Because these are involved in almost all processes in the soil. Since organic matter is their livelihood, spreading compost is a feast for them. It provides them with the energy and materials they need to provide nutrients, mine and convert raw materials, and perform many other activities that benefit your plants.
Tip: Unfortunately, compost can also have negative effects on your soil or your plants: If there is heavy rainfall in autumn while the soil is still warm and the soil life is accordingly active, nitrogen leaching can result. It is also possible to carry fungal pathogens and also unwanted seeds of wild herbs if the temperature in the compost heap was not high enough during rotting. See the Create compost section below for more detailed information on hot and cold rotting.
Summary effect of compost on plants and soil:
- The nutrients contained in the compost are released slowly and over a long period of time depending on the weather, which protects the soil and plants
- Humus molecules - especially in combination with clay minerals - can form stable crumbs that loosen the soil, bind nutrients and water and also make heavy soil more permeable to water, which improves the growth conditions for plants
- Dark coloring and better soil aeration promote faster soil warming, allowing plants to start growing earlier in spring
- Compost offers an optimal breeding ground for the important microorganisms in the soil
- Compost may contain pathogens or weed seeds, and under unfavorable conditions nitrogen can be leached out of it
Use compost as fertilizer
The necessary quantities and the use of compost can be found in the table below. When using it, however, you should definitely note that compost should not be buried deep. Since it contains many air-breathing microorganisms, which should live on for further processing of the compost, the availability of air while at the same time being protected from the immediate weather is essential. Optimally, compost is incorporated fully but shallowly. A special case is mulching, where a thick layer is applied and not worked in.
| Usage | Quantity | Compost |
|---|---|---|
| Mulching (covering planting areas) can be done every 3 - 5 years | 50 - 70 l/m², which corresponds to a layer about 5 - 7 cm thick | Green waste/fresh compost |
| Soil improvement | 20 - 30 l/m², which corresponds to a layer of about 2 - 3 cm | Green waste/ready compost or green waste/ripening compost |
| Annual maintenance of lawns and beds | 2 - 4 (max. 15) l/m², which corresponds to a layer approx. 0.2 - 0.4 cm thick | Green waste/ready compost or organic/ready compost |
| Fertilization of shrubs, lawns or beds | 5 - 10 l/m², which corresponds to a layer of about 0.5 - 1 cm thick | Organic/fresh compost or organic/ready compost |
| Production of potting soil | Up to 50% by volume | Depending on the nutrient requirements of the cultivated plant: High: organic/ready compost Medium: green waste/ready compost Low: green waste/ripening compost |
Put out compost when?
Compost is best applied in winter or early spring. You should avoid potentially rainy and warm seasons such as late summer or early autumn. Nutrient-rich composts in particular release many nutrients at warm soil temperatures, which can be washed out in heavy rainfall. This is not only a pity for the plant nutrients, the environment is also polluted when nitrogen enters natural bodies of water via the groundwater. Composts that are poorer in nutrients - mature composts and green waste composts - release fewer nutrients and are therefore safer to use. The application should then take place in overcast, not too dry weather.
Summary: When to apply compost?
- Bring compost in winter or earlyspring, never in late summer or early autumn from
- If possible apply compost in damp, overcast weather
Compost in the bed: How much compost per square meter?
Depending on what you ultimately want to achieve, you can apply a layer of compost from 0.2 to 7 cm thick. Annual care to maintain the humus content and to provide a basic stock of nutrients only requires a thin layer. Targeted soil improvement with finished or mature compost to increase the humus content in the soil already requires somewhat larger quantities. In both cases, however, the compost is incorporated flat. The mulching with fresh compost from green waste takes place in a very thick layer, which, however, is not incorporated. You can mulch every three to five years. More detailed information on the use of compost in other areas is provided in the following section.
Where do you get compost?
If you want to create your own compost to take advantage of its extensive benefits, you can find out more about the structure of a compost bin in our special article. A brief guide to proper composting can be found in this article. Creating your own compost has many benefits, but it also requires a little planning and care. So you may have to use a bit of brains to stratify waste or regularly move it to aerate it so that the composting can proceed properly. Various, more or less necessary additives can also play a role here. With the help of our special article, you can also mix compost yourself.
Possibly composting is too much work for you or you need high-quality compost quickly to fill a planting hole or create a new bed? You can also easily buy compost - or rather humus - in various forms. The cheapest option here is certainly a local recycling center that offers either organic compost and green compost separately or a mixture of both. But there are also affordable options for less rural areas. Potting soil, which is available in sacks of various sizes, contains, among other things, compost forms of different rotting degrees. Here, too, the starting materials can vary, so that the soils offered can differ greatly. In this advanced article you will learn everything you need forneed to know how to buy hummus.