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Most plants need a resting phase in autumn and winter in order to be able to grow well again in spring and summer. But that doesn't mean they shouldn't be fed during this rest period. However, they then need a fertilizer whose effect is not primarily aimed at growth. Thomaskali has proven to be ideal. So it's high time to take a closer look at him.

Thomaskali fertilizer

In general it can be said that Thomaskali fertilizer is used for the so-called basic fertilization of the soil and plants. It is a so-called PK fertilizer. PK stands for phosphorus and potassium. Both nutrients are absolutely necessary in order to be able to actually exploit the full growth potential that a soil contains. They are typically applied outside the vegetation phase of the plants. However, they still make an important contribution to plant growth in spring and summer. Thomaskali also contains other important nutrients. It is therefore a sophisticated mixture of several components that are coordinated with one another.

notice: Because of its original form, this type of fertilizer is still often called Thomas flour. However, since the flour caused an extremely high level of dust when it was spread, it is now available almost exclusively as dust-free granules.


As already mentioned, Thomaskali is basically a mixture. In addition to the two central elements phosphorus and potassium, there are other elements in it. The mixture and the mixing ratio can differ depending on the manufacturer. The following composition applies as a standard mixture:

  • Phosphorus - 8%
  • Potassium or potassium oxide - 15%
  • Magnesium or magnesium oxide - 6%
  • Sulfur - 4%
  • Fillers and other materials depending on the manufacturer - 67% (rest to 100 percent)

Incidentally, nitrogen as a typical nutrient that can be found in many fertilizers has no place in Thomaskali. The reason for this is quickly explained: nitrogen specifically and directly promotes the growth of the plants, which should of course be avoided during the resting phase.


Thomas potash fertilizer works best on slightly acidic soil. The specific mode of action depends on the properties of the individual elements that make it up:


Phosphorus is an extremely important part of the tissue cells of a plant. It is also one of their most important nutrients. If a plant can absorb enough phosphorus from the soil, it promotes and stabilizes its growth. It also plays a major role in controlling a plant's metabolic processes. In the soil, phosphorus ensures that larger crumbs are formed from individual small soil particles. And that in turn prevents siltation or soil erosion.


Potassium strengthens the cell tissue of plants and makes an important contribution to effective gas exchange with the roots. It also ensures stable cell walls and increased internal cell pressure. Without potassium, no plant could survive because without the stability it promotes, it could not withstand the varying weather conditions. Incidentally, the formation of new leaves would also not succeed without it.


Magnesium regulates the pH value in the soil and also ensures that other nutrients are available in it. Plants also need it to process proteins and carbohydrates. Incidentally, magnesium also makes an important contribution to making photosynthesis possible.


Plants also need a small amount of sulfur to thrive. But it is becoming increasingly rare to find it in the soil. This is exactly why this element is found in practically every Thomaskali mixture. It also makes a significant contribution to revitalizing the soil or soil.


Thomaskali is only fertilized in late autumn or in winter. As already mentioned, it should only be applied when the plants are dormant. The ground should neither be deeply frozen nor covered with snow. It is applied either directly by hand or with a small shovel. When it comes to dosage, it is essential to follow the manufacturer's instructions, which can usually be found on the packaging. They usually indicate a ratio of quantity per square meter.


It goes without saying that the prices of Thomaskali depend on the composition and the manufacturer. In addition, of course, the purchase quantity also plays a role. Basically, it can be said that a larger container also leads to a lower price per kilogram. If you buy one kilogram of Thomaskali, you currently have to reckon with an average price of 8 euros. If you buy a ten-kilo sack, however, the price per kilo is already reduced to €1.50 to €2.

Admittedly, this fertilizer is relatively expensive. However, the costs are quickly offset because you can limit yourself to inexpensive nitrogen fertilizers when fertilizing during the growth phase.

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