In the NPK nutrient triumvirate, potassium gives way to its fellow players during the growing season. Nitrogen (N) and phosphorus (P) drive growth and flower formation in spring and summer, supported by potassium (K) in photosynthesis and other physiological processes. The hour of potassium does not strike until autumn, because now it is important to prepare the plants in the garden and the lawn for winter. Read all information about the correct use of potash fertilizer here. You can find out here which fertilizers contain the optimal amount of the nutrient and at what prices they can be bought.

Importance of potassium as a fertilizer

Pure potassium is available to plants in the form of potassium chloride and potassium sulfate. Although it is one of the ten most common elements in the earth’s crust, there can still be a deficiency of potassium in the garden soil, as it can be easily washed out due to its mobility. The lower the clay content, the higher the degree of potassium loss due to leaching. In order to provide the ornamental and useful plants with a balanced supply of nutrients, potash fertilizers regularly compensate for the depletion of potassium. If no or insufficient potassium fertilization is carried out for several years, the following symptoms result:

  • Perennials lose their frost resistance and freeze back more strongly
  • Plants show stunted growth and growth depressions
  • Drought stress is more difficult to cope with, so that the leaves dry out from the edges
  • The needle tips turn brown on conifers
  • Lawns turn yellow and dry out over the course of winter

Fruit trees are particularly sensitive to potassium deficiency in that the leaves curl up, dry up and fall off. Since the fruits are no longer adequately supplied by the leaves, the harvest is less or completely. Roses signal a lack of potassium by turning the petals brown around the edges. The nutrient deficit in tomatoes, kohlrabi and radishes has a fatal effect, as lacerations and cracks form here.

Tip: Just as unfavorable as a lack of potassium is an excess of the nutrient in the soil. If there is an overdose of potash fertilizer, this results in leaf chlorosis with yellowed leaf surfaces and green leaf veins. The crumb structure in the soil is impaired, along with root burns.

Effects of Potassium

Potassium is a vital element for all flora and fauna and participates in numerous physiological processes. The following overview provides an overview of what exactly the effect on your garden plants and lawns consists of:

  • Strengthening of the cell tissue by increasing the cell pressure
  • Support of cell elongation and growth of the leaf surfaces
  • Favoring the uptake of CO2 to promote photosynthesis
  • Improvement of the metabolism for optimal water balance and robust drought resistance

By helping to increase cell sap pressure, winter hardiness is optimized. It is not so much the frosty temperatures that make your ornamental and useful plants or lawn grasses to create. Rather, the problem is the repeated alternation between thaw and frost. If potassium does not intervene in a supportive manner, the cell walls cannot withstand the pressure and burst. In the transition from winter to the beginning of the growing season, potassium actively participates in the growth of leaves, flowers, shoots and fruits.

Recommended potash fertilizers with prices

The administration of potassium chloride is not recommended in the home garden. Many of your ornamental and useful plants are extremely sensitive to this concentrated load of salts. 40 or 60 potash (KCI) is only used as a component of complete fertilizers, in addition to nitrogen, phosphate and trace elements. In contrast, potassium sulphate (K2SO4) is low in chloride and therefore ideally suited to supply the plants in the garden and your green areas with the essential nutrients. We looked over the shoulder of fertilizer experts and put together the following selection of recommended potash fertilizers for the home garden with prices for you:

The highly concentrated two-nutrient fertilizer contains 50 percent potassium sulfate and is almost free of potassium chloride. Supplemented with sulfur, this fertilizer is ideal for all types of cabbage, rapeseed, onions, sunflowers, soft fruits and vegetables as well as most ornamental plants and conifers.

  • Price for 5 kg: 13.90 euros (2.78 euros per kg) plus shipping costs

Patentkali / Potash Magnesia
The special potassium fertilizer is enriched with magnesium and sulfur for fruit and vegetables in the best quality. In autumn, Kalimagnesia helps you to achieve a hard-wearing, robust lawn carpet that even a harsh winter can not be afraid of. Thanks to the fine grain size, this potash fertilizer is qualified for basic and top dressing as well as for optimizing substrates. Only for liquid fertilization is Patentkali not suitable.

  • Price for 5 kg: 8.95 euros (1.79 euros per kg)

Purital potassium liquid fertilizer Potash
fertilizer in liquid form is perfectly suited for foliar fertilization . You can also comfortably supply your potted plants with the liquid potassium fertilizer without first having to dissolve the granules. With an NPK formulation of 0 + 0 + 20, the low-chloride preparation is a good choice for almost all ornamental and useful plants.

  • Price for 1 liter: 9.95 euros

Where the plants are not only lacking in potassium, Thomaskali comes into play. With an NPK formulation of 0 + 8 + 15, this potash fertilizer also has magnesium and sulfur in its luggage.

  • Price for 5 kg: 11.95 euros (2.39 euros per kg)

If you buy potash fertilizers in larger quantities, the prices per kilogram and liter drop significantly. The price of Patentkali is reduced to 0.92 euros per kg for a purchase of 25 kg.

Tip: Comfrey liquid manure makes a valuable contribution so that your plants do not suffer from a potassium deficiency in the first place. By repeatedly showering the garden soil with the plant manure every year in late summer and autumn, the vital nutrients are supplied to the roots in a natural way.

Soil nutrient analysis specifies the potassium requirement

Symptoms of nutrient deficiency can rarely be clearly assigned to the untrained eye. For example, stunted growth can be caused by a lack of potassium as well as by soil fatigue. You avoid the risk of improper fertilization and overdosing by entrusting a certified test laboratory with a soil analysis every 3 to 5 years. The experts give precise instructions on how to take soil samples in the garden and lawn. As part of a standard examination, main nutrients such as nitrogen (nitrate), phosphorus, potassium, calcium and magnesium are examined carefully. The result of the analysis then gives you specific recommendations as to whether and in what dosage fertilizer is required.


Autumn is the best time to use potassium fertilizer to prepare existing plants for winter. Since the ideal planting time for shrubs and woody plants extends from September to November, young plants with potash fertilizer get the best starting conditions. This is how easy it is to apply the fertilizer:

  • An appointment is ideal when the weather is slightly damp and the sky is overcast
  • Scatter the granulate on the soil to be planted and rake in
  • Apply the fertilizer grains to existing plantings and work them into the surface

Since the potassium content in the fertilizer is readily soluble in water, you then water the fertilized area with the watering can.

Lawn fertilizer

Before applying potassium fertilizer, please mow a lawn to a stalk height of 4-5 cm. Then distribute the fertilizer granules with the spreader in the dosage recommended by the manufacturer and irrigate the green area. The absorption of the nutrient is optimized by combing out all tangles and weeds beforehand with the scarifier. If you missed the autumn deadline, apply the potash fertilizer in early spring as soon as the soil temperature rises above 10 degrees.

If the winter flexes its muscles with freezing frost, your garden plants and lawn should be armed with potash fertilizer. In the form of potassium sulfate, the chemical element is available as a fertilizer for plants and grasses. Administered in autumn, potassium strengthens the cell walls and increases the cell sap pressure, which significantly increases winter hardiness. With low-chloride products such as Kalisop and Patentkali, you can buy inexpensive potassium fertilizers for the home garden that are also approved for ecological cultivation. The best time to use it is autumn. The soil should not be completely dry when you spread the fertilizer or apply it dissolved in water.

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