Potassium Fertilizer: Properties & Do-It-Yourself Tips

Potassium fertilizer serves special properties of the plants. We will show you when it is right to use special potassium fertilizer.

You can find tons of different fertilizers on the market. Potassium fertilizers are available, among other things, as single-nutrient fertilizers, but there are also potassium-rich universal fertilizers that have a higher potassium value than other compound fertilizers. We will tell you when you need to use potassium fertilizer and what you should consider when using potassium fertilizers.

Potassium fertilizer: properties and composition

Potassium is a very soft alkali metal and, along with nitrogen and phosphorus, one of the most important plant nutrients. In the soil, the leaching and the mobility of potassium are rather low. Only about 1 to 2% of all the potassium present in soil is found in soil solution - and only that 1 to 2% of potassium is directly available to plants.

Potassium is a natural component of every soil. In Germany, its share in the soil is 0.3% to 3%. When doing a soil analysis, the ideal potassium level should be between 13 and 25 mg for heavy soil and 8-10 mg of potassium per 100 g of garden soil for light soil. Potassium is present in the soil in the form of positively charged ions and is mostly attached to the clay minerals and to the humus bound. These bonds are relatively loose and the ions can be easily released again, making them available to the plants. If the potassium is built into the crystal lattice of the silicates, it can no longer be absorbed by the plants and is therefore bound.

Plants prefer potassium for uptake, however, other nutrients can inhibit plant uptake of potassium. These include calcium, magnesium, ammonium and also sodium. In addition, low pH can also inhibit the absorption of potassium. If the pH value falls below 4, the plant roots even release the potassium again. It is also easy to move around in the plant and is transported to where it is needed. Since potassium is important for cell structure, young leaves are always richer in potassium than older ones.

Effect of potash fertilizers on plants

Plants need potassium for various processes such as:

• control of metabolic processes
• regulation of the water balance
• Regulation of the function of the stomata
• Increasing the resistance of plants to infections
• Increased frost hardiness of the plants (a high potassium content in the vacuoles lowers the freezing point of the cell sap)

The potassium is stored by the plants in the vacuoles and is involved in the regulation of turgor. The turgor, also called turgor pressure, describes the pressure that the cell sap exerts on the cell walls. In certain compartments of plant cells, an osmotic potential is built up with the help of the accumulation of potassium. This should be higher than in the vicinity of the cells. This allows water to flow into the cells, turgor is built up and the plant cells are filled with water and become taut. However, if the substrate is too salty, for example, the exact opposite reaction can occur. Then water flows out of the cells and the plants become limp.

Can Too Much Potassium Harm Plants?

An oversupply of potassium can also cause damage to your plants and trigger various symptoms. These include growth inhibition, root burns, damage to the leaves or even necrosis on them. Unfortunately, these symptoms are similar to those of an undersupply. However, there is usually hardly any direct potassium excess. When such damage occurs, it is generally salt damage because plants can absorb relatively high levels of potassium without major problems.

detect potassium deficiency

Plants show very different symptoms when there is a lack of the nutrient potassium. These symptoms include, for example, the yellowing of the leaf edges, which is also known as chlorosis. The edges of the leaves can even turn brown and die, i.e. become necrotic.

These necroses always form first on the older leaves and are initially only recognizable as small black dots. If there is a severe potassium deficiency, the plant transfers its potassium from the older leaves to the younger ones. For this reason, the symptoms always appear first on the older leaves. Another symptom can also be that the leaves curl and curl. In addition, the plants wither and the leaves only hang limp on the plants. This is also called withering. Growth disorders and an increased susceptibility to diseases are also associated with a potassium deficiency. This can also affect plant viability and tolerance to frost and drought.

Summary: Recognizing Potassium Deficiency in Plants

• Leaf edges turn yellowish
• Necrosis on older leaves
• Leaves curl and buckle
• plants wither
• growth disorders
• Higher susceptibility to diseases
• Lower stability

Various Potash Fertilizers & Potassium Content

Basically, only water-soluble potassium salts are used as potassium fertilizers. It is also important to know that calcium and potassium act as antagonists in the soil. Therefore, these two nutrients must be applied in the right ratio.

A special potassium fertilization is of course necessary in the case of an acute deficiency. You can find out whether there is a deficiency by analyzing the soil or by the symptoms of a deficiency that occur. But especially in autumn you should rely on potassium-rich fertilization for the winter hardiness of lawns and shrubs. Below we present the different types of potassium fertilizer:

Patent potash/Kalimagnesia

Patentkali fertilizer is a special fertilizer containing potassium (K₂SO₄), magnesium (MgSO₄) and also contains sulfur. The fertilizer consists of 30% potassium oxide, 10% magnesium oxide, 15% sulfur and is actually called Kalimagnesia, but the trade name is Patentkali. These fertilizers are water-soluble and the nutrients are quickly available for our plants. It is also extracted from the naturally occurring mineral kieserite. Since Patentkali is chloride-free, it can also be used for sensitive plants and shrubs such as rhododendron (rhododendron) or boxwood (boxy) be used. Patentkali is available in fine to coarse grains and is suitable for basic and top fertilization - unfortunately it is not suitable for liquid fertilization.

potassium sulfate

Potassium sulfate is the potassium salt of sulfuric acid (K₂SO₄) and is used as a fertilizer for plants sensitive to chloride, such as raspberries (Rubus idaeus) or blackberries (Rubus caesarean section Rubus). Potassium sulfate contains 50% potassium and 45% sulfur and is a low-salt fertilizer. It is also used in homeopathy, as an extinguishing powder and in many areas of industry and technology. This fertilizer is a white salt that is fine to coarse-grained and is also suitable for liquid fertilization.

Potassium fall fertilizer

Potassium is present in most autumn fertilizers because a sufficient supply of potassium promotes the frost hardiness of plants. Since potassium is particularly important for winter or frost hardiness, you should not do without it in autumn fertilization. This effect can be compared to an antifreeze, because the potassium is stored in the plant cells and thus lowers the freezing point of the cell sap. The cell thus remains functional. The cell sap would expand when it freezes, like water, and destroy the cell, but this does not happen with the potassium.

Potassium Lawn Fertilizer

If you want to have a healthy and strong lawn, potassium fertilization is important. Potassium fertilization is particularly important in autumn, as a sufficient supply of potassium can prevent snow mold infestation. In our Plantura Organic Autumn Lawn Fertilizer therefore contains an extra portion of potassium so that your lawn survives the winter safely. With a lawn fertilizer, the potassium strengthens the resilience of the plants, it protects against drought, cold and diseases - it is important to Fertilizing the lawn in spring and also the Fertilizing the lawn in autumn not to forget.

Thomas potash/phosphorus potash fertilizer

A fertilizer that consists mostly of potassium and phosphorus is also called Thomaskali. Thomas potash has a granular structure and consists of 8% phosphorus (P₂O₅), 15% potassium oxide (K₂O) and 6% magnesium oxide (MgO). The fertilizer is also found under the term "Thomas flour", it is a by-product of steel or iron production.

Make your own potassium fertilizer

You can also make some high-potassium fertilizers yourself. Various manure and broths, for example, are suitable for this.

comfrey manure

A manure made from comfrey (symphytum) is made from 1 kg of fresh comfrey leaves, which are crushed and fermented with about two hands of marigolds in 10 liters of water. This manure can be used to strengthen plants and contains many nutrients. Comfrey manure contains a particularly large amount of nitrogen and potassium. The liquid manure is therefore ideal for fertilizing vegetables that consume a lot and as an additive to compost.

dandelion manure

For an optimal dandelion slurry, put about 2 kg of fresh dandelion leaves and flowers in 10 liters of water (Taraxacum) at. This slurry has a stimulating effect on plant growth and contains a lot of potassium and calcium. You can spray the manure undiluted over plants and over the ground.

fern broth

For the fern broth you need about 5 kg of fresh fern (Pteridium aquilinum). You can also take about 1 kg of dried fern and put it in 10 liters of water. The fern is pickled for a day and the broth is boiled for about half an hour. The fern broth mobilizes the potassium from the compost and from the soil and can also be used against lice.

However, you can not only use manure and broth for fertilizing, but also other products that arise in the household.

wood ash

You can find wood ash in your fireplace or on the charcoal grill. This is ideal for fertilizing, because the ash contains a lot of potassium, lime, phosphorus and iron. But the ash is not suitable for all plants. Those that need acidic soil should not be fertilized with it, as it neutralizes the soil. These plants include orchids (Orchidaceae), rhododendrons, peonies (Paeonia), daffodils (Narcissus) and many more. However, certain plants are particularly happy about a portion of ashes. These include tomatoes (Solanum lycopersicum), gooseberries (Ribes uva crispa), potatoes (Solanum tuberosum) and roses (pink).

NPK fertilizer In addition to potassium, they also contain nitrogen and phosphorus. In our special article you will learn everything about the advantages of NPK fertilizers.