Potassium, together with nitrogen and phosphorus, is one of the three most important plant nutrients, without whose sufficient and balanced supply the highly nutritious tomatoes neither grow healthily nor develop tasty fruit. It is true that special potassium fertilization is not usually necessary, since the mineral is administered in sufficient quantities when a full supply is available. In some cases – such as on light, sandy soils or soils that tend to have a low pH, as well as during prolonged drought – a potassium fertilizer may be useful. Avoid overdosing by using natural materials such as wood ash.
Why potassium is so important for tomatoes
Potassium, or potash for short, chemically abbreviated K, is indispensable for many metabolic processes and also ensures that plants remain healthy and vigorous. It is not only tomato plants that need the mineral for a regulated water balance, which is why a potassium deficiency is often noticeable in the form of withering leaves. If plants are supplied with too little potassium, they can no longer absorb water despite sufficient liquid supply and literally die of thirst. However, highly nutritious fruit vegetables such as tomatoes need the nutrient for another reason: the tasty red fruits only develop if they are adequately supplied, and they only develop their typical aroma if they are. At an average of 3.8 grams per square meter, tomato plants have an above-average requirement. If this requirement is not met, the fruits will remain small, pale and not very aromatic.
Special potassium fertilizer necessary?
If you supply your tomato plants with a complete fertilizer or an NPK fertilizer (compound fertilizer), additional administration of the mineral is basically not necessary. This also applies if you supply your plants with organic fertilizers, as compost, manure and the like also usually contain the nutrient in sufficient quantities. Fertilizing naturally even offers tangible advantages compared to supplying artificial fertilizers: Not only do you keep the organic nutrient cycle alive, you also avoid oversupply with natural fertilizers. This can have serious consequences, as can an undersupply, which becomes apparent in symptoms such as growth inhibition, lack of fruit yield and various diseases. In any case, it makes sense to have a soil analysis carried out before a planned fertilization period and in the event of suspected deficiency symptoms. This will show whether there is actually a potassium deficiency.
Potassium is one of the ten most abundant minerals on earth, but is usually only present in bound form and is therefore difficult for plants to access. These are dependent on dissolved forms, as these are more easily absorbed through the roots. Nevertheless, a special potassium fertilizer is only necessary in certain cases, namely when
- a potassium deficiency has been determined by a soil analysis
- the crop is grown on light, sandy soils
- the garden soil tends to have a low pH value
The latter is particularly important for tomato plants, as they thrive best in soil with a pH between 6 and 7. Slightly acidic soils with lower values can be easily enhanced with an organic potassium fertilizer so that the demanding fruiting vegetables can thrive there.
Recognizing and treating potassium deficiency
Potassium deficiency is quite common in tomato plants due to their comparatively higher requirements when fertilizer is inadequate. You can recognize it by these typical symptoms:
- Leaf edges turn brown
- older leaves fade, become yellowish (chlorosis)
- formation of characteristic white spots
- turn brown in the further course and fall off
Furthermore, plants affected by a deficiency are highly susceptible to pest infestation and various diseases, especially the dreaded late blight.
Make your own potassium fertilizer from ash
To treat the symptoms and their cause, you do not need expensive special fertilizers from specialized stores. Instead, the deficiency can be treated naturally with simple wood ash. The material also has an invaluable advantage: it contains almost all the essential nutrients, so it can be used in general for fertilizing tomatoes. How to make an effective fertilizer from ash yourself, will show you the following instructions.
which wood ash is suitable
Wood ash accumulates on many occasions in the house and garden, for example when firing the fireplace in winter or at the summer barbecue. However, not all ash can be used for fertilizing due to the high content of heavy metals and other pollutants. Unsuitable for an organic potassium fertilizer are especially:
- Residues from commercial barbecue charcoal or barbecue briquettes.
- Ash from surface-treated or impregnated wood
- Ash from newspapers, cardboard or recycled material
- Residues from clothing, plastic or other burnt waste
It is also better to avoid the typical kindling aids such as newspaper, toilet paper rolls, etc., as these are also heavily contaminated with lead, chromium and other toxins. Of course, you don’t want to find heavy metals like these in your homegrown tomatoes, which is why you should make a point of using natural wood when making wood ash. Sawdust, small dry branches or dry leaves are all suitable for lighting the fireplace or barbecue.
potassium fertilizer from wood ash
To make the potassium fertilizer, the wood ash must first be thoroughly cooled. The starting material is perfect when it has burned to a gray powder. You can also collect it for a longer period of time and store it in a well-sealed container. For a liquid fertilizer, stir the wood ash into a water-filled watering can made of alkali-resistant material. You should dose the amount so that a maximum of 30 grams of ash is applied per square meter of area. Dose the fertilizer very sparingly, because wood ash is very rich in nutrients, dissolves quickly and therefore overfertilization happens quickly.
apply wood ash directly into the bed.
As you can see, you don’t need complicated instructions for making a potassium fertilizer, because you can basically do without dissolving it in water. Instead, apply the wood ash directly into the tomato bed, with half a cup to a small cup per plant (depending on growth height and need) being perfectly adequate. Sprinkle the material on the soil and then lightly work it in, followed by ample watering of the plant. Fertilizing with three to four portions per growing season is sufficient, so that a maximum amount of 100 grams is not exceeded.
Avoid overfertilization with potassium
You can also avoid potassium overfertilization by mixing the wood ash with sand or soil. In addition, compost can be enriched with the material. These instructions show you how:
- Layer compost in the classic way
- Always chop the material well and spread it in thin layers
- Spread wood ash thinly between the individual layers
However, very small amounts of wood ash are sufficient to make compost with potash. About 30 grams per square meter of compost is perfectly adequate.
Home remedies for potassium supply
In addition to wood ash, various other materials available in the household are of course also suitable, which you can use for making a fertilizer enriched with potash. For such a potassium fertilizer you do not need extensive instructions, but only
- potash dissolved in water (potassium carbonate, on the baking shelf)
- self-prepared plant yeast (especially comfrey and nettles)
- well chopped banana peels
- dried coffee grounds
- horse manure, alternatively cattle manure