Late autumn - mid to late October - is the right time to apply mineral fertilizers such as lime, magnesium, potassium or phosphate fertilizer if necessary. However, this is usually only necessary if a soil test shows potassium or magnesium contents or pH values that are too low. In this case, slow-acting fertilizers such as potash magnesia (patent potash) and carbonate of algae or dolomite lime are recommended for sustainable improvement.
When and how should you fertilize the vegetable garden in autumn?
Late autumn (mid to late October) is the ideal time to supply the vegetable garden with mineral fertilizers such as lime, magnesium, potassium or phosphate fertilizer if necessary. Slow-acting fertilizers such as potash magnesia (€16.00 at Amazon) (patent potash) or carbonated algae or dolomite lime are recommended for a sustainable improvement in soil quality.
Which mineral fertilizers are there and how they work
Mineral fertilizers are sometimes under general suspicion of being “artificial fertilizers” or even “bad chemicals”. This is not true, because most nutrients such as potassium or magnesium occur in nature primarily or only in mineral form, i.e. as components of rocks. Most of the raw materials for mineral fertilizers are obtained in mining. If they are only chopped up (for example ground), lime and potash fertilizers in particular only develop their effect very slowly, but are all the more lasting. For this reason, such mineral fertilizers should be applied in autumn so that they can fully develop their effect in the next season.
Phosphorus
The fertilizer form of phosphorus is phosphate (P2O5). This nutrient is very important for flower and fruit formation as well as root growth and energy metabolism. In the event of a deficiency, not only the development of fruits (and thus the harvest!) suffers: the plants often remain small, appear strangely rigid and the leaves turn dark to dirty green, sometimes even reddish. An excess of phosphorus, on the other hand, hinders the absorption of other nutrients such as nitrogen, iron and zinc and can severely pollute water bodies if they are washed out.
Potassium
Potassium (K) is fertilized as potash s alt. It plays a very important role in water balance and material transport, strengthens plant tissue and increases resistance to cold and pathogens. When there is a potassium deficiency, the tips and edges of the leaves lighten and then turn brown, starting on the older leaves. In addition, the leaves often curl up and the plants appear limp and wilted. An excess of potassium in the soil, on the other hand, hinders the absorption of magnesium and calcium.
Magnesium
Magnesium (Mg) is an important building block of leafy greens and promotes protein formation and other metabolic processes. If there is a deficiency, the older leaves initially turn yellow, later brownish; the leaf veins, however, remain green. An excess of magnesium in the soil is very rare. However, when it occurs, it can hinder calcium absorption.
calcium
Calcium (Ca), the main component of lime, is important for water balance and various metabolic processes in the plant. A direct calcium deficiency (in which young leaves turn yellow and shoot tips snap) is quite rare. However, many gardeners are familiar with blossom end rot on tomato and pepper fruits, where the fruit has an initially watery spot on the tip that later turns black-brown to gray. Something similar can occur with zucchini and pumpkins. The main trigger for this is a poor calcium supply - usually not because of a deficiency in the soil, but because an uneven water supply or excessive fertilization with other nutrients (especially nitrogen) hinders the transport of calcium to the fruits. In addition, calcium, especially in the form of lime, is important for the pH value of the soil and for the soil structure.
Tip
Plants only need trace nutrients such as boron, iron, copper, manganese, molybdenum and zinc in small quantities, but they need them just as much as the main nutrients.
