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There are many different points of view regarding feeding cacti with fertilizers. This is a rather controversial issue and, as a rule, it is based on someone's experience. Since cacti are very peculiar plants, fertilizers are special for them. Let's figure out what kind of food elements are needed for cacti, and to what extent.
The first nutrient that is mentioned when it comes to feeding common plants is necessary for growth. In cacti, the need for nitrogen is extremely limited due to some physiological characteristics and, above all, their slow growth. If there is a lot of nitrogen in the soil, or a lot of nitrogen turned out to be in the applied fertilizer, then the stem of the cactus begins to grow rapidly, becomes loose and watery. Many children and offspring appear, but they do not develop into full-fledged plants, the skin of a cactus does not have time to grow and bursts. Wounds and scars appear that rot or crust over, as a result, the plant will be disfigured or die. Therefore, organic fertilizers are not used for cacti, except in very small doses for epiphytic, rapidly growing cacti. However, it is impossible to completely abandon nitrogen, i.e.if you plant a cactus in clean sand and do not feed, nitrogen starvation may occur.
Potassium is a vital nutrient for cacti, it regulates their growth, promotes the formation of dense leathery covers that protect the body of cacti from temperature extremes, winds and bright sun. Potassium also affects the timely ripening of shoots, stimulates good flowering and ripening of berries. It is very difficult to determine the lack of potassium on cacti, it usually manifests itself in the absence of flowering, pallor of the skin, sometimes in the appearance of a bronze tint. Potassium deficiency can be observed in calcareous soils. This is explained by the fact that during liming, an excessive concentration of calcium ions in the soil solution is formed, which makes it difficult for the plant to enter the potassium and magnesium cations. Therefore, for a harmonious balance, one part of potassium should have two parts of lime.
It should be remembered that the same symptoms as with a lack of potassium can also be explained by disturbances in care - a lack of light or high air temperature. Therefore, do not rush to feed - an excess of potassium is harmful to cacti - growth slows down, the roots die off.
If nitrogen is needed for vershoks, then phosphorus is an element that stimulates root growth. It also influences the setting of flower buds and flowering, fruit ripening and seed vitality. Therefore, mineral fertilizers with the NPK formula are most suitable for cacti, where equal parts of nitrogen and potassium and more phosphorus. Lack of phosphorus can be suspected if cacti grow very slowly, even if the temperature and light conditions are observed, they do not bloom.
For cacti, calcium is a very important element due to the fact that it is a building material for spines, bristles and hairs. So, for example, back in 1938, when studying the species Cephalocereus senilis, it was found that more than 85% of the dry weight of plants consists of calcium oxalates (Cheavin WHS. The crystals and cystolites found in plant cells. Part 1: crystals. Microscope. 1938; 2: 155-158.). The lack of calcium on cacti will first appear on acidic soils - this is slow development and growth, a weak root system, thin soft spines, fragility and fragility of the plant.
A healthy strong cactus is practically not injured when it falls from the windowsill, the maximum that threatens it is that the children will break off, the peduncle will break. But a healthy cactus, which has enough all the nutrients, can be shaken off, put in a pot and put in place. Its needles will not break, the trunk will not crack, the roots will not come off. Largely due to proper mineral nutrition.
The composition of the correct fertilizer for cacti
We found that cacti need very little nitrogen than all other plants, so organic fertilizers are almost never used by cactus growers (except in exceptional special cases). Many years of experience in growing cacti shows that fertilizers in liquid form are most effective. They are more convenient for the cactus grower to use, because it is easier to dose if you have purchased too concentrated fertilizer. By itself, a high concentration of minerals in an aqueous solution does not affect anything, the ratio between them is important, and we can change the concentration by diluting it with water. General recommendations are that the salt concentration of the complete fertilizer should not exceed 1 gram per 1 liter of water.
Such ratios of minerals as, for example, NPK 5-10-5 or 20-30-20 (diluted 4 times of the recommended dose) are considered successful to stimulate flowering. At the end of flowering NPK with a formula of elements in equal parts, for example, 5-5-5 or 20-20-20 (1/4 dose) or 10-10-10 (1/2 dose).
Some experts consider these fertilizer doses too high. For example, the fertilizer from Schultz, which is very popular in Europe, has the formula NPK 2-7-7, i.e. nitrogen is even less than traditional. Another cactus fertilizer "GrowUp" has the formula NPK 2,5-5-4. This fertilizer is specially designed for cacti and does not need to be diluted three or four times. In all other cases, the rule works: "it is better to underfeed than overfeed".
It should be especially noted that the requirements of various genera of cacti for minerals differ: epiphytic and semi-epiphytic cacti (first of all, Rhipsalis Rhipsalis, Schlumberger Schlumbergera, Epiphyllum Epiphyllum or Hylocereus Hylocereus), do not require a high calcium content in the soil, do not tolerate calcareous soils. But they like a sufficient content of vermicompost in the soil and you can feed them with ordinary fertilizer for decorative flowering indoor plants, using a dose, depending on the concentration, equal or slightly less than recommended by the manufacturer.
When to feed cacti
Top dressing of very low concentration can be applied every two weeks, from March to September. During the dormant period, and this is the period from October to March, cacti are not fed. Remember that flowering does not always coincide with the growing season! And if flowering occurs in autumn - winter, this is not a reason to feed, usually it is enough to just slightly increase watering.
It is also worth reducing or stopping feeding in the spring-summer season, when rainy, cloudy weather lasts for a long time. Metabolism slows down during this period, plants slow down in growth, do not require a large amount of nutrients.
In addition, top dressing begins no earlier than three weeks after transplantation.
By the way, sometimes you can read in the literature about feeding cacti by some non-traditional methods, for example, sugar or castor oil, etc. However, we strongly do not recommend using such funds on cacti, since everything can end quite badly. If, nevertheless, you decide to try a new remedy, then try it on one (experienced) not very valuable cactus, observe it for a long time. It may take a year, but the results will please you. But you should not try out various means unknown to you on the entire collection of cacti.