Wild Rose wrote:
We are always looking for the best way to care for our streptocarpus plants. What do you think is the most important thing to remember when feeding the plants. What fertilizer would you recommend?
Here is my translation of Pavel’s thought on fertilizersFertilizer.
Before we begin to talk about the fertilizer, let’s go back to the Streptocarpus species to understand where they get their nutrients from in nature. Since Streptocarpus are lithophytes (plants which grow in or on rocks) and grow at higher elevations on slopes and in rock crevices, the nutritional needs are very different from other plants that grow in low-lying areas. Because the soil in such places is constantly washed away by rain, the soil is poor.
Here I must say a few words about nitrogen
. Nitrate nitrogen is washed out much easier than ammonia, which is better fixed in the soil and less washed out by the rain. Also, composted organic matter tends to be smaller-sized than non-composted and, therefore, washed away more easily. Streptocarpus must survive in relatively "fresh" or semi-decomposed organic matter, which, in the process of decay, releases more ammonia nitrogen than nitrate nitrogen. Periodic drying of soil is an additional factor which contributes to the shift towards ammonium nitrate form. Thus, lithophytic plants have adapted to absorb small amounts of ammonia but not nitrates. That is why an excess of nitrate in fertilizer could concentrate in the substrate and inhibit plant growth. Water loss from leaves must be compensated by the uptake of water from the soil. During this process the dissolved salts accumulate in areas of maximum evaporation. Dry edges on the leaves of the plants quite often are not the result of starvation but of salt poisoning. The death of tissue or the weakening of protective functions due to this salt poisoning can allow bacteria and fungi to flourish.
Therefore, when buying fertilizer, pay attention to the form of nitrogen it contains. It is because Streptocarpus prefers the ammonium form of nitrogen that we sometimes see different recommendations on the use of fertilizers by different professional growers of Streptocarpus. Some recommend an equal ratio of nitrogen / phosphorus / potassium. Others advise less nitrogen and more phosphorus. And others, seeing that their plants have dry tips, take it for potassium deficiency and prescribe a high amount of potassium.
But let us consider the case of a fertilizer with a predominance of phosporus. In this case nitrogen fertilizers tend to be more in the ammonium form. On the other hand fertilizer high in nitrogen usually has nitrogen present in the amide or nitrate form and very little in the ammonium form. In this case your plants will not have enough accessible nitrogen, but total salt concentration may be poisonous. Excess of nitrogen (in any forms) promotes growth of microorganisms, which in turn aggravates the situation by further decomposition of organic matter into simpler and more soluble compounds. Fertilizer should not have a lot of nitrogen and more than 50% of nitrogen needs to be represented by NH4 + ion. Phosphorus.
Streptocarpus does not need a large amount of phosphorus. From the analysis of dead tissue we learned that Streptocarpus deposits the excess of phosphorus and calcium in the older leaves. Although an excess of phosphorus ages the leaves, it is not harmful for plants. Phosphorus inhibits fungal microflora and therefore slows down the aging of the substrate (soil). It is believed that phosphorus stimulates and accelerates flowering, but this is primarily at the expense of foliage. This is true for many flowering plants, but not for Streptocarpus since the main stimulator of flowering is light, especially in the red spectrum. Access of the phosphorus transforms calcium, iron, manganese, copper and other metals to insoluble form, which will have a negative effect on the quality of your plants.Potassium.
This element is very mobile and easily absorb by the plants, even in the small quantities. It is very important for plants, but an excess of it displaces other metals including ammonium nitrogen. Again, the golden rule is moderation. To prevent weakening of the plants the amount of potassium in your fertilizer should not be less than the total amount of nitrogen. With a lack of potassium plants obtain it from the older leaves which in turn exacerbates marginal necrosis. Simple potassium fertilizer can be in the form of potassium sulfate or potassium carbonate. The latter one can be easily obtained by taking it from wood ash. Since the ash too high in calcium we need to remove it. It easily could be done by adding 10part of water to 1 part of ash. Potassium and sodium dissolve easily. Calcium carbonate is practically insoluble, it remains in the sediment. This home-made fertilizer should not be used often because the ash’ solution is alkaline. It is advisable to apply it with fertilizer containing nitrogen in ammonium form. Excess potassium (without nitrogen in ammonium form) dramatically increases the osmotic pressure in plant cells, thereby increasing the risk of overwatering. Also the excess of potassium displaces magnesium and iron, which leads to chlorosis (deficiency of chlorophyll) especially between the veins.
As for complex fertilizers, the best ratio of nitrogen / phosphorus / potassium will be 20/10/30, but the first number should show not total nitrogen but its ammonium nitrogen (NH4 +)
Yes, of course, nitrates are also necessary but you do not need to have it in your fertilizer for two reasons: nitrates usually present in sufficient amount for Streptocarpus and bacteria in the soil convert ammonium into nitrate.
To make sure that your plants have enough nitrogen you could always add ammonium sulfate (1g/10L of water). Ammonium nitrogen is not only food for the plants but also growth stimulator. Flower stems become stronger and leaves are wider and thicker and the plants look healthier. Again, an excess of ammonium nitrogen makes leaf tissue loose and makes the plant susceptible to diseases. Ammonium sulfate is acidic. If you use ammonium sulfate without the buffer additive, you should neutralize it with ash solution monthly.
But since, as a rule, complex fertilizers contain nitrogen both in nitrate and in ammonium form, try to select one with higher amount of ammonium (NH4 +) than nitrate. To increase the amount of (NH4 +) you can add ammonium sulfate; it contains 20% nitrogen in the ammonium form. Since ammonium sulfate is acidic, it could be found among fertilizers used for acid-loving plants.
In order to make sure that your plants are not lacking nitrogen, one can add ammonium sulfate at the rate of 1 gram per 10 liters of water. Magnesium (Mg).
This very important element is part of chlorophyll, like iron is part of hemoglobin in humans. This element is usually absent in fertilizers. The manufacturers usually presume that your water has enough of magnesium and calcium in your hard water, in which the magnesium and calcium in excess. If you water Streptocarpus with distilled water, rainwater or water cleaned with reverse osmosis you need to add small amount of that element. You may add magnesium sulfate (about 5% of total fertilizer). If your substrate has vermiculite or dolomite you do not need to add magnesium. Calcium (Ca)
is also macroelement for the plants. Peat moss which is the main component in many commercially fertilizers soil has enough of it. Ca is part of the lime and manufacturers add a lot of lime to neutralize acidity of peat moss.
Excess of calcium is influence the color of your flowers. Especially it relevants to red color. Red pigment becomes purple or beat-like color. That is why if you are growing Streptocarpus with red flowers avoid hard water.
We prefer to use a fertilizer with every watering, but in small doses. The rate is of 1 gram of dry fertilizer to at 3-10 liters of water, depending on the plant growth rate. Even if you water occasionally never exceed concentration 1g per 1 liter.
There is one more universal rule about fertilizers.
The more fertilizer is in the soil the less roots mass plant will grow. Therefore, it is undesirable to fertilize newly transplanted plants, plant’s rosettes without roots as well as plants with weak root system.
It is easy to force your plant to generate healthy root system in the poor substratum. In order to have enough root surfaces the plant will spread its roots through entire volume of your pot. Higher concentrations of fertilizer can be added when the roots have already spread throughout the entire pot. To monitor the progress you can carefully remove the plant from the pot and inspect the roots system. If roots are week and do not cover entire soil volume, fertilization is not desirable. If you start to fertilize the plants before the good root system developed fertilizer will accumulate in the parts of the substratum that do not have roots which in turn will promote degradation of the soil in these area which is not desirable for Streptocarpus. As a result Streptocarpus needs to be repotted. Therefore, we can write another rule:It is better to underfeed than overfeed you plants.