The best strategy to fertilize Haworthias is to supply a continual low concentration in every watering with proper flushing. By linking nutrient supply with water supply, a plant always gets adequate nutrients in proportion to the water uptake, regardless of its size and the activeness of growth. In addition, some micronutrients (e.g. Calcium and Silicon) are not mobile in a plant, so must be in the nutrient stream at all times to be effective.
Synthetic fertilizers are better choices than organic fertilizers. Most synthetic fertilizers are soluble in water and available for immediate uptake. This allows the nutrient supply to be accurately controlled. In contrast, organic fertilizers need to be decomposed before being usable by plants, and the decomposition process can be affected by many environmental factors (for example, moisture, pH, and temperature) and hence unstable.
Besides the basic nitrogen, phosphorus, and phosphorus (NPK), Haworthias also need various micronutrient for optimal growth. An unbalanced nutrient availability can lead to deficiency and even toxicity problems. Giving Nitrogen the value of 100, the ideal supplement ratio of essential elements are listed below as a weight percentage of N.
|Element||Ideal Range||Optimal Value|
Completing the above list may need to mix several fertilizers. As the base, use a NPK fertilizer with N:P:K ratio in 3:1:2 (for example the ones with NPK rating 24-8-16, 12-4-8, 9-3-6), because its actual NPK elements are the closest to the above 100:16:62 ratio (how to calculate). Avoid fertilizers that contain urea, because the conversion of urea to nitrogen usable by plants are slow under low pH, which is preferred by Haworthias.
If tap water is used, check the water quality report or get the water analyzed in a laboratory. The water may already have some elements (often Ca and Mg) well represented.
Add Silicon to the Fertilizer Program
Silicon is not considered as an essential element, but experiments have shown that it improves plant growth, increases the tolerance to temperature extremes and drought, and also protects plants against pathogens and insects by making their cell walls stronger.
Using N as 100, the ideal weight ratio of Silicon (Si) is ~86.
For Haworthias, the ideal concentration of nitrogen in water solution is ~0.003%, while other elements follow the above ratios accordingly. When diluting fertilizers, one fertilizer should be fully diluted in water before adding another, otherwise, there can be undesired chemical reactions among concentrated fertilizers.
The acidity of the nutrient solution is a major determinant of balanced nutrient uptake. The ideal pH range is 5.0~5.5 (5.2 optimal). Tap water is often alkaline, and most likely fertilizers also affect pH. After diluting all fertilizers, use a pH meter to test the solution and apply pH adjustors until the pH is in the ideal range. Hydrochloric acid is the best acidifier for lowering pH, as other acidifiers often result in chemical by-products which negatively affect the plant growth.