written on Jan 05, 2018 and last revisited on Aug 05, 2018

The best strategy to fertilize Haworthias is to supply a continual low concentration in every watering. By linking nutrient supply with watering, a plant always gets adequate nutrients in proportion to the water uptake, regardless of its size and activeness. Besides, some micronutrients (for example, Calcium and Silicon) are immobile in plant tissues and must be supplied at all times.

Tap water is often alkaline and ideally should be acidified before using.
Tap water is often alkaline and ideally should be acidified before using.

Fertilizer Choices

Comparing to organic fertilizers, synthetic fertilizers are generally better because most of them 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, and the decomposition process can be affected by many factors (for example, moisture, pH level, and temperature) and therefore unstable.

Besides the basic nitrogen, phosphorus, and phosphorus (NPK), Haworthias also need various micronutrient for optimal growth. Giving Nitrogen the value of 100, below lists the ideal ratio of supplying essential elements, as a weight percentage of N. This ratio is roughly the same ratio found in plant tissues. An unbalanced nutrient availability can lead to deficiency and even toxicity.

ElementIdeal RangeOptimal Value
Nitrogen (N)100
Phosphorus (P)13-1916
Potassium (K)45-8062
Sulfur (S)6-98
Magnesium (Mg)5-1510
Calcium (Ca)5-1510
Iron (Fe)0.7
Manganese (Mn)0.4
Boron (B)0.2
Zinc (Zn)0.06
Copper (Cu)0.03
Chlorine (Cl)0.03
Molybdenum (Mo)0.003

Completing the above list may need to add several fertilizers. As the base, use a fertilizer with N:P:K ratio in 3:1:2 (for example, 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, it is recommended to check the water quality report. The water may already have some elements (often Ca and Mg) well represented.

Adding Silicon Fertilizer

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.

Fertilizer Concentration

For Haworthias, the ideal concentration of nitrogen in a water solution is ~0.003%, and the concentrations of other elements should follow the above ratios accordingly. When adding fertilizers, one fertilizer should be fully diluted in the water before adding another, otherwise, there can be undesired chemical reactions among concentrated fertilizers.

Acidity Adjustment

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). After diluting all fertilizers in water, use a pH meter to test and apply pH adjustors if necessary. Hydrochloric acid is the best acidifier for lowering the pH level because other acidifiers often result in chemical by-products which may have negative effects on plants.