Types of Potash Fertilizer
There are four main types of potassium fertilizers, however only two of them are usually considered for garden use.
- Muriate of Potash - the most popular and economical variety of potash fertilizer.
- Sulfate of Potash - often used on crops susceptible to fertilizer burn because of its lower salt index.
- Potassium magnesium sulfate - although used in many complete fertilizer products, it is less soluble than other forms.
- Potassium nitrate - due to its high cost, this is mainly used commercially for chloride sensitive crops.
Muriate of Potash (Potassium chloride)
Potassium chloride is the chemical name for Muriate of Potash and is an all-purpose fertilizer specifically used for chloride tolerant crops. It contains about 50 to 60% of potash and is the most common form of potash found in fertilizers, being used in around 95% of all products.
It's often applied to medium and heavy soils during the autumn period and because it also comes in granulated form, it can be easily administered and has a high spreading quality. It's also thought to reinforce plant cell walls and as the water inside reaches freezing point, the stronger cell wall resists rupture and the plant can survive without being badly affected.
However, in certain situations where the soil already has a high chloride content, it is thought that it may be harmful to the good bacteria in the soil, so some gardeners believe Sulfate of Potash is preferable in those cases.
Sulfate of Potash (Potassium sulfate)
Being readily soluble in water and of a lower salt index, Potassium sulfate does not contain chloride and is recommended for use on sensitive crops, especially so for the root area. In its basic form it is a white crystilline salt, although it will usually already be in liquid form in off-the-shelf potash fertilizer products. Although the potassium content is generally lower than Muriate of Potash at around 40%, usually Potassium sulfate is more expensive than Muriate of Potash and so is only used when conditions demand it.