Potassium is the “quality nutrient”. It decides how large, sweet, firm and long-lasting your fruit will be — which is why the fruit-fill stage is when growers reach for potash. Three water-soluble options dominate fertigation programmes: sulphate of potash (SOP 0-0-50), potassium nitrate (13-0-45) and potassium schoenite. Here is how they compare.
Key takeaways
- All three supply potassium in a soluble form with low or no chloride, making them suitable for sensitive and high-value crops.
- Potassium nitrate adds quick-acting nitrate nitrogen; SOP adds sulphur; schoenite adds magnesium and sulphur.
- Choose based on what else your crop needs at that stage, your water quality, and your budget.
Why potassium matters
Potassium controls how plants open and close their stomata, move water and transport sugars into fruit. Adequate potash improves fruit size, colour, sugar content (Brix), firmness and post-harvest life, and helps crops tolerate heat, drought and disease pressure. Demand for potassium peaks from flowering through fruit fill, which is exactly when a soluble source pays off.
Sulphate of Potash (SOP) 0-0-50
Water-soluble SOP supplies about 50% K₂O together with sulphur, and is very low in chloride. Sulphur supports protein formation and flavour compounds, which makes SOP popular for onions, garlic, brassicas, grapes and fruit trees. Because it adds no nitrogen, SOP is useful late in the season when you want to finish fruit without encouraging extra leafy growth.
Potassium Nitrate 13-0-45
Potassium nitrate combines roughly 45% K₂O with 13% nitrogen in the nitrate form, which plants take up quickly. It is one of the most widely used fertigation and foliar products for flowering and fruit development, especially where the crop still needs some nitrogen. It dissolves easily and is suitable for greenhouse, open-field and orchard programmes.
Potassium Schoenite
Potassium schoenite is a natural double salt of potassium sulphate and magnesium sulphate. It delivers potassium, magnesium and sulphur in a single chloride-free product. Magnesium is the centre of the chlorophyll molecule, so schoenite is a smart choice where magnesium deficiency (yellowing between leaf veins) is common, such as in sandy, leached or high-potash soils.
Side-by-side comparison
| SOP 0-0-50 | Potassium Nitrate 13-0-45 | Potassium Schoenite | |
|---|---|---|---|
| Potassium | High (50% K₂O) | High (45% K₂O) | Moderate |
| Companion nutrient | Sulphur | Nitrate nitrogen | Magnesium + sulphur |
| Chloride | Low | Low | Chloride-free |
| Best timing | Fruit maturity, finishing | Flowering to fruit fill | Fruit development |
| Ideal for | Onion, garlic, grapes, orchards | Vegetables, fruits, flowers | Mg-deficient soils, sensitive crops |
How to choose
- Crop still needs nitrogen? Choose potassium nitrate 13-0-45.
- Want to finish fruit without extra leaf growth, or need sulphur? Choose SOP 0-0-50.
- Seeing magnesium deficiency? Choose potassium schoenite, or combine it with another potash source.
- Mixing in one tank? Keep sulphate products away from calcium products to avoid gypsum deposits in drip lines. Our fertigation guide covers tank separation in more detail.
Supply from Mitra Eco Exports
We export all three potash fertilizers in moisture-proof 25 kg bags, with private-label packaging available and a batch Certificate of Analysis with every consignment. Combine them with our NPK grades and calcium liquids in a single shipment.
Need a quotation?
Tell us the product, quantity and destination port. Our export desk replies within 24 hours with pricing, specifications and sample availability.
Frequently asked questions
Is SOP better than potassium nitrate?
Neither is universally better. SOP adds sulphur and no nitrogen, which suits the finishing stage. Potassium nitrate adds quick-acting nitrogen, which suits flowering and early fruit development.
Is potassium schoenite water soluble?
Yes, potassium schoenite is soluble and can be applied through fertigation or as a foliar spray.
Which potash fertilizer is chloride free?
Potassium schoenite is chloride-free, and SOP and potassium nitrate are low in chloride, making all three suitable for chloride-sensitive crops.
What is the minimum order for potash fertilizers?
We welcome trial LCL orders from 2 metric tonnes, and products can be combined in one consignment.
This guide is for general information. Application rates and product choice depend on crop, soil, water quality and local regulations; please consult a qualified agronomist and check registration requirements in your country.