Potassium sulphate, also called sulphate of potash or SOP, is a naturally mined mineral fertilizer that supplies two nutrients at once: potassium and sulphur, with low chloride. This grade is a fine pink powder guaranteed at 0-0-53 with 18% sulphur, mined and solar-evaporated from natural brine deposits in Saskatchewan, Canada.
Because sulphate of potash carries low chloride and has a low salt index, it suits situations where chloride-sensitive crops or salt-prone soils rule out muriate of potash (0-0-60). Growers use it at every scale, from raised beds and containers to market gardens, orchards, vineyards, and broadacre fields.
What potassium and sulphur do
Potassium (K): drives water regulation, enzyme activation, photosynthesis, and the movement of sugars and starches into fruit, tubers, and storage tissue. Adequate potassium supports fruit size and quality, along with the plant's own tolerance of drought, cold, and general stress.
Sulphur (S): a building block of proteins, enzymes, and chlorophyll, and a driver of how efficiently the plant turns nitrogen into growth. Good sulphur nutrition supports deep green colour, strong protein and oil formation, and in alliums and brassicas, the sulphur compounds behind their flavour and pungency. Because it is supplied as sulphate, the form roots take up directly, it goes to work without needing to be converted in the soil.
Low Chloride, low salt index: sulphate of potash delivers potassium with very little chloride (<0.1%) and carries a lower salt index than most potassium sources. That makes it a safer fit for chloride-sensitive crops such as potatoes, tomatoes, grapes, and berries, and for soils where salt build-up is a concern.
Who it's for
Home gardens and raised beds: correct potassium shortfalls ahead of flowering and fruiting.
Containers, greenhouse, and indoor: measured potassium and sulphur without the chloride build-up that closed root zones are prone to.
Market gardens: low chloride potassium for quality-sensitive vegetables and small fruit.
Orchards and vineyards: potassium for fruit fill and quality, well suited to chloride-sensitive vines and trees.
Broadacre and field crops: soil-test-driven potassium and sulphur correction.
Turf: potassium for stress and wear tolerance without a heavy salt load.
Commercial cannabis: potassium and sulphur through late vegetative growth and flower.
How to use
Start with a soil test. Potassium is easy to overdo, and excess potassium interferes with magnesium and calcium uptake, so match the rate to a recent test rather than applying by habit. Apply to moist soil and water in; sulphate of potash dissolves more slowly than chloride salts, so it needs moisture to become available.
Soil incorporation (beds and new plantings). Rates per 1,000 sq ft (100 m² in brackets). Apply based on a current soil test.
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Light maintenance: 1-2 lb (0.5-1.0 kg)
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General corrective: 3-5 lb (1.5-2.4 kg)
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Known deficiency: 6-10 lb (2.9-4.9 kg); split into two applications 4-6 weeks apart
Incorporate to 10-15 cm (4-6 in) and water in. Supplies 17-18% sulphur as sulphate; account for this where soil sulphate is already adequate.
Top-dress (established plants and trees). 0.25 kg (0.5 lb) per 2.5 cm (1 in) of trunk diameter measured at 1.4 m (4.5 ft). Spread evenly in a band from mid-canopy outward past the dripline, scratch into the surface and water in thoroughly.
Dissolved feed (watering can or small tank) Mix 0.5g to 2g of product per litre of water (2 to 7.5 g per US gallon). Use the lower end for regular feeding and the upper end for occasional corrective drenches. Stir until fully dissolved, then apply to the root zone at 4 L per 1 m² of bed area (about 1 US gallon per 10 sq ft), or 500 mL (about 2 cups) per established plant. Do not exceed 2 g per litre.
Rate reference, approximate nutrient concentrations at common stock-solution rates:
0.5 g/L (1.9 g per US gallon): 220 ppm K, 88 ppm S, ~0.75 mS/cm
1.0 g/L (3.8 g per US gallon): 440 ppm K, 175 ppm S, ~1.5 mS/cm
1.5 g/L (5.7 g per US gallon): 660 ppm K, 265 ppm S, ~2.2 mS/cm
2.0 g/L (7.6 g per US gallon): 880 ppm K, 350 ppm S, ~3.0 mS/cm
EC added is on top of your base water and nutrient solution.
Fertigation and irrigation: this is a fine powder grade, not a fully soluble grade, so it works in some injection setups but not all. It suits systems that tolerate a little sediment, such as larger-orifice emitters, sprinklers, hand or batch injection, and hose-end feeding. Sulphate of potash is only moderately soluble, about 120 g/L in water at room temperature, so mix well below that and use warm or hot water, which dissolves it faster and lets you get more into solution (solubility roughly doubles near boiling). Pre-dissolve fully, keep the stock tank agitated, let undissolved fines settle, and filter before the lines; keep the mix well under saturation, since a saturated solution can drop crystals back out as it cools. It's a poor fit for fine drip and micro-jet emitters, where its natural insolubles and slow dissolving can clog heads over time. Keep it in its own stock tank rather than mixing it concentrated with calcium sources, which can cause precipitation. Where you need clean metering through fine emitters, the fully soluble solution grade is the better tool, though note it is made by a synthetic process that isn't permitted for organic production.
Field, orchard, and vineyard: where a soil test shows potassium deficiency, common rates run 200 to 500 lb of product per acre (about 225 to 560 kg/ha), split across the season as needed. For operations working at this scale, we also carry this in a 1000 kg pallet (40 × 25 kg): see Potassium Sulphate 0-0-53 1000 kg.
Powder vs solution grade
We carry two forms of potassium sulphate, and the difference matters for organic growers. This powder is a naturally mined, solar-evaporated mineral, which is why it is approved for use in organic production. Our Potassium Sulphate Solution Grade is a fine, high-purity crystal that dissolves cleanly for fertigation and foliar feeding, but it is made by a synthetic process (the Mannheim process, which reacts potassium chloride with sulphuric acid), and that production route is not permitted under organic certification. It's the same nutrient reaching the plant either way; what differs is how each is made. Choose the mined powder for certified-organic programs, and the solution grade where clean solubility through fine emitters matters more than organic status.
Guaranteed analysis and specifications
Guaranteed analysis:
Soluble Potash (K₂O) 53%,
Elemental (K) 44%
Sulphur (S) 18%.
Chloride: under 0.1% (effectively chloride-free).
Form: fine pink powder.
Reaction: mildly alkaline in solution (about pH 8), but close to neutral in its effect on soil; it does not raise soil pH the way a liming material does.
Storage and handling
Keep dry and sealed. The crystals are anhydrous and store indefinitely in dry conditions. Keep out of reach of children and pets, avoid eye contact, and wash hands after handling.
Potassium Sulphate powder is a permitted substance for organic crop production under Canada's organic standards, CAN/CGSB-32.310-2026 and CAN/CGSB-32.311-2026, as a soil amendment.
