Organic Sources of Potassium for Your Lawn or Garden

Lawn and Garden, Soil & Fertilizer by Julie Day


Hardwood ashes are a popular “home-made” source of potassium.

Potassium is a very important nutrient for overall plant health. It’s involved in protein synthesis and in the flow of nutrients and water up and down the plant. Potassium strengthens plants against cold, heat, disease, and pests, and it’s the key ingredient in fertilizers labeled as “winterizers.”

If you’re looking to go organic, there are many ways to supplement your lawn or garden with potassium without using chemical fertilizers. Here are the most common sources of organic potassium:

  • Compost: Compost is full of nutrients, including potassium, especially if it is beefed up with banana peels and other fruit and vegetable waste. The potassium compounds in compost are water-soluble, which makes them readily available to plants but also likely to leach out of your compost pile over time.

  • Wood Ash: The original source of “potash” fertilizers, hardwood ashes can be used directly as a fertilizer (about a 5-gallon bucket per 1000 square feet) or added to your compost pile to increase the potassium content. Wood ash also raises soil pH, so be sure to do regular soil testing to make sure it stays balanced.
  • Kelp Meal: Available dried or liquid, kelp and seaweed offer potassium to the soil in a fairly quick-release form.
  • Greensand: Mined from ancient former sea beds and is rich in a number of minerals including potassium. It’s used both as a fertilizer and a soil conditioner, or it can be mixed with compost.
  • Muriate of Potash (potassium chloride): Mined from ancient deposits, this commercially available product can be used as natural sources of potassium, though the chlorine found in it can harm soil microbes.
  • Sulfate of Potash (potassium sulfate): More expensive than muriate of potash but safer, since it doesn’t contain chlorine. Not all potash products are considered organic, so make sure the product you use is approved by the Organic Materials Review Institute (OMRI).
  • Sul-Po-Mag: A variation of potash, Sul-Po-Mag is actually a naturally-occurring mineral called langbeinite (sulfate of potash-magnesia). Sul-Po-Mag is water soluble and convenient, although it shouldn’t be used unless your soil also needs sulfur and/or magnesium.
  • Granite Dust: Available from granite quarries, granite dust is a relatively inexpensive way to add potassium and tract minerals to your soil. Since it’s ground-up rock, this product is very slow to release its minerals and is not a quick fix.

Further Information