Saltpeter, also known as nitrate of potash and potassium nitrate, is used for a wide range of applications in gardening. It contains potassium and nitrogen. Saltpeter, which has the chemical symbol KNO3, can be used to quicken germination of certain seeds, as a fertilizer, to encourage plants to flower and fruit, and to remove tree stumps. People are restricted from purchasing large amounts of saltpeter because it also can be used as an explosive.
Soaking in a saltpeter-water solution can speed the germination of seeds with a hard outer coat, according to the National Gardening Association's website. The method also can be used for very old, dry seeds and when the temperature is on the low side. Saltpeter speeds a seed's germination because it simulates the digestive process, breaking down the seed's hard outer coating and allowing the inner portion to absorb water, nutrients and light better.
Saltpeter can be used as a fertilizer to increase the nutritional intake of a plant. It can be applied directly to the soil as a fertilizer, or it can be used as a spray. As a spray, it is applied directly to plant foliage. The amount required and the application frequency varies with the type of plant. Foliar application — rather than application to soil — is useful when plant roots are damaged, when the soil is too wet and when the plant requires more nutrition than it can take in through its root system alone.
The nitrogen and potassium in saltpeter cause plants to blossom and set fruit more quickly than they would otherwise. The potassium encourages a plant's early growth, improves its water use efficiency, boosts its ability to tolerate diseases and increases its protein production. Because potassium also helps with the transfer of nutrients between cells and cell walls, it aids with the production of fruits and flowers. The nitrogen in saltpeter encourages foliage production; nitrogen is essential for plant growth and photosynthesis. The increased photosynthesis that results from the nitrogen also encourages fruit and flower production because the plant has more available energy.
Saltpeter is used to remove a tree stump in two ways: by speeding the stump's rotting process and by burning it. Both methods require drilling large holes into the stump and filling the holes with saltpeter. If you want to use the saltpeter method that quickens the stump’s decomposition, then add water to the saltpeter in the holes, and let the saltpeter-water solution remain in the holes. If you want to use the faster method, light the dry saltpeter in the holes on fire. That method causes the saltpeter to burn through the roots, destroying the stump's above- and below-ground portions. When using saltpeter to burn a stump, ensure all other flammable materials are well away from the area, and have water or a fire extinguisher ready for use in case it is needed to put out the fire.
- National Gardening Association: Starting Seeds Soaking in Saltpeter Solution
- Potassium Nitrate Association: Foliar Applications of Potassium Nitrate
- Highlights of Agricultural Research: Getting to the Nitrogen Source of the Problem
- University of Minnesota Extension: Potassium for Crop Production
- The Story of Flowers: The Potassium Myth
- Canadian Gardening: Tree Stumps and Saltpeter
- Organic Gardening: Nitrogen -- The Elusive Nutrient