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What Is the White Stuff in Potting Soil?
What Is the White Stuff in Potting Soil?. Potting soil (fresh from its packaging) is a combination of organic materials and soil that also may include perlite, compost, bark, vermiculite, peat or sphagnum moss, sand, or water-retention crystals. Perlite and vermiculite are the white particles or pebble-like bits in the mix.
Potting soil (fresh from its packaging) is a combination of organic materials and soil that also may include perlite, compost, bark, vermiculite, peat or sphagnum moss, sand, or water-retention crystals. Perlite and vermiculite are the white particles or pebble-like bits in the mix.
Perlite
When volcanic rock is heated to 1,800 degrees Fahrenheit, it creates a porous, lightweight, sterile material called perlite. Perlite is used in potting soil to lighten the soil and provide better drainage. It does not hold moisture or nutrients well and has a near-neutral pH of 7 to 7.5.
Vermiculite
Mica heated to 1,800 degrees Fahrenheit becomes vermiculite. In potting mixes, it helps retain moisture and nutrients, and helps to aerate the soil. It is extremely lightweight, has a pH of 6.5 to 7.2, and contains plant-accessible traces of calcium, magnesium and potassium.
Considerations
If you decide you want a lighter mix by adding perlite or vermiculite, keep the plant's needs in mind. Xeric, succulent or desert plants would prefer perlite for better drainage, while water and nutrient-hungry plants would benefit from vermiculite. Don't go overboard on perlite: it can cause fluoride burn in the leaves of some plants.
