Crushed Granite Alternatives for a Gritty Mix

Sand

• Sand is the finest-grade material to mix with potting soil to improve drainage, but not every kind of sand works well to make a gritty mix. Look for the word “coarse” or “sharp” on the sand's package, or buy horticultural sand at a plant nursery. Coarse builder’s sand and sandblasting sand are two kinds of sand that work well while sand from a beach is not recommended due to its fine grade and saltiness.

Pumice

• Pumice forms when tiny gas bubbles are trapped in volcanic lava before it cools, creating a naturally lightweight rock. It is considered a good choice to use in cacti and carnivorous plants' soil medium because water flows around and through the pumice, leading to very fast drainage. Pumice also can be used to offset the weight of tall plants. It is available in four sizes, or grades, and is usually pale gray or pale yellow. It is sterile and weed-free. Rinse pumice to remove dust and fine particles before using it.

Perlite

• Perlite forms when siliceous rock is heated and cooled by Earth’s volcanic forces. It is mined and then processed with intense heat to make it pop like popcorn, expanding it up to 20 times its original volume; it weighs as little as 2 pounds per 1 cubic foot. It is porous and chemically inert, providing no nutrients to plant roots but ensuring drainage. Growers often root plant cuttings in pure perlite or pumice. Perlite dries quickly and wicks water from the bottom of plant pots.

Vermiculite

• Vermiculite, a kind of clay silicate, is composed of a series of thin, parallel planes. When processed under high heat, it expands up to 20 times its original thickness and becomes pleated. The pleats cause vermiculite to retain water when it is included in growing media. Vermiculite contains nutrients, such as potassium, iron, calcium and magnesium, which are released to plants. Vermiculite allows air to flow around it, but it holds water and then releases it. It’s an option for starting seedlings because it aids drainage and helps keep moisture levels even.