What Herb Can Be Grown in Decomposed Granite?

What Decomposed Granite Does

• Decomposed granite occurs naturally in mountainous soils, such as that of Colorado. Blended with sand and alkaline soil, soil high in decomposed granite sometimes needs the addition of large amounts of organic materials to improve the soil's nutritional value and water-retaining capacity. Added to heavy clay soils, such as the Blackland soil of Central Texas, for example, decomposed granite allows for better soil drainage, which can prevent delicate roots from drowning. Adding a few trace elements but basically chemically inert, decomposed granite permits the passage of water to plant roots, then past them to drain off (see Resources).

How Decomposed Granite Supports Herbs

• Central Texas gardeners note that the region's prolonged dry heat plus the presence of decomposed granite in sandy, slightly alkaline soil provides hospitality to what cooks might call the Mediterranean herbs: rosemary, oregano, basil and lavender. Both soil and weather conditions in this region of Texas resemble the intense summers and dry ground of Greece, Italy and southern France. Mixing soil with decomposed granite or using the edge of a granite path as a planting space for herbs extends the list to include those herbs most prone to damp-related problems and disease, such as creeping thyme. Roses grown for aroma and healing properties are also reported to do well in soil high in decomposed granite.

Decomposed Granite as Soil Amendment

• In an account of a visit to the Tunicum Herb Barn in Erwinna, Pennsylvania, the Tohickan Garden Club diarist notes the frequent addition of decomposed granite in varying sizes to improve soil drainage. Granite is used in grit sizes from the smallest chicken grit to turkey grit and, notes the writer, is particularly helpful for plants susceptible to root rot.

Large-Scale Plantings

• Lavender farmer Bea Kunz gives great credit to the presence and use of decomposed granite in the soil of her Tennessee lavender farm. All varieties of this popular herb, known like the thymes for root-rot problems and damp-soil diseases, benefit greatly from the drainage decomposed granite can provide.