Answer: I think you mean a potting soil for ericaceous plants, or members of the heath family (Ericaceae). These plants generally need an evenly moist yet well drained soil with an acid pH and ample air space. A possible recipe would be this variation of John Innes Base mix #1: 7 parts sterilized loam, 3 parts peat, 2 parts sand or grit, 4 oz fertilizer per 8 gallons of mix.
Another possibility would be Cornell Soil-less Mix (also omitting the limestone):1/2 cubic yard milled spagnum peat moss, 1/2 cubic yard vermiculite, 1 pound superphosphate, 2 pounds 5-10-5- fertilizer. For a heavier mix you might use 1 part peat moss, 1 part composted bark, and 1 part sand instead of half peat moss and half vermiculite.
You may also find pre-blended potting soils and soilless mixes especially formulated for acid-loving plants if you check with larger garden centers or nurseries.
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