Cottonseed meal is a byproduct of the cotton industry. In the cotton making process, each boll has to be removed of its seeds; the leftover cottonseed is pressed for cottonseed oil which is used as a cheap cooking oil. The meal left over from oil production is dried and used as animal food or fertilizer.
Cottonseed meal is an excellent fertilizer, especially as a nitrogen source for acid-loving, fertilizer sensitive plants such as rhododendrons and kalmias. Cottonseed meal has a 6-2-1 NPK ratio (Nitrogen-Phosphorus-Potassium), making it a great main-season nitrogen source. Because cottonseed meal is an organic fertilizer, the nitrogen is slowly released over the season as the meal is broken down by soil microbes. As a plant-based product, cottonseed meal has a host of necessary micronutrients. Cottonseed meal also tends to be a soil acidifier, as it is mostly organic matter - This greatly enriches the soil and helps beneficial soil fungi flourish.
Cottonseed meal is an easy-to-spread, dry granular fertilizer. While it is almost impossible to burn plants with cottonseed meal, it is still best to follow recommended rates of application.
For rhododendrons, azaleas and other acid-loving shrubs, cut the application rate in half. These doses are best applied in two applications, one in early spring just before leaf-out, and another in early summer but no later than July 1st.