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The pros and cons of bonemeal

Q: I’ve heard that bonemeal fertilizer isn’t as effective as it once was. Is it still worth the cost and effort to use?

Linda Terrasi, Newburgh, NY

Bonemeal is organic fertilizer that is high in phosphates. Photo/Illustration: Melissa Lucas

A: Dick Bir, a retured horticulture specialist with North Carolina State University, responds: It’s true. Today’s bonemeal is not the bonemeal of my youth. It continues to be made from animal bones that are steamed, then ground. But more efficient processing methods remove much of the nutrient value, so it can’t be counted on as a complete fertilizer source. Nonetheless, it still is a good source of phosphorus, which helps with cell and seed formation, cell division, and root growth in plants. A soil test will tell you if you need additional phosphorus.

Depending on the brand, bonemeal contains phosphates (P2O5) in amounts ranging from 10 percent to 13 percent. (On fertilizer packages, phosphorus [P] is the second element listed in the series of three, with nitrogen [N] coming first and potassium [K] coming last.) Some brands of bonemeal also contain up to 4 percent nitrogen.

A natural organic fertilizer, bonemeal generally is recommended for bulbs and roses but can be used in just about any situation where a controlled-release form of phosphorus is needed. Because the nutrients from bonemeal and other slow-release fertilizers are insoluble in water, they must be converted to a form that plants can use. This takes time, so you shouldn’t expect an immediate response when using bonemeal.

Other sources of organic phosphorus include rock phosphates and colloidal phosphates. Both are relatively expensive and can be difficult to find. If you can find rock phosphates that list on the packaging a guaranteed analysis of the nutrient content, then using these according to directions is fine. I do not recommend using colloidal phosphates because their fine particles make them difficult to apply.

Cheaper synthetic alternatives offer high levels of phosphorus that are more immediately available to plants. However, super phosphates (0–20–0) and treble super phosphates (0–46–0) are made by treating minerals with acid and aren’t considered natural or organic.

Bulb Booster, a complete fertilizer (9–9–6) with some controlled-release forms of essential nutrients, is another alternative. This may be the most economical way to go when fertilizing bulbs because you would only need to apply one fertilizer once a year.

From Fine Gardening 107, pp. 76