The proper fertilizer diet for fall-planted bulbs

By , Staff writer of The Christian Science Monitor

Like so many things in this world today, bone meal isn't what it used to be. In fact, it has changed so much that it is no longer worth including in the diet of fall-planted bulbs, particularly tulips, according to Paul Nelson, professor of Horticultural Science at North Carolina State University. The reason, he explains, is simple.

In the old days, bone meal contained all the original ingredients, including marrow and some accompanying gristle. As a result, it was rich in both nitrogen (around 6 percent) and phosphorus (12 percent), which is why it was the established fertilizer for spring-flowering bulbs for so long. While modern bone meal remains a good (though expensive) source of phosphate for the garden, it contains less than 2 percent nitrogen, because the bones are first steamed to extract their gelatin.

Dr. Nelson's research on spring-flowering bulbs shows them to be ``one of the most efficient plants in the garden,'' with a low fertilizer requirement and no great need of phosphate. On the other hand, they do benefit from a little additional nitrogen - so Nelson recommends using aged manure or compost and a sprinkling of limestone if soil tests shows the soil is low in calcium. Any phosphate your garden soils might need might just as effectively, and less expensively, come from rock phosphate, though it is slower at releasing its nutrients in the first year.

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Any phosphate should be dug into the soil at planting time, since it moves through the soil at a minuscule rate.

Manure, however, can be applied as a top dressing on established beds or over new plantings. The nitrogen it contains will move into the soil and down to the roots with rainwater.

Nelson recommends feeding in the fall when bulbs develop their first roots, and again in early spring, six to eight weeks before flowering.

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