Fertilizing bulbs

Although newly planted bulbs have all the stored foods they need to perform the following spring, annual fertilizing can help keep this show going year after year.

A general-purpose fertilizer works fine for bulbs. A higher phosphorus content is often recommended simply because it inspires root growth as well as flower production. So go ahead and use the 5-10-5 or something close to this ratio.

People often recommend bone meal for bulbs, with its approximate formulation of 2.5-24-0. Alas, modern-day, store-bought bone meal is highly sanitized, and its benefits are questionable. Nonetheless, some bulb enthusiasts swear by it. This natural material tends to be very slow to release it nutrients, so some gardeners prefer using super phosphate instead; this material is rock phosphate that has been treated with sulfuric acid to make it more soluble. It's 20 percent phosphorous (0-20-0).

Some people debate over where to place the fertilizer. In the hole? On the soil surface (top-dressing)? The case for adding plant food to the planting hole is that it's right at the roots, where plants need it (some people are concerned that direct contact with fertilizer will burn a bulb or its roots, but not all bulbs are so fragile). The case for soil-surface feeding is that the nutrition can filter into the growing area more gradually.

What to do? Try whichever way is more convenient for you, and judge the results. You can always switch methods.

You need to fertilize only once, and you have three opportunities to do so:

  • At planting time (usually in the fall): I describe this option in the previous "How to plant bulbs" section. Fertilizing at planting time gets the bulbs off to a good start.
  • As growth starts, usually in early spring: This fertilizing improves the current season's display. Individual plants will be more robust, with brighter, longer-lasting blooms.
  • Post-bloom: While the foliage dies down naturally, this little boost sends food down to the bulb to fuel next year's show.

The standard application rate for fertilizer is a tablespoon or small handful per square foot, but read the label on the fertilizer package for exact directions. Always apply fertilizer to damp ground, and water it in afterwards if there's no rain so it penetrates the soil and gets to the root zone.

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