Spring-blooming bulbs are almost always planted in autumn. After a long winter slumber, the bulbs awaken and quickly switch to rapid growth mode, producing long green stems that explode into dramatically colored blossoms almost overnight. For many spring bulbs, all this occurs within a narrow two week time frame. Most of the time our bulbs produce wonderfully every year, so we assume that there are enough nutrients in the soil to support this massive expediture of energy each season.
It’s important to know those big fat bulbs represent all the energy and food the plants have stored up for next season’s bloom. When you first plant spring-blooming bulbs, the only thing they need to do that winter is to send down some new roots. To help the bulbs do this, you feed newly planted bulbs with a balanced fertilizer that has a good dose of phosphorous in it. That’s what “Bulb Food” is and why bonemeal is often recommended. Bonemeal used to be the recommended way to feed flowering bulbs, but current meat processing procedures tend to reduce the amount of phosphorus remaining in the bones, so a bulb food is not preferred. Phosphorous isn’t good at working its way down through layers of soil. To be effective, it needs to be added to the planting hole or worked into the surrounding soil, rather than just sprinkled on top.
After that, the experts tend to disagree. Some favor top dressing with fertilizer each fall. Others recommend an early spring feeding and still others say not to do anything until the flowers have faded. Some supplemental spring feeding makes sense for flowering bulbs, especially if you use a slow-release fertilizer. Although the bulbs are using their reserves for food, they are expending a lot of energy and will be pulling nutrients from the soil. It is recommended you fertilizer early rather than waiting until after the blooms have faded because spring-flowering bulbs have such a short growing season and you will want to make sure the fertilizer is accessible in time and that the plant has the opportunity to grow and store energy for as long as it can.
One last thing to keep in mind is that most spring-blooming bulbs prefer a soil pH between 6.0 and 7.0. This is the pH range in which the bulbs can access the most nutrients from the soil. Test and amend your soil if your bulbs are struggling, despite your best efforts at feeding them.
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