Steps to Fertilizing Tulip Bulbs
1. Dig a hole with a trowel or spade 8-9"* in depth. Sprinkle bonemeal or superphosphate on the soil at the bottom of the hole and mix into the soil well. Never place the bulb directly on the fertilizer as the phosphorous can harm the bulb.
2. Once the plant material breaks the surface of the soil you can begin fertilizing normally once per month. Use a bulb fertilizer such as a 10-10-10 mixture according to package instructions. For optimal results, add bonemeal at a ratio of two cups per ten square feet.
3. Stop fertilizing when bulbs begin to flower as this encourages bulb rot and a shorter bloom time.
Optimal pH Range for Tulip Bulbs
The exact proportion of fertilizer that is best for your tulips will depend on the pH of your soil. Tulips thrive best in soil with a pH balance between 6-7, which is slightly alkaline. If your soil falls below or above this range you can easily modify it with the addition of soil amendments.
Tulip bulbs do not like clay soil but may still be planted as long as the soil is amended with a generous amount of peat moss, compost, or additional organic matter as needed.
The depth of the planting hole will depend on the size of the bulb. As a general rule of thumb the hole should be twice the depth as the height of the bulb. A smaller bulb would be planted less deeply than a larger bulb.