The optimal soil pH for daffodils is 6-7.
What is pH?
The pH scale ranges from 0-14 with 7 being neutral. A pH soil level ranging between 7-0 means that the soil contains more acid the lower the number progresses. A pH soil level ranging between 7-14 means the soil has a higher alkaline content the higher the number progresses.
The pH level of soil affects the solubility of the soil’s nutrients and some plants cannot thrive in a soil that is too acidic or too alkaline. In these cases, the soil needs to be amended to meet the needs of the particular plant.
How to Raise pH
You can raise the pH of your soil, or make it more alkaline, by adding materials such as wood ash, hydrated lime, or limestone. In order to raise the pH to 6-7 for daffodils you will need to amend the soil based on a soil test and the current pH level and add a proportionate amount of limestone. For example, if the soil pH is 5, you will need to add 8 lbs of limestone per 100 square feet.
How to Lower pH
You can lower the pH of your soil, or make it more acidic, by adding materials such as organic mulch, sphagnum peat, sulfur, aluminum sulfate, iron sulfate, or acidifying nitrogen. For smaller beds, the most efficient soil amendment is sphagnum peat. Work in a 2″ layer to the top 12″ of soil.
For larger areas, sulfur is more cost efficient but slower acting. In order to lower your pH to 6-7 for daffodils you will need to test the soil to know your exact pH and then add a proportionate amount of sulfur. For example, if your soil has a pH of 8, in order to lower it to 6-7 you need to add .3 lbs. of sulfur per 10 square feet.