What type of fertilizer does my Bigleaf hydrangea need?

To promote flowering, you need to adjust your fertilization strategy in late spring by using some fertilizers with higher phosphorus content. For blue Bigleaf hydrangea cultivars, use a fertilizer with a nutrient ratio of 8-4-8 or something similar that has a lower phosphorus content. Other Bigleaf hydrangea cultivars can be fertilized with any type of all-purpose fertilizer with a balanced nutrient ratio, such as 10-10-10. To lower the pH and make the soil more acidic for blue coloration, add small amounts of either an aluminum sulphate fertilizer or wettable sulphur to the soil and mix in well. High pH soil will turn blue flowers pink or red. To raise the pH, apply a liberal amount of limestone to the soil and mix it in well. Too much of either type of compound can injure your Bigleaf hydrangea, so it's better to add too little than too much.