N=Nitrogen P=Phosphorus K=Potassium
The 'Bloom Booster' mentioned is of the correct ratio. Miracle-Gro Bloom Booster which I use is 15-30-15 although I once found some with numbers much higher. I recommend it due to the micro-nutrients necessary for healthy plants. It can be mixed with other fertilizer formulations for a custom blend. I like to add a couple of tablespoons of Epsom Salts for additional magnesium.
I never use a foliage sprayer on peonies because the always develop black spotting. I use a leaky bucket to apply the fertilizer directly to the soil around the crown. The Miracle-Gro and magnesium are water soluble.
