This mound would be best to be built with a porous material such as sand or a mixture of gravel and top soil. When actually planting the lilac it is then that one should add the rich organic soil around the root system. But peat moss is the worst material to add to the planting mix, because it holds moisture and is acidic. The best fertilizer is one that has the second number in it s composition at least twice as high as the first. This will encourage bloom and not push the foliage too hard.
Fertilizers are different from each company so it is difficult to give an exact number.
The fertilizer should be applied at the base of the plant in early spring to help the plant requirements for the year coming. Buds are set the year previous so the fertilizer will work on this year s leaves but next year s bloom. Mulching lilacs is also important. Using mulch helps reduce the heat stress lilacs have in the summer and will hold water better for them during the summer. Lilacs need regular watering during the summer also.