Are you buying a large bag of fert from home depot for $45?
Do you buy from a mom and pop garden center and you get that bag at a 10% discount?
Do you buy from a commercial/wholesale dealer for $25?
Paying retail can't markup unless you charge too little for your labor.
How can you mark up more then the 10% discount you get from the garden center? Can't.
I buy from wholesaler, I charge fert cost plus $10 to cover time to get the material. Then my labor has always been the same rate as mowing. Yes that means the $45 box store bag I charge my customers $35 + my labor. Never give fert and labor pricing. Give on inclusive price. They don't need to know how much labor vs material.
My prices for fert are competitive.