"Nursery, can you get the good taste from backyard organic fertilizers such as manure or do you need SOP?"
In most cases organic fertilizers will do the job but it needs to be a balance of different organic fertilisers. Usually SOP give additional benefits, notably with citrus. Take cow or horse manure where the dung only is collected whereas with poultry the droppings also contain the urine. Again with horses there is a difference with stable manure including straw as against manure collected from the paddock. Bear in mind that a lot potash is passed through in the liquid but a percentage is also in the straw. Also a green manure crop returned to the soil returns all potassium and in a slow release form.
Sometimes organic farming needs a little help. Crop yield and the ability to get healthy plants capable of dealing with pests and variable weather as well as flavour are important.
I'm sure that any stable manure from Black Caviar gave plants a racing start.
