People think that using organic fertilizer in container gardens is better than chemical fertilizer.
Organic fertilizer like fish emulsion, manure or blood/bone meal needs to be broken down by microbes into nitrogen, phosphorus and other nutrients the plant can utilize. So it's great for use in gardens in the ground to add nutrients back in and amend the soil.
In containers, most of the time the plant isn't in those containers long enough for it to be broken down, or the fertilizer gets washed out while watering. Also a lot of potting mixes are sterilized so little to no microbe action is taking place.
I can't tell this to my customers because many of them are very against chemical fertilizer. But organic fertilizer IS chemicals. It's just not broken down yet in usable form. Customers use these fertilizers and don't see results and just keep adding them...
Just as a side note, I do use both types of fertilizer. But I choose which to use based on the plant and if it's in a container or not. Otherwise you end up with nutrient deficient plants with chlorosis or other undesirable symptoms.