I assume these were potted plants which means the root systems will be drawing most nourishment from the potting mix, at least for this season. Nurseries often include slow release Osmocote in their pottin mix so plants can go months without supplementary fertilizer. You need to ask the nursery or othere source. Osmocote is easy to see in the mix- tiny balls of several colors.

If the plants were bare-root, supplementary fertilizer might not be necessary, but for your plants (once again assuming you bought them rooted in potting medium) some kind of acidic fertilizer formula may be helpful and even necessary. Just follow the directions for fertilizing a potted plant on the label.

I have been using MiracleGrow-acidic formula, one tablespoon per 4 gallons of water. I wait until the shrub could use some water, between rainstorms. For established shrubs, I apply this in early April, when the leaves are just beginning to emerge, and again in May. Since we have many shrubs that are heavily covered in fruit this year, I might apply one more time, in early June. This year, I am using Schultz's plant food, for acid loving plants, because I couldn't find Miracle Grow. It has a very similar formula. There is an advantage to using a comprehensive plant food on blueberry shrubs, rather than a single element fertilizer such as ammonium sulfate. If the plant has a problem, such as iron chlorosis(yellow leaves) or red/brown leaves, and I know that I have applied a multi-element comprehensive fertilizer, I can be reasonably certain that the soil has high pH, which interferes with nutrient absorption by the roots. The solution, in this case, is to lower soil pH, not apply more fertilizer. Typically, these issues appear in the spring, and this year was no exception with our blueberry shrubs. If your water and soil do not have limestone or dissolved limestone present, you will likely not have problems with high soil pH.