I have potted and trained my two junipers (one blue point and one savin) last month. I just removed the wires on the blue point juniper today. Do I need to fertilize both of them during this growing season? The blue point juniper is very young, maybe a year old. The savin is probably at least two.

You can fertilize as soon as they start growing. However not absolutelly necessary.

Yes, you need to fertilize. Nutrients in potting soil runs out over time. And in coarse bonsai substrate there are no nutrients available. For healthy trees, the plants need these nutrients. So.. Fertilizing is absolutely needed over the growing season.