It sometimes takes a while for them to get going in the spring. My reds are blooming, but the pinks don't even have a bud and they're all the same size.
I use a regular balanced fertilizer with success. Perhaps others ahve more specific adivse.
Barb

I live in Zone 8 Summerville Sc and have several varities of Hibiscus. I am a novice to many and have several tropicals. One of my tropicals returns like a perinnial every year going on three years. I have green leaf growth of up to 4 inches. it usually comes to full maturity by the middle of June. I have others I have rqaised from seed and they are in full bloom. I use 10-10-10 standard fertilizer and Preen time release fertilizer on my potted hibiscus. My soil content is varied. I use sand and rich top soil mix with 10-10-10 mix to Mirical grow potting mix to regular SC soil with with 10-10-10. The reds love the first mentioned mix and I they are full of buds. I counted 50 on one group.
I have 50 hibiscus I have raised from seed and I started late. They are about 3 inches tall. Do you know how tender they are at that stage. Can you trnsplant them into pots that young? I have never tried it.

I have two tropical hibiscus trees that I've had for about 5 years. I use Miracle Gro for tomatoes for fertilizer. They are between 4 and 5 ft. tall and almost as wide. I bring them in every fall--the leaves always turn yellow and then fall off and they look dead. In the spring, they start to leaf out and bloom in the summer more beautifully than the previous year. They have a lot of buds right now.