Wow ...you have leaves.
I am 50 days behind you.
First, you plants love this cool spring weather weather and a lot is happening underground and out of sight many weeks before your plants leaf out.
Fertilize with the spring rains or water well the summer months.
A farm/agricultural oriented store will have all the fertilizer choices for you....much more than a big box store.
46-0-0 (urea)is an optional VERY early spring high nitrogen boost and is used with care before your plants leaf out. While not really necessary it does give your plant its first nitrogen feeding.
Only to be applied early(cool) and with spring rains to work into the soil.
Brand names vary by region and is sold in 50 lb bags.
The fertilizers for these plants are a well balanced general use granular fertilizer good for all plantings.
You may use triple 12-19 with slight noticible difference .
You/me would not know the difference which fertilizer was used as the season progresses.
I buy end of season(deep discount) and what is on sale and what I can afford....... in a pinch I have used lawn fertilizer with no issues.
Purchase a few years worth if the deal is good.......just keep it dry.
I use the same fertilizers for all the landscape plantings in the yard.
Exceptions are the container plants which get a water soluble type mixture.....nothing special.
Your basjoos will only get so large and size is determined by age and a lot is always happening underground with runners and pups.
Once a few seasons go by you will notice predictable results and growth with your new way to do things you will say "I got this"
Right now daffodils are coming up so that is my que to get out and check things out.