Fertilizing is much more complicated than watering because there are no two growers who agree on the best way to fertilize.  Liquid feed, organics, time release, green sand, alfalfa meal, and who knows what else.  I've seen hostas described as heavy feeders and I've seen test results that indicate that using a balanced fertilizer at half the recommended rate produced the best results.

My own personal opinion, based on 25 years of growing hostas, it doesn't matter.  Fertilizer is fertilizer. I do recommend fertilizing, but I don't think it makes much difference how you do it.  When people want to know what to use, the first question I ask is "What kind of fertilizer do you already have?"  Chances are, that's as good as anything.

I think the most important thing to remember is that we fertilize plants to provide the nutrients that are lacking in the soil.  The best way to do that is obviously to start with a soil test to find out what's already there. Over the years I have suggested a soil test to hundreds of people, and I suspect that at least three or four have actually had one done.  Since you're never going to get a soil test done, your best bet is probably a balanced fertilizer, maybe a liquid feed of Miracle Grow, Peters, or something similar in the early spring, followed by a slow-release, organic, or just a cheap dry garden fertilizer when the soil warms up.  If you want to do more than that or get fancy, go ahead.  It probably won't do any harm.

Here's a story that's really true, not just something I made up to illustrate a point.  Several years ago I decided I needed to get more serious about our growing methods here, so I talked to several growers about how they fertilized.  At one of the nurseries that had always grown great hostas, I thought their plants looked especially nice that year. I talked to the head grower and she told me that they had switched from slow release fertilizer to liquid feed that year and were very pleased with the improved growth of their plants.  She liked the control that the liquid gave her.  She could adjust the feeding to the weather and to the plants' needs.  The rest of the story is probably predictable so I won't drag it out.  Another grower went just the opposite direction.  He told me he had changed from liquid to slow release fertilizer and he couldn't believe how much better his plants were growing. The plants were fertilized constantly during the warm months when they needed it, with little or no feeding when it was cool.  He didn't have to worry about a feeding schedule because his plants always had the nutrients when they needed it.

All general purpose fertilizers do essentially the same thing.  The most important consideration in choosing the right one is your gardening practices. There is no single answer

Again, we should probably call on some common sense gardening here.   If you use liquid feed and you water like I told you to, the fertilizer is going to be washed through the soil and so you have to fertilize regularly.  If you are not inclined to think about fertilizing regularly, then longer lasting dry fertilizers are probably a better choice.  Read the directions on the fertilizer you're using.  And remember that the directions were written by people who's job it is to sell fertilizer, so you can probably cut the recommended amounts in half. 

Here's the rest of that last story, which, again, is really true.  I got some plants from the second grower, the one who had just switched to slow release fertilizer.  They had used a broom handle to make a hole nearly two inches deep in the pots and they filled the hole with fertilizer. The plants were beautiful, but  we noticed that all the growth was on one side of the pot.  When we took them out of the containers, we saw that all the roots had rotted on the side where the fertilizer was buried, and nothing was growing on that side.  Using too much fertilizer will do more harm than using none.  It's like pouring salt on your plants.

Start fertilizing in the spring, when the plants are first coming up and stop early to mid summer.  It's best not to fertilize late in the year because you don't want to encourage tender, young growth going into winter. In our area, we stop fertilizing in August.  Once again, that underused gardening tool, common sense is the best guide.  If you have great soil and the plants are growing well, you don't need to fertilize a lot.  If your soil is poor and your plants are not putting on the growth you think they should, you may want to increase feeding. 

A word of caution.  Some gardeners seem to think that fertilizer is a cure for whatever ails their plants.  If your plant starts looking a bit under the weather, dumping fertilizer on it may be the worst thing you can do.  Again, the common sense thing to do is find out what's wrong before you try to fix it.