Here is a very quick overview of the lessons I have learned.
Number one is: WATER, WATER, WATER. If you do nothing else to your flower beds, which hopefully are filled with daylilies, provide at least 1 to 1-1/2 inches of water per week. This is more important than any feeding program.
Number two on the list of "things to do" is to take pH readings in each of the locations where you grow daylilies. Regardless of how much nutrition is present, not much is going to be available to your plants unless your pH is in the 6.2 to 6.8 range. I've found inexpensive pH meters to be rather accurate when I compare them to lab tests of the same beds I've just tested with my "el cheapo" meter. In addition to the accurate pH test the laboratory will provide for you, it's important to get a baseline of what nutrition and element levels are present in your beds. You can't know what to add unless you know what you need. In the United States, your local County Cooperative Services may be able to provide this service to you at a very reasonable cost. Amend as necessary to correct any pH problems.
Whenever possible, incorporate as much organic material as you can get your hands on into your garden beds. Compost, composted leaves, animal manures, cottonseed meal, corn meal, bone meal, and the like will help keep your soil loose, provide valuable trace minerals, and retain moisture. This topic could be an entire article, but I'll stop here.
THE BIG THREE: The nitrogen, phosphorus, and potash (potassium) that we see listed on the front of our fertilizer bags deserves quite a bit of discussion. We must understand that our daylilies are not typical perennials. With most of our flowering plants a "balanced" diet is recommended lest we get too much leaf and little bloom. Thus 10-10-10 or 6-6-6 fertilizing programs are recommended. This is not the case with daylilies. Daylilies are monocots. Daylilies prefer to feed at a ratio of 3-1-2, or when in active growth 4-1-2. Thus, 18-6-12 should be an ideal mix for daylily growers. Compounding the typical lack of nitrogen problem, my laboratory tests always seem to reveal the fact that the middle number in fertilizer (phosphorus) is not easily soluble, while most of the nitrogen is quickly leached away. The bottom line is that if we do feed our plants year after year in the same beds, we may end up with much too much phosphorus, to the point where it is toxic. Before this happens, and if your soil tests come back showing that you have adequate levels of phosphorus, try feeding with small amounts of calcium nitrate (which will also help raise a low pH) or ammonium sulfate (which will help lower pH) and potassium nitrate throughout the season. This will provide the nitrogen our plants like along with other valuable elements. If you make a mistake, let it be putting out too little - not too much - of these products. They can be very powerful and can cause severe burning.
Early in the growing season, in addition to the basic fertilizer regime, it's important to add what I'll call the "major minors": iron (a minor element), magnesium, and calcium (both secondary major elements). Iron can come from a source such as Milorganite or an iron supplement. I get much of my magnesium from Epsom salts (which is magnesium sulfate) and apply at a rate of 100 pounds per acre, and additional calcium from the earlier-mentioned calcium nitrate. Several professional horticulturalists have told me it's important to get these "major minors" out early in the growing season, when needed, as they are required in order for the plants to be able to take up the Big Three (nitrogen, phosphorus, and potash). When I lived on Long Island, this active growth period started just after the dormant daylilies broke dormancy. The second very serious feeding period was after bloom season with the first cool weather in the early fall. It's important not to use a time-release fertilizer at this time, as we want our rapid growth to end before the onset of very cold weather. This second feeding period can result in twice the plant growth the following year as compared to unfed plants. In Florida or the Deep South, we can't feed too much in the summer due to the excessive heat, so most of the feeding takes place from November through March.
I've found that the frequent feeding of liquid plant food in modest amounts works wonders. It's also important to vary the product applied. A Peter's Excel product known as Cal Mag 15-5-15 seems to make my plants very happy. (A lab test will also tell you if the appropriate amounts and balance of calcium and magnesium are present.) I liquid feed any number of other products, most with a very high first number (nitrogen).
A last couple of thoughts. Firstly, risk using too little fertilizer - not too much. I can't say this in too loud a voice! Secondly, organic sources are better than chemical fertilizers; but for large gardens, we have little choice but to use the above-mentioned chemical fertilizers.