Maybe a nice blend would be:

pelletized sulphur (fast acting to correct chlorosis or lack of acidity in the soil)
aluminum sulphate (does the same as pelletized sulphur but has an immediate effect...breaks down much quicker)
Scotts micromax macronutrients

and then follow a fertilization schedule on an acid-based product until no later than August 1st. Personally I wouldn't spend my own money on water-soluble fertilizers but would instead use a granular (slow release is best) but I don't have a suggestion for a brand name.

Good luck,

Dax

Hollytone is a good product with sulfur and trace elements. I recommend using it at half the rate on the package and using it once per year at the most unless you have nutrient related problems.

Now is a good time since it is a slow release product and most of the ingredients take time to become active.

In normal well drained acidic garden soil, rhododendrons and azaleas can thrive with very little fertilizer. Many estates use none at all.

I do not recommend the water soluble Miracid products. They are mostly nitrogen and very short acting. They are good in some greenhouse situations where growth is being forced, but can be a disaster in the garden.

No sulfur is fast acting since it is not water soluble. Aluminum sulfate will eventually kill rhododendrons and azaleas. The aluminum builds up in the soil to toxic levels. It is good for hydrangeas but not rhodies. For fast acting chlorosis treatment use a chelated iron product.

When rhododendrons and azaleas are not planted in ideal locations they may develop chlorosis. Chlorosis is yellowing of a leaf between dark green veins. It is caused by malnutrition that can be caused by a wide variety of conditions. They include alkalinity of the soil, potassium deficiency, calcium deficiency, iron deficiency, magnesium deficiency, nitrogen toxicity (usually caused by nitrate fertilizers) or other conditions that damage the roots such as root rot, severe cutting of the roots, root weevils or root death caused by extreme amounts of fertilizer. In any case, a combination of acidification with sulfur and iron supplements such as chelated iron or iron sulfate will usually treat this problem. Holly-tone contains these elements and 4-6-4 fertilizer. It is best applied in the spring prior to blooming to make sure the plant is healthy when forming next year's flower buds. If you missed applying it in the early spring, it can be applied up until mid summer. Rhododendrons do best when left alone in the right conditions. You don't need to use Holly-tone or any fertilizer unless the plant shows signs of malnutrition.

The National Arboretum warns: "Excess nutrients may promote larger than normal populations of pests like lace bugs and whiteflies.

Here is a link that might be useful: How to grow rhododendrons and azaleas.

Thanks much. While I don't typically have problems (chlorosis, lace bug, etc) growing any rhodie (eleps, leps, decidious natives, etc), at this time of the year I sometimes desire to use Hollytone (mainly on younger plants installed over the last 2 years or transplants).

Again, thanks for your objective input. You're a Godsend for us who love these plants.