Heres what Ive done:
50% native soil, 50% compost.
Mulch heavily in winter to preserve warmth in soil. Plant tomatos in front of vine to deflect some summer sun, then mulch with the tomato plants "leftovers" after the Phoenix sun scorches them in May or June. Soil is cooled and fertilized with this through summer, so I only have to add a minimal amount of fertilizer during our hot summers.
Feed with Peters 20-20-20 with epsom salt added all through the early spring. I switch to super bloom 10-55-10 about mid spring for bloom strength.
Ive no idea if this is the ideal, as I think age of the plant and good soil characteristics have the most influence, but my plants look healthy and produce large, showy blooms on this regimen.
DD

I'm glad to hear a little of what others are doing as this is a subject I've thought about myself. What I've heard usually amounts to "don't use too much nitrogen."
About how much epsom salts do you use?

One tablespoon of epsom salts per gallon of water. I just throw the epsom salts in with the fertilizer water.

As far as fertilizer goes, one size definitely doesn't fit all. In the heavy clay alkalai soils I have, extra phosphorous and potassium aren't needed. Adding that with fertilizer could even cause problems. I do a general broadcast of nitrogen late winter/early spring, another general broadcast of iron (the alkalai soil can cause iron chlorosis) and spot treat certain areas (grapes, fruit trees, roses) with sulphur to increase the acidity.

While pretty much every source on the matter says passiflora prefer neutral, light and well-drained soils, the ones I have in the ground are thriving. Well-drained is the key, I think. We're situated partway up a hill, and while the clay holds moisture a long time, there's never any standing water no matter how much rain we get. That's makes all the difference in the world.

Excellent point about drainage. I forgot to mention that all my passies are grown on a slope. Ive built mounds against my block fencing with native, alkalai, heavy clay, mixed liberally with good quality compost, mulched regularly. I also acidify my soils with sulphur and an occasionaly watering with pH'd water (I put it on at pH 6.0, which is accomplished through the use of an apportioner filled with dilute sulphuric acid. Our water out of the tap often measures 8.5!).
Further, the point about iron chlorosis applies to me as well. Added iron keeps my plants green and healthy. I apply it two or three times a year, because of our alkaline soils and salty water here in Phoenix. Really seems to help a lot. The heavy soils trap a lot of the nutrients, which is key for me, as fertilizing between June and Sept. is difficult in our heat. Nitrogen burn, and even phosphorous toxicity, can result, in my experience.
A final note: I use fish emulsion for the first few fertilizings when I get a new plant (and even beyond that. If a plant is sensitive to nitrogen burn, Ill use fish emulsion exclusively for the first year or so, until it has reached adequate size to handle some higher nitrogen feeding). This prevents burn, and the general make up of fish emulsion insures adequate nutrition including minors. I like the stuff, and its about all Ill use in my greenhouse. Things seem very green in there, so it is doing what I need it to do....
This is a good topic, as we all seem to have gotten the same vague advice at some point. Also, keep in mind that we dont all fertilize for the same effect. I use more nitrogen than most because of: 1. an almost total lack of organic matter in our native soils, and 2. I am shooting for larger plants, as most of mine die back quite a bit in our winters. Therefore, I use a higher nitrogen feed at the beginning of spring to encourage rapid growth of the plant itself to cover the block walls (this also helps conserve some ground moisture by virtue of spread along the ground. Another consideration here with our intense sun and the resulting evaporation). Other growers are more interested in an intense bloom, and use less.

Hope this helps. I know I learn a lot from each passionflower grower I speak to! We each have developed a pattern that suits our climate and soils, so it is interesting to compare notes.

DD

Excellent post, desertdreamer. Big box stores, and most chain nurseries for that matter, don't adapt their offerings for the region. For years, Wal Marts here in Texas stocked Japanese beetle traps--and there *are* no Japanese beetles in Texas. They stocked them simply because *all* Wal Marts stocked them. Centralized distribution and all that. I'll go to a nursery or Lowes or Home Depot and see them stocked with gorgeous grape vines for planting--then realized all those lovely plants are either Concord grapes (which will die a painful death in our heat) or European varietals (which will die a quick death from Pierce's disease) and just shake my head. Every so often I'll stumble across a lone Champanel or Black Spanish or even (!) muscadines and marvel how something actually appropriate made it onto the selling floor. LOL

One of the best things a homeowner can do is contact their local county extension agent or equivalent. They usually will do soil analysis for a modest fee, and can then tell you exactly what you should be putting down on your yard, when and how much.