Diana, Not knowing how long your plants have had time to establish themselves I will say this. Most plants of the type you are planting need at least a season to become acclimated to their new environment to flourish. Root development is a big part of the adjustment and phosphate (P) is one of the principle elements for root development. Root development will come with a well balance feeding program. And another important item to consider is that your "Drought Tolerant" plants will not be drought tolerant until they become well established. I would use a very mild dose of a low phosphate (P) continuous liquid feed program adding a 12% Humic Acid and Seaweed Extract included in the regimen. In addition, I will make this a very strong point. The addition of a Mycorrizae Inoculant Product is essential to your garden for the best establishment. This product will enhance the intake of moisture and nutrients more efficiently. The following is a brief explanation of Mycorrizae: "Most plant species form a symbiosis (mutually advantageous living arrangement) with beneficial fungi. The roots are colonized by the fungus, which also ramifies through the soil. The combination of root and fungus is called mycorrhiza (Mycor = fungus Rhiza = root). Mycorrhiza is considered such a fundamental part of the plant that most species could not survive in nature without it." My personal experiences with all the above has been highly successful. I believe that many of the drought tolerant apocynaceae plants such as Adenium, Pachypodium and Plumeria can be an important addition to the drought tolerant garden. They bring important structure, character and flowers to a sometimes boring garden. Jack http://cropsoil.psu.edu/sylvia/mycorrhiza.htm

Some grevilleas are really picky when it comes to soil quality. Most of them hate alkaline soil. They also dislike too rich soil, and too much phosphorus may even kill them. Overwatering may also present a problem since they are mostly dry climate plants. The following link gives you some good advice. Good luck with these beauties! I have a few myself. Here is a link that might be useful: Growing Grevillea

I doubt very much that pH is the cause of your problem. If as you say, the plant is showing normal growth then pH would seem to be fine. If you have a pH (iron deficiency) problem then the typical evidence would be stunted growth and pale yellowing on the leaves especially the new growth. How old is the plant? It could be that there is an excess of Nitrogen in the soil. If the plant is only a few years old then time will result in flowers. The plant will eventually exhaust the soil of those growth nutrients like Nitrogen, as long as you do not feed it for a while (until it flowers). Some Potassium can encourage flowering. Back off on the watering as well.

The problem with trying to grow Australian plants outside of Australia is that the soil there is deficient in phosphorus so the native plants have evolved ways to operate without it. When they encounter it they do not respond well. There are those that believe that one of the reasons that many Australian plants are relatively short-lived in our U.S. gardens is that eventually they overdose on the phosphorus in our soil. This is true of not just all Grevillea, but of all Australian plants. I have Loropetalum interplanted with Leucadendron, also Australian, but I have never, ever fertilized the Loropetalum (or anything, for that matter, except roses and citrus). Unless you have really poor soil you shouldn't need to fertilize most shrubs or trees. There are no tricks; just an understanding of each plant's native habitat and how you can best emulate it.