I live on the Algarve, in Portugal. Mediterranean climate, summers 30C to 38C. No rain April to end October.
I had a lot of hibiscus plants in pots, which flowered beautifully. I moved house last year, and planted them out. Very hard red clay soil. Neutral pH. You need a pickaxe to plant anything, however I made large holes and filled them with good earth. I irrigate most days, and feed with 10-10-10 fertiliser, but they will not flower, about 1 flower per plant per month, although they are growing slowly but quite well. They are between 3ft. and 5ft. tall.
I would love some help with this problem,
Certified GKH Gardening Expert
It sounds like it they may be getting too much feeding. I would recommend feeding only once per month. It may be that there is salt build up occurring in the soil. I would also add dolomitic lime, as this will control the pH since the soil is likely fluctuating with feedings. Make sure to keep it watered very well with the clay soil around, as this tends to soak up water like a sponge once it finally makes it into the ground.
Here is an article for more tips on caring for hibiscus: https://www.gardeningknowhow.com/ornamental/flowers/hibiscus/how-to-care-for-hibiscus-plants.htm