Hebes are natives of New Zealand, specifically the mountains of the south island. I think it is very unlikely that you will be able to grow them successfully in the heat of a Spanish summer. Along with shade you would need to water a lot, but even then I am not sure you will succeed.

I know that they don't work well here in the Arizona desert. Flynn, if your days are less than 40º C, and your nights are less than 21º C, then you have a chance. I would find a spot with morning sun, until noon, and shade the rest of the day. Condition the soil 1/2 meter down, and 1 1/2 meters wide with these proportions: 1 part gritty sand, 1 part rich compost, 3 parts native soil (what was dug out of the hole), plus 1/4 liter of soil sulfur. Mix all those up outside the hole, so there are no lumps or layers, put a couple of centimeters of the mix in the bottom of the hole, and scratch them in to make a transition layer, so the drainage isn't blocked. Then plant the young Hebe, taking care to leave 1/2 cm of the top of the rootball showing. Cover the soil with 5 cm of compost to help cool the roots, and keep them evenly moist. It still might not work, but that will give you your best chance.

Moon growe and Tugbrethil, thank you very much for your response, I'll try that, maybe it will work, I'll let you know if it does.