What is an ecological site? Do you mean a home garden, a public area, a protected area, a site restoration etc? More info and more specifics on what you need will help with some suggestions Helena.

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The secret is the soil.

OK. Still require more info. However, if it's a public place and you want it ecologically sound, you should look into what plants grow/grew there naturally, and what plants are indiginous to the area. Anything else is not strictly native. If you re-introduce local natives, you will immediately create habitat for animals and bird populations which have already adapted to using these plants. Also, look at creating a water or bog area if possible to supply water to these critters. The other advantage of using local natives is that you don't need to do much to the soil as they have adapted to the point where the soil is perfect for their requirements. The average rainfall will be just right and you know these plants will thrive if given a good start.

If you google 'wolverhampton native plants' and similar topics you may find a local nursery or regeneration society etc which can assist you and stocks what you need.
I take it Wolverhampton is in the UK?

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The secret is the soil.