I lived in Galdewater (zone 8) a year and the clay soil was so water-retentive, that the soil had to be seriously amended. It was expensive. The shrubs that did quite well with the addition of some perlite, light potting soil and mulch of pine bark were lantanas. Lovely little flowers, hot summer sun ok, but keep somewhat moist, and they come back every year. They like slightly acidic soil, so I fed them a tsp. of vinegar in a half gallon jug of water on occasion. They also like rose fertilizer, but seemed happy with the vinegar. They will grow up 3 ft. or more and pollinators visit.