I have a garden in Mediterranean Europe (Zone 9-10) which is quite similar to the SW US and some US perennials have done a great job so far. I'm looking for the herbaceous perennials (not shrubs) that would thrive in the temperatures above 100 degrees F and would not need additional watering for the most of the year as I do not permanently reside there. Winters are wet anyway. The problem is that most of them (even those of african origin) are stressed by the heat and bloom before they should. They should be clay tolerant as well.

The prolonged drought this year started one month before and when I came there I was surprised to see threadleaf coreopsis withering. There was no track of blue flax I had planted. Even 4-o'clocks withered. Sedum pachyclados and cauticola were dying. I mean - succulents! All the other that were planted - bloomed way before they should normally bloom - apparently, they were stressed. Leonotis shrub bloomed in June, Agapanthus in June, everything bloomed just too early.

These are some that really did great job resisting the drought which lasts here usually for 5 months or more:

- Coreopsis verticillata

- Oenothera macrocarpa

- Oenothera speciosa

- Ratibida columnifera

- Campanula garganica

- Veronica spicata

- Delosperma cooperi

- Echinacea

- Gaura lindheimeri

- Zauschneria californica

- Salvias

- Agapanthus

These resisted drought the most, among some sub-shrubs like Perovskia and Leonotis. What are the most drought tolerant perennials that are maintenance free? Your suggestions. You can include the bulbs as well. Thanks everyone.