The National Gardening Association lists the types of wildflowers that do well in drought conditions.
Q. Which wildflowers do well in drought conditions? We have a summer home in Greece surrounded by a lot of dry soil that we would like to sprinkle with wildflower seeds to cover. There's hardly any rain in the summer and it gets very hot. Also, the soil conditions are probably not the greatest.
--C.P., Silver Spring, MD
A. Sounds like what you need are native prairie wildflowers. Plants that grew in the Midwest prairies had to survive long droughts and tough conditions, although granted, the soil conditions were not too bad. Plants such as black-eyed Susan, butterfly weed, monarda, ironweed, purple coneflower and liatris should establish nicely. Many of the new varieties of goldenrods and asters should do well also.
Prairies are usually established with prairie grasses as well, and these mix well with prairie plants: little bluestem, prairie dropseed, swithchgrass, side-oats gramma. The real trick will be establishing the plantings the first year. If you were to plant seeds, you would need to water probably every other day for the first month, and weekly throughout the first summer. If you were to use transplants, you would still need to watch the soil conditions all summer until the plants are well established, watering each plant deeply on a weekly basis. The second year and beyond, the plants should do well with less attention. This type of wildflower area is not the cottage-garden look; it's much more "untamed," beautiful, but definitely natural.
--National Gardening Association