Although daisies are somewhat indestructible, they can wilt in the hot weather. If they are dying, inspect the dirt in which the daisies are growing. SFGate suggests digging a 3-inch hole next to where the daisy is and check the soil to see how thin and dry it is. If the soil is too dry and thin, the daisies will require daily watering, especially in hot weather.
If the daisies are growing in thin soil, they need at least 1 inch of water every day until the organic matter in the soil can be built up. Avoid overwatering the plants, or else they may get fungal diseases. Soaker hoses help to avoid overwatering and make it easier to water daisies daily.
Once the daisy clump is dug up beside where the daisies are growing, apply a 3-inch layer of organic compost to the soil. Keep it several inches away from the plant stems. This builds up the garden soil and retains moisture.
Remove all weeds away from the daisies because the flowers do not like weeds growing near them. Most forms of daisies have shallow roots that cannot compete for moisture with the roots of more formidable species of weeds.