The only time wildflowers need supplemental water is during prolonged droughts when the plants start to show stress. The size of the meadow is up to you. You can do an entire acre if you have the space, or just a small corner of the yard. Wildflowers make great borders along fences. They are also good for filling in areas that are difficult to mow such as a hillside or slope.
Most wildflowers do well in poor soil.
In fact, it is not recommended that wildflowers be fertilized. If a soil test indicates that the soil is depleted of nutrients, you can add a low nitrogen fertilizer. Fertilizing plants after they are established, though, tends to make the plants put on thick foliage, few flowers, and it encourages weed growth. In order to plant a wildflower meadow, the site must be prepared properly to avoid having problems with weeds and other grasses. Any existing grass and weeds must be removed.