Ask Mr. Smarty Plants

Why don't you begin by reading our How-To article on Meadow Gardening. You will note in that article that experts consider that a wildflower garden should have 50 to 80% in grasses. Obviously, you don't want non-native or invasive grasses or weeds in that garden, but neither can you expect to have nothing but wildflowers. The grasses will protect and support the wildflowers, and fill the space when the mostly annual wildflowers are dormant. Permitting the wildflowers to self-seed, as well as re-seeding, should continue the show into future years. In the long run, the grasses will probably dominate. Using an herbicide will only kill the plants that are above ground at the time of application, but many grasses have extensive underground root systems, and some have rhizomes that are little affected by herbicides. We do not recommend continued use of herbicides, as it will inevitably destroy some desirable plants and, over time, affect the quality of the soil. Since most annual wildflowers reseed themselves in the Fall, you can possibly mow, at a high setting, some of the grasses in the area, and certainly pull out any aggressive weeds. Mowing the grass before it sets seed is the most effective way to prevent it continuing to spread. However, there will always be seeds in the wind or carried in by birds, no matter how carefully you protect your area. Pulling out weeds, particularly before they flower and set seed, is hard but about the most effective way to control them.

We would also like to suggest that you read this article on Wildlife Gardening. You may find that you can offer a haven for other wildlife than just birds, enriching your experience with your garden.  The more diversity of plant life you have, the richer the experience for you, your birds, butterflies, and other small creatures.