Fire maintains tallgrass prairies, but fire season is virtually unexplored as a formative influence of prairie floristics. Replicated mid—July burns, simulating the peak of lightning—caused fire in natural grasslands, strongly influenced species composition and cover in experimental restorations in southern Wisconsin. Perennials that flowered before mid—July showed only 17% cover in unburned plots and 6% in plots burned in March, but 46% cover in plots burned in mid—July. Late—flowering species dominating the remnants managed with dormant—season burns accounted for 80% cover in unburned plots and 92% cover in plots burned in March, but only 47% cover in plots burned in July. Management practices that employ dormant—season burns may produce quite different communities than those maintained by midsummer burns that simulate the timing of lightning fires.