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Naturalists have long observed and reported sequential flowering among plants of the northern prairie grasslands. Stevens reports on first flowering along the Red River near Fargo, ND, and Moorhead, MN (Stevens 1921, 1973) and on the flowering of weeds and woody plants in North Dakota (Stevens 1956, 1972). Godfread (1976) gives general flowering periods for over 300 plants collected in Barnes and Stutsman counties, North Dakota. Phenological data for plants in northeastern (Willenbring 1971) and southeastern (Manske 1980, Seiler 1973) North Dakota and southwestern Montana (Mueggler 1972) are available. For Canadian prairies, phenological information is published for Treesbank, MB (Criddle 1927) and Swift Current, SK (Budd and Campbell 1959).

The only analysis of the effects of climatological variables on plants of the northern grasslands is that of Mueggler (1972). He found May precipitation positively correlated, but maximum temperatures of the shaded soil surface in June and July negatively correlated, with herbage production.

The major factors influencing timing of plant flowering are genetic makeup, photoperiod, and other environmental conditions, especially temperature, moisture, and nutrients (Garner 1933, Roberts 1939, McMillan 1957, Mueggler 1972, Noggle and Fritz 1976). The perennial plants dominating the mixed-grass prairie undergo a rest period during the winter, and their rest periods normally cannot be broken without exposure to low temperatures. Once this requirement is met, the plants resume activity in the spring as soon as their threshold temperatures are exceeded and provided no other adverse conditions such as insufficient day length or lack of moisture exist (Daubenmire 1959).

The purpose of this paper is to provide additional information on first flowering dates and flowering periods for upland plants on native and seeded grasslands in central North Dakota and to address the influences of temperature and precipitation on the time of flowering.