Perennial wheat (Triticum aestivum L. × Thinopyrum spp.) and perennial rye (Secale cereale L. × S. montanum) are novel hybrid species under development as alternatives to annual cereal crops. We conducted a 2‐yr field study with a split plot design to evaluate agronomic performance, including yield, phenology, and biomass production, of perennial accessions of wheat and rye, along with annual analogs. This is one of the first studies to rigorously compare agronomic performance of 2‐yr‐old plants to 1‐yr‐old plants in perennial cereals. Perennial wheat produced 1.0 to 1.6 Mg ha−1 grain yield, 50% of annual wheat (2.7 Mg ha−1), while perennial rye produced 1.3 Mg ha−1, 73% of annual rye (1.8 Mg ha−1). Modest yields from perennials relative to annuals reflected lower harvest index, lower yield per tiller, and less kernel mass. One‐year‐old and 2‐yr‐old perennial plants had similar seed yields, yield components, and biomass production, indicating that plant age had little effect on these parameters and older plants maintained yield potential. In contrast, phenology did vary with plant age, and showed a shift toward earlier spring growth and later flowering dates in older perennial plants. This illustrates an expanded vegetative period for regrowing plants of these perennial cereals. There appears to be potential for producing an early season forage crop from these cereals, although biomass yields were not high at this site and regrowth was not always reliable. Overall, performance of perennial rye was consistent with a viable new cereal crop. On the other hand, perennial wheat requires further selection for allocation of biomass to grain and vigorous regrowth.