1. There is substantial evidence that the rate of litter decomposition is affected by the match between the litter substrate and the soil matrix (decomposer community). We introduce and test the phenology-substrate-match hypothesis, which predicts that both litter composition and soil matrix will change over the course of the year, and that a lagged match between litter type and soil matrix will result in an optimal decomposition environment. 2. We conducted a decomposition experiment in a Mediterranean mixed deciduous-evergreen oak savanna in California. We initiated litter decomposition of both a deciduous oak (whose leaves fall in autumn) and an evergreen oak (whose leaves fall in spring) in both autumn and spring. 3. Consistent with the phenology-substrate-match hypothesis, we found that decomposition of deciduous oak litter was accelerated compared to evergreen oak litter when decomposition was initiated in spring, while evergreen litter was accelerated compared to deciduous litter when decomposition was initiated in autumn. 4. We also found a small effect of microsite on leaf decomposition, where both evergreen and deciduous oak leaves decomposed faster under the canopy of a conspecific. 5. Synthesis: Our study extends theory of litter quality and the decomposer community into a temporal context which may be an important source of variation in decomposition rates when species with different litterfall phenologies co-occur.