The authors find that slow plant growth at low temperatures during winter reduces dilution of the transcription factor NTL8, which allows slow accumulation of NTL8 and thus the gradual increase in transcription ofVIN3-a gene involved in memory of cold exposure. Temperature is a key factor in the growth and development of all organisms(1,2). Plants have to interpret temperature fluctuations, over hourly to monthly timescales, to align their growth and development with the seasons. Much is known about how plants respond to acute thermal stresses(3,4), but the mechanisms that integrate long-term temperature exposure remain unknown. The slow, winter-long upregulation of VERNALIZATION INSENSITIVE 3 (VIN3)(5-7), a PHD protein that functions with Polycomb repressive complex 2 to epigenetically silenceFLOWERING LOCUS C(FLC) during vernalization, is central to plants interpreting winter progression(5,6,8-11). Here, by a forward genetic screen, we identify two dominant mutations of the transcription factor NTL8 that constitutively activateVIN3expression and alter the slowVIN3cold induction profile. In the wild type, the NTL8 protein accumulates slowly in the cold, and directly upregulatesVIN3transcription. Through combining computational simulation and experimental validation, we show that a major contributor to this slow accumulation is reduced NTL8 dilution due to slow growth at low temperatures. Temperature-dependent growth is thus exploited through protein dilution to provide the long-term thermosensory information forVIN3upregulation. Indirect mechanisms involving temperature-dependent growth, in addition to direct thermosensing, may be widely relevant in long-term biological sensing of naturally fluctuating temperatures.