- Spring is a very critical period. Plants on open ground may warm under solar radiation (temperatures above 20 °C are possible anytime). If plants took such daytime warming as the arrival of the growing season and gave up their dormant (hardy) state, the next cold spell would kill them.
- Therefore such plants control their dormancy by a temperature independent "internal calendar" driven by photoperiod (the relative length of night vs. day). Such plants use "photoperiodism" as a safeguard against becoming active at the wrong time.
- In contrast, snowbed plants are opportunists, they become active whenever the release from snow and temperatures permit.
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1 - Photoperiodism prevents the breaking of plant dormancy at the wrong time.
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