As the temperature gets to freezing or below the sap in the stem of the plants will expand. As it does so the outer layer of the stem comes under increasing pressure and microscopically thin cracks, known as linear fissures, begin to form. These will finally give way under the pressure of the sap and split open
Inverno em São Joaquim, estado de Santa Catarina, Brasil. Na serra catarinense, em algumas regiões no Paraná e Rio Grande do Sul, havendo condições meteorológicas adequadas, a geada é certa, e ocasionalmente pode nevar.
Image Credit Flickr User Cotinis Not only that, as they are made of such thin sheets of ice, they will melt away as the sun rises higher in the sky. You may get frost flowers again the following day, but unless the conditions are just right the chances are your first glimpse may be your last.