"Too cold" for holding the wraps is under about sixty degrees. Less than that and they are produce being held in a vegetable crisper and like produce, they hold in the same form as you put them in. They won't callus, but they will continue using their stored nutrients until they collapse from malnutrition. The optimum temps for callusing appear to be from about sixty to just under seventy degrees. Much over seventy and they attempt to leaf out and your chances of mold and rot increase greatly. Remember, they are being held in tight contact with DAMP, no drippy, paper. Mold grows readily in warmer temps. More than about 69 degrees appears to be perfect for the paper and cuttings to mold, getting gray and fuzzy.
Also remember that bare root roses are held in damp storage at just above freezing temps. The colder they are held, the slower their cellular activity. Properly stored bare roots have been held for six and seven months and remained viable for planting. The warmer the temperatures they're held under, the shorter the length of time they can sustain themselves, and the greater the chances of them molding. Between sixty and about sixty-nine degrees, you can hold cuttings safely for two weeks. Holding them longer has substantially reduced their viability once planted. It appears they use up their stored nutrients before they can push roots and foliage to feed themselves.
