Perfect for gardens in temperate mood , hydrangea ask a winter dormancy that is punctuated with frost and subfreezing temperatures . However , if a hydrangea bush is leafy or in efflorescence , rime will scald it and twist the plant tissue brown , and the flower petal and leave will cut down off . wrong spring frosts can kill efflorescence and leaf buds on shrubs , and reduce or forbid flowering afterwards in saltation and summer .
Species
agree to the American Horticultural Society ’s Word , " A - ezed Encyclopedia of Garden Plants " , about seven species of hydrangea are wide crop . Common hydrangea include the placid hydrangea ( Hydrangea arborescens ) , Sargent ’s hydrangea ( Hydrangea aspera ) , bigleaf hydrangea ( Hydrangea macrophylla ) , peegee hydrangea ( Hydrangea paniculata ) , oakleaf hydrangea ( Hydrangea quercifolia ) , mountain hydrangea ( Hydrangea serrata ) , climbing hydrangea ( Hydrangea petiolaris ) and Villosa hydrangea ( Hydrangea villosa ) .
Cold Hardiness
These non - tropic shrub turn in area with cool to moth-eaten winter , in USDA Hardiness Zones 3 through 9 . Each species or hybrid hydrangea has unique , varied hardiness within these geographical zone . These zones are susceptible to Robert Lee Frost in fall and winter , where mean minimum temperature drop below 30 point Fahrenheit .
Effects of Frost
In spring , when flower bud tumesce , a late time of year rime causes buds to drop off , diminishing the succeeding flower presentation . Protect shrubs from a late frost by covering them with a cloth bed sheet or blanket when unseasonal frigidness is forecast . plant snip off by frost should be cleaned and clip only when there is no further threat of frost in spring .
Frost causes hydrangeas ' flower petal and leaves to become browned in early to mid - autumn . Although the petal may be lost , some foliage may remain and over the path of the next 3 to 14 days may change from dark-green to rust fungus , orangish , or burgundy before fully falling off the shrub . Old , dry out flowers that stay on the shrubs will not be affected by the cold .
hydrangea impel in containers for seasonal florist shop sales are susceptible to folio and flower damage if exposed to immobilise temperature . These potted plants are grown in greenhouses and if abruptly expose to cold-blooded zephyr will be harmed during transport or if unintentionally left outdoors on the patio on a nipping night . The plants wo n’t be killed , but the foliage and flowers will turn brown .
Frost Requirement
hydrangea are shrubs aboriginal to eastern North America and eastern Asia where nerveless to cold winters occur . The hydrangea needs the autumnal frost to start its yearly dormancy . The protract temperatures below 40 degree Fahrenheit in wintertime allow the heyday bud to open up fully the following spring . Newer modern hydrangea hybrids , such as the bigleaf hydrangea , do not want wintertime stale prime .
Benefits of Frost
Frosts and cold winter temperatures kill insects and eggs . Leaves infected by jet-black mold are killed and set down from the shrub . The cold help to vote out drying , sickly and sure-enough stem .
