Hardening off

Hardening off / getting used to circumstances outside

Sun
Plants often can, just like people, bear all sorts of weather conditions, provided they get used to these gradually. A plant that got used to relatively "dark" circumstances indoors can, when put outside, be badly burnt by sun. Therefore they have to get used to it during at least a fortnight, (for instance, under a garden-table) and protected from wind, before they can bear direct sunlight even for a few minutes.

Cold
A Hydrangea can be moved directly from inside to outside, provided it is not freezing.

Wind
Do not put a plant from inside into strong wind, but into a sheltered position, so the plant has time to get used to it.

Frost
Night-frost/late frost in spring. If in spring the young buds are sprouted, protection against night-frost will be necessary.

Frost in winter. The first winter after being planted outside, when the plant has not made roots sufficiently and there is continuous, bleak, drying frosty weather (surely with icy sharp wind), no moisture can be transported from the roots to the stems and buds, especially if the soil is totally frozen. Hydrangeas will not be frostbitten easily but will rather dry because no moisture can be transported to the aboveground parts of the plant. Drying out has to be avoided by covering the plant with plastic, by preference with bubble-plastic, during extreme conditions. The Hydrangea has to be planted as early as possible in spring when there is no chance for late night-frost anymore so the plant will have the opportunity to make deep roots before winter. See also "Winterhardiness and vulnerablity to frost".

Manuring
If the plant will be manured in late summer or in autumn it will still be growing when frost comes. The still-growing and therefore weaker parts of plants can be frostbitten then easily and this means less flowers next season. If manuring has been stopped about late July/early August, the plant will have the opportunity to harden off and will be strong enough to go into winter.

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