This process must not be rushed because over a period of days the natural waxes coating the leaves of the plants need to undergo changes in form and thickness to reduce water loss. The stomatal pores of the leaves also need to adapt to the less supportive conditions of the outside weather.
Start the hardening process by first turning off the heat in the propagator or mist unit. After a while, during the daytime raise the covers for increasingly long periods. Finally, remove the covers for both day and night. If the plants were grown until now in protective environment, like a greenhouse, and they need to be planted outdoors, move them into a cold frame for a period. At first this should also be closed then opened in stages.
If you do not have a cold frame than move the plants in the shelter of a wall, fence or hedge and cover them with horticultural fleece. Gradually lift the cover during the day and then during the night also. The total period of hardening off the plants may take from two to three weeks depending on how plants react and also how the weather is during this period.