If you plan to move herbs outside in the spring after wintering indoors, you need to acclimate them before leaving them outside all day and night. Much like you harden off new plant starts before they go into a vegetable garden, you need to gradually reintroduce indoor herbs to outside conditions.
They have been pampered inside and are not used to wind, rain, and
direct, hot sun.
Move potted herbs outside for a few hours each day when temperatures average in the upper 60s (about 19°C). Gradually increase their time outside every day by an hour.
Cloudy days are best, but more important is that the temperature is warm and stable.
You don’t want to shock them too much with an abrupt temperature change.
If the sun
is direct or very hot, place the plants in a shady location for the first few days.
Bring plants back in overnight.
Follow this routine for about a week. As they get used to accessing more light and having the wind on their leaves, they will start actively pushing new growth. They should be okay to leave out after that.
Some tender plants, such as lemon verbena and basil, may take a few weeks.
After they are acclimated, cut back any soft growth on perennial herbs to encourage new growth to be lush and leafy.