- Then if your plantations are in jar, return in greenhouse, porch or in inside; the plantations of stevia support the cold but not on the long term especially in jar (the jar does not protect as well the roots as in full ground).

- If your plantations are in full ground, you can earth up the foot, that is create a small hillock defender around the remaining stalk because roots, which are close to the surface, are afraid of the cold. You can also use a natural ground protection as it is common to make with the fragile plants. Once frosts are over, remove your protections and your plantations will restart from the foot.

Note that if you are not resolved to cut your plantations, the fact of bringing in them risk to make them lose their leaves ; it is normal, you modify their conditions of life and the shock is rough.
This loss of leaves is not grave, your plantation did not die for all that. If it has enough roots and if you do not spray it too much during winter, (so that roots do not rot) the regrowth will make carefree in spring after repotting and contribution of essential nutriments in the good development of the plant.
Finally, you can then follow the advice number 1, by cutting your plantations between 5-10cm of the ground.