Harvest stevia in the late fall, before the first frost or as soon as the blossoming begins, when the sweetener is at its strongest.
Cut the branches with pruning shears. Leave 1/3 of the plant's foliage so it may continue growing the following season.
Strip the leaves from the branches.
Dry the leaves on a screen or net. Leave them outside in full sunshine for 8 to 10 hours. Alternately, use an electric dehydrator on low (100 degrees F to 110 degrees F).
Stop drying when the leaves are crisp, crumbly and bright green. Avoid overdrying (the leaves will lose their sweetness).
Crush the dry leaves by hand or with a coffee grinder or herb blender.
Keep and use the herbs in their crushed form or make liquid stevia extract.
Add 1 cup of water to 1/4 cup crushed leaves. Let it set for 24 hours; pour the extract into a jar. Keep it refrigerated.