When your favorite herb plants are well established, you can increase their number, or grow a couple of insurance plants in case some don’t survive a harsh winter, by using various propagation methods.
Choose softwood cuttings from young stems in spring, semi-ripe cuttings from ripening, stiffening stems in late summer, and hardwood ones from woody stems at the end of the growing season.
Take a healthy, non-flowering stem with mature leaves, cut the stem at an angle just above the leaf attachment, and strip the lower leaves.
Cut the stem straight across 2in (5cm) below the last leaf. Plant vertically in a pot of soil. Water well. Cover with a clear plastic bag to conserve moisture.
Make new plants from sections of semi-mature or mature roots of plants such as mint when they’re dormant in mid- to late winter.
Lift the plant and tease the roots apart. Cut a 2in (5cm) piece of root; avoid fibrous or immature roots.
Trim the root straight across at the top and diagonally at the base. Plant upright in soil. Cover with vermiculite.