Growing Herbs from Stem Cuttings

As a human, I can easily comprehend plant reproduction from seed: like our own approach to procreation, it’s sexual ­reproduction. Many herbs also reproduce asexually (vegetatively) by producing structures such as offsets and bulbils that eventually become independent. But one kind of vegetative propagation is utterly foreign to my human condition: a complete plant can be regenerated from a severed piece of stem or root, a bud, a leaf or leaf part, even a small group of certain plant cells.

To me, this capability is awe-inspiring. Even more exciting is that a novice gardener like me with only a windowsill to work with can, with patience and understanding (and perhaps a little divine intervention), propagate many herbs from cut pieces of leafy stem. Many people have even rooted fresh-cut herb sprigs from the produce department at the supermarket.

How Herb Cuttings Root

When you cut off the end of a stem, you inflict a wound and cut off the water supply, and those two events determine what you and the cutting must do next if the cutting is to survive. Its job is to heal the wound and make new roots; yours is to provide a suitable ­environment-water, light, air, temperature, and soil-to keep it alive during that process.

Roots are most likely to develop at a stem wound that is in firm contact with moist soil. When a plant is wounded, hormones called auxins collect briefly around the wound and alter the ­nature of cell division in the cambium (inner “bark” of the stem) so that it begins to form embryonic root tissue. Meanwhile, callus material forms over the wounded area. If the wound is ­exposed to air, the callus dries and becomes hard; in contact with moist soil, the callus remains somewhat soft, and the burgeoning roots beneath it can emerge.

When to Take Stem Cuttings

Cuttings taken from herbs that are growing steadily (generally from spring through fall) have the best chance of rooting. The growth of many species slows down when temperatures drop and days get shorter, even if you bring them indoors, and cuttings taken then will root slowly if at all. However, you can take cuttings anytime from a plant that doesn’t slow down while wintering indoors. Cuttings with flowers forming on them are not likely to root strongly; if you decide to take cuttings when a plant is flowering, nip off the flowers to shift the cuttings’ energy into making roots.

Most herb stems darken as they harden, and the newer growth toward the tips will be a lighter color than that farther down. The succulent new growth is easiest and most likely to root; when the stems are just firm enough to snap instead of bending, they are ready to be taken as cuttings. Bay (Laurus nobilis) is a notable exception: take hardwood cuttings late in the season. Whatever the condition of the stem, it is wise to take cuttings only from the current year’s growth.

Plants that have been heavily fertilized to stimulate lush growth produce poor cuttings: it takes time for stems to store up the reserves needed for rooting. Choose plants, and stems of those plants, that are healthy and growing steadily. Cutting back the longer stems in late spring usually produces a large number of side shoots that will make excellent cuttings later. Meanwhile, you can root the tips you cut off-you may be overrun with new plants by season’s end.