Catmint (Nepeta spp.) is easy to grow in full sun or partial shade, is not particular about soil type or pH, and does best without any fertilizer. It has a stronger fragrance and blooms better when grown in nutrient-poor soil. It is generally hardy in U.S. Department of Agriculture plant hardiness zones 3 to 8, although this varies slightly depending on the species or cultivar.
Catmint is not commonly propagated with seeds because many of the hybrids are sterile. Propagating it through clump division or cuttings is more reliable and produces plants exactly like the parent plant.
Divide catmint clumps in late September or early October after they are three to five years old.
Prepare for Division
Trim the stems down to a height of 6 inches with sterilized pruners.
Use a shovel or garden fork to loosen the clump by pushing it into the dirt about 6 inches from the stems all the way around the plant. Push the shovel in again and lift the clump with the tip of the shovel or fork tines.
Cut Into Sections
Catmint has a clumping root system, which means the roots all grow from a fleshy base, or crown. Use a sharp, sterilized knife to slice through the fleshy crown and cut it into smaller sections. Each section must have healthy roots and at least one developing growth bud, or eye. Growth buds are small, raised bumps on the crown.
Replant Smaller Clumps
Replant the new catmint clumps right away at the same depth they were growing originally. Water them generously after planting. Continue to water them when the top of the soil begins to dry for a month after planting.
Rooting Catmint Cuttings
Take 4- to 6-inch-long softwood cuttings in early summer. Water the catmint the day before taking the cuttings and take them in the morning so that they are well hydrated.
Make the Cut
Use sharp, sterilized scissors or pruners to take the cuttings. Make the cut just below a set of leaves. Each cutting must have a minimum of three sets of leaves. Trim off any flower buds. Remove the leaves from the lower 2 to 3 inches of cutting. Trim back the remaining leaves by half.
Prepare a Rooting Container
Get the rooting container ready before taking the cuttings so that they can be planted right away. Use coarse sand, perlite or vermiculite as the rooting medium.
Pour the rooting medium into a 4- to 6-inch-deep pot or flat with holes in the bottom. Moisten the medium thoroughly. Poke 2-inch-deep planting holes spaced 4 inches apart in the rooting medium with a pencil.
Pour a small amount of rooting hormone into a container. Dip the bottom 1 inch of each cutting in the rooting hormone.
Plant the cuttings in the 2-inch-deep holes and firm the rooting medium around them. Insert 6-inch straws or sticks in the medium along the edges of the container.
Put the planted pot or flat in a clear, plastic bag and seal it shut to hold in moisture. An empty milk jug or 2-liter pop bottle with the bottom cut out can also be used to keep the cuttings moist. Leave the cap on and set it over the cuttings.
Provide Light and Moisture
Place the rooting container in a bright area but not in direct sunlight. Maintain temperatures between 70 and 75 degrees Fahrenheit.
Mist the cuttings each day. Moisten the rooting medium if it begins to dry.
Look for Roots
Check the cuttings for roots one week after planting. Grasp each cutting gently between thumb and forefinger and give it a light tug. There will be resistance if there are roots. Replant the cutting if roots have not formed and check it again in a week. Catmint cuttings should root within one to two weeks.
After they form roots, leave the plastic bag open or remove the cap from the milk jug or pop bottle. Remove the cover completely after another week.
Pot New Plants
Pot the rooted cuttings in small pots with holes in the bottoms using houseplant potting soil. Water them generously. Set them in front of a window where they will get morning sunlight. Water them as often as necessary to keep the potting soil moist.
Harden New Plants
Begin to harden the new catmint plants a few weeks after potting them. Set them outdoors in a shady, protected area for a few hours the first day. Gradually increase the amount of time they are left outside. Move them into morning sunlight after about a week and gradually into full sun after another week or two. During this period, let the top 1 to 2 inches of potting soil dry before watering.
Move to the Garden
Plant the cuttings in the garden after they have adjusted to being outdoors. Plant them at the same depth they were growing in their containers. Water the plants as often as necessary for the first few months until they get established.
Getting the Best Growth
Space catmint plants far enough apart that they have room to grow to their mature width. Catmint plants grow between 1 and 4 feet wide, depending on the species or cultivar. Spread 2 to 3 inches of organic mulch over the soil around the new catmint plants.