Catmint, belonging to the genus Nepeta, is a durable perennial herb prized for its long blooming season and aromatic foliage. Growing catmint from seed is an economical way to establish a large border or groundcover patch, allowing gardeners to cultivate a high volume of plants without the expense of purchasing nursery starts. The process requires a preparatory step that significantly impacts germination success.
Preparing Catmint Seeds for Planting
Many perennial seeds, including those from Nepeta species, require a period of cold, moist conditioning to break their natural dormancy. This process, known as cold stratification, mimics the damp, chilly conditions of a winter season, signaling to the embryo that it is time to germinate. Skipping this step often leads to erratic or poor germination rates.
To perform artificial stratification, mix the seeds with a moisture-retaining medium that is lightly dampened, such as peat moss, fine sand, or a wrung-out paper towel. Seal the seeds and medium inside a labeled plastic bag or container. Place the container in a refrigerator, maintaining a temperature near 4°C (40°F).
This cooling period typically needs to last for approximately three to four weeks before the seeds are ready for planting. Alternatively, gardeners can achieve natural stratification by sowing seeds directly into pots outdoors in late autumn or early spring, allowing natural freeze-thaw cycles to condition them.
Sowing the Seeds and Encouraging Germination
Start the stratified seeds indoors roughly six to eight weeks before the final expected frost date. Use a shallow container or seed-starting flat filled with a sterile, fine-textured mix to reduce the risk of disease.
Catmint seeds require light to germinate, so they must be surface-sown rather than buried deeply. Scatter the seeds lightly across the surface of the medium and gently press them down to ensure good contact. If desired, apply a dusting of fine vermiculite or a thin layer of soil, no more than 3 millimeters deep.
Maintain the containers in a warm environment, ideally with a soil temperature consistently between 18°C and 27°C (65°F and 80°F), often requiring a heat mat. Supplemental light from fluorescent or LED grow lights positioned just above the containers will produce stronger seedlings than a south-facing window alone. Keep the medium consistently moist using misting or bottom-watering; sprouting usually occurs within seven to twenty days.
Caring for Young Seedlings and Hardening Off
Initial Care
Once the plants emerge, maintaining proper moisture levels is paramount. Bottom watering is effective as it encourages roots to grow downward and helps mitigate the risk of fungal issues like damping off. After the seedlings develop their first set of true leaves, thin them out to ensure sufficient space and air circulation.
Promoting Bushiness
When the young catmint reaches five to eight centimeters in height, gently pinch them back to promote a bushier growth habit. Pinching the main stem encourages the development of lateral shoots, resulting in a denser, more robust plant structure that is less likely to flop over. Continued strong light exposure is necessary to prevent the seedlings from becoming stretched and weak, a condition known as etiolation.
Hardening Off
Before moving catmint outdoors permanently, they must undergo hardening off, a gradual transition process. Over a period of seven to ten days, introduce the seedlings to outdoor conditions for progressively longer intervals each day. Start with a couple of hours in a sheltered, shaded spot, then slowly increase exposure to direct sunlight, wind, and cooler nighttime temperatures. This acclimatization prevents shock and protects the tender, indoor-grown plants.
Transplanting Outdoors and Ongoing Maintenance
Site Selection and Planting
Transplant the hardened-off seedlings once all danger of spring frost has completely passed. Catmint performs best in a spot receiving at least six hours of direct sunlight daily, though it will tolerate some afternoon shade, especially in hotter climates. The plant is adaptable but requires well-drained soil, thriving even in poor, sandy, or rocky conditions.
When transplanting, dig a hole slightly wider than the seedling’s root ball and set the plant in the ground so the top of the soil line matches the surrounding garden level. Proper spacing is determined by the mature size of the specific variety, but generally, plants should be placed 30 to 60 centimeters apart to allow for mature spread and good air circulation. Water the newly transplanted seedlings deeply right away to help settle the soil around the roots.
Ongoing Maintenance
During the first growing season, provide consistent, deep watering until the plants become fully established, which strengthens the root system. Once established, catmint is highly drought-tolerant and requires minimal supplemental watering. Catmint typically does not require fertilizer, as too much can cause weak, floppy growth, with a simple annual application of compost providing sufficient nutrients.
Encouraging Rebloom
To encourage continuous blooming and a tidy appearance, shear the plants back by about one-third after the first flush of flowers fades. This technique is often called the “Chelsea Chop.”