Perennials are plants that come back year after year in the garden, offering seasonal flower, foliage and fruit interest throughout the year. However, the costs can add up when collecting your favorites for the perennial border. Why not save a few bucks through propagation? Perennials can be propagated in three primary ways: seed, cuttings and division.
Growing Perennials From Seed
Although plant species come true from seed, not all named cultivars do. Collect seed in the fall, and plant it in early spring. To collect seed, clip dried flowers from the plant, and place them in a paper envelope. Write the name of the plant and the date the seed was harvested on the envelope, then store it in a cool, dry place during the winter.
In early spring fill a clean seed tray with fresh seed-starting soil mix and water it well. Remove the flower heads from the envelope, and rub them gently between your palms over a piece of white paper. The seeds will fall onto the paper. Separate the seeds from the chaff, which includes the seed covering and small pieces of leaves and stems. Return the seeds to the envelope for easy planting. Sprinkle seeds over the surface of the damp soil. Cover the seeds with only a light dusting of potting mix.
Label the seed tray, listing the type of seed sown and the date planted, then mist the flats with water. Place the flats in a warm, bright spot. Check them daily and keep the potting mix moist but not soggy or wet. In a few days to a few weeks, depending on the plant, you should begin to see some growth.
After seedlings have formed about two to three sets of leaves, gently lift them out of the seed tray, then carefully separate and transplant them into small pots filled with fresh potting soil mix. Take extra care to minimize root disturbance. Water seedlings immediately after planting. Keep plants well-watered until they are ready to go out into the garden.
Growing Perennials From Cuttings
A good way to propagate named cultivars is from cuttings. Tip cuttings should be taken in early summer. To do this, take a cutting about four to six inches long at the end of the stem; make sure the cutting is soft, not woody. Soft cuttings are much easier to propagate than woody ones.
Fill a shallow container with a mixture of peat, vermiculite and perlite or sand and peat, moisten and set aside. Remove all but two or three leaves at the tip of the cutting. If it's a large-leaved plant with leaves longer than two inches, cut each remaining leaf in half. Dip the cut end of the stem into rooting hormone, and make a hole in the damp soil mix with a chopstick or a pencil. Place the cutting carefully into the prepared hole. Take several cuttings to improve your chances of getting a viable one.
Cover the flat with a clear plastic bag or lid to keep in the humidity, and use straws or chopsticks to prevent the bag from touching the plants. Place cuttings in an area with bright indirect light and warm temperatures. Keep the soil mix damp, and when you see new growth, you'll know you've been successful. Don't transplant the new plants into the soil until they're well established and it's evident that roots are supporting the new growth. If you can see roots growing from the bottom of the flat, the cuttings are ready to be transplanted to individual pots. Grow them on in pots until they are well-rooted and then transplant them into the garden.
Many perennials, such as blue star (Amsonia) and comfrey (Symphytum), can also be propagated from root cuttings. Cut fleshy three-inch pieces of root, and lay them horizontally in a rich potting medium. Cover the roots lightly with soil, and water them. This method works well for fibrous-rooted plants such as agapanthus and daylily.
Note: When propagating perennials, avoid rooting cuttings of plants that are patent-protected as that is prohibited by law.
Since most perennials grow wider every year, they eventually start to die out in the middle, resembling more of a ringlike than a clumping growth habit. The process of rejuvenating clumping perennials by digging out pieces of it is called division. When dividing a plant, it is sectioned off into separate pieces, essentially creating more individual plants that can be transplanted elsewhere.
The ideal time of year to divide most perennials is in the spring when a plant is breaking its dormancy and has begun a period of active growth. The plant has the energy and time allowed over the growing season to develop new roots and top growth. However, some plants can be divided in the fall.
To divide your perennials, first cut back top-heavy plants by one-third to one-half; this prevents the plant from focusing its energy into maintaining the foliage or flowers on top but instead focuses the energy towards root production. With a shovel, lift the plant out of the ground and cut the plant into several sections that have top growth and roots attached. For densely growing plants such as ornamental grasses or perennial hibiscus, it may be necessary to use a saw or knife to cut the plants into different sections. Transplant each section into a site similar to its previous location. Water the transplant thoroughly and keep the plant well watered as it establishes itself in its new location.