Cones of fragrant lavender, pink or white flowers make lilacs (Syringa spp.) stand out in the spring garden. The deciduous shrubs grow in U.S. Department of Agriculture plant hardiness zones 3 through 7, depending on the specific variety. You can start a new lilac from softwood cuttings from an existing healthy plant, but the proper timing and rooting method is crucial for success.
Cuttings don't need a lot of nutrients to take root, but they do need a sterile environment with moist, well-draining media. Disinfect containers and tools by soaking them in a solution of 1 part bleach and 9 parts water for 30 minutes, or give everything a thorough wipe down with a cloth soaked in isopropyl alcohol. A 6- to 8-inch container with bottom drainage holes has enough room to start several cuttings. Although any sterile potting media works, a media made from equal parts sand and peat moss is sterile and holds the appropriate amount of moisture. Water the media until the excess moisture drains from the bottom and the media feels evenly moist.
A Clean Cut
Timing is crucial when taking the cuttings. Select stems from new growth after the flowers wilt, but before the tender new growth at the stems tips grows longer than 6 inches and begins to turn woody. Find new wood that's still between 3 and 5 inches long but snaps instead of bends, otherwise the wood is too green and won't root. Cut the stem so it has two or three leaf nodes, or buds, making the cut at a slight angle with the disinfected shears.
A rooting hormone encourages the cutting to send out roots more quickly. You can use any commercial rooting powder as long as it contains the chemical auxin at the rate of 500 to 1,250 parts per million. Simply dip the cut end of the stem in water to moisten it, and then coat it thoroughly in the rooting powder. Poke a hole in the media with your finger and stick the cut end into the prepared media. Firm the soil around the cutting so the stem stays upright on its own.
Putting Down Roots
Moisture control allows the lilac to root quickly without falling prey to fungal problems. Set the pot in an area with bright but indirect sunlight. Keeping the soil moist, but not soggy, helps the lilac root. Mist the stem with water three times a day and maintain temperatures near 85 degrees Fahrenheit. Setting the pot on a plant heat mat to maintain bottom heat near 70 F also speeds rooting. Lilacs usually form roots and begin putting on new growth within three to six weeks. Transplant your cuttings outside in late summer or the following spring, planting them in a sunny, well-drained garden bed.