The Japanese lilac tree, or Syringa reticulata, is classified as both a large shrub and a small tree. This ornamental has creamy white flowers that fill the summer air with their abundant floral fragrance. As its name suggests, the Japanese lilac is native to Japan. It grows abundantly in cool climates but can suffer in hot climates. USDA planting zones 4 to 7 are ideal for growing and propagating a Japanese lilac. While propagation from seed is possible, seeds do not always grow true to the parent tree. Propagation from a cutting is the best way to reproduce your Japanese lilac.
Take a 4- to 6-inch softwood leafy cutting in the spring late spring to early summer. Use a pair of sharp pruning shears and make the cut at a 45-degree angle. Chose a cutting that has green, supple wood and at least 2 leaves on it.
Fill an 8- to 10-inch planting pot with equal parts sand and potting soil or purchase a rooting mix from your local garden store.
Roll the bottom inch of your lilac cutting in hormone rooting powder for soft cuttings. Hormone rooting powder can be found at most nurseries. Avoid formulas for ripe or hardwood cuttings as they will be too strong for the tender green wood.
Make a 2-inch deep hole in the center of your planting pot; you can use a pencil, dowel or your index finger.
Place the cutting in the planting pot and press the soil down around it. Water the pot until the soil is evenly damp.
Place a clear plastic bag over the cutting and secure the top of the bag around the rim of the pot with a rubber band or string. This will create a mini greenhouse and will keep the environment around your cutting humid while it develops a new root system.
Put the cutting in an area that gets dappled shade; avoid full sun at this stage because it will poach the tender cutting in its greenhouse.
Check the soil in the pot every few days; the soil should be damp but not saturated. When the soil begins to feel slightly dry on top, remove the bag and water the cutting. Replace the bag when you are finished watering.
After four to six weeks, you will notice tiny white roots just below the surface of the soil at the edge of the pot. When this occurs, you can transplant your cutting outside.
Dig a hole that is large enough to accommodate the root ball of your newly rooted cutting. Chose an area that gets full sun.
Turn the pot onto inside and gently wiggle the cutting loose. Place the cutting into the hole so that the base of the stem is level with the soil. Fill in around the root ball and water the area so that the soil is damp to a depth of 8 to 10 inches.