Japanese lilac, known botanically as Syringa reticulata, is a species of flowering tree or large shrub that throws warm white blooms in late spring and early summer. Japanese lilac is hardy in USDA zones 3 through 7, thrives in a full sun to partial shade exposure and evenly moist soil. They are grown as specimen landscape plants, in borders and for cut flowers. Plant your Japanese lilac in the spring or fall to minimize stress on the tree.
Prepare a planting hole in nutrient rich and well drained soil that is twice the width and half again as deep as the lilac's root ball. Till up the soil on the sides and floor of the hole to loosen it, making new root penetration easier. Amend the planting hole and soil with compost or well aged manure to boost the nutrient quotient. When planting multiple lilacs, allow an interval of at least 15 feet up to 25 feet to accommodate the trees' spread at maturity.
Slide the tree out of its nursery pot gently while leaning the pot onto its side. Place the plant in the prepared hole so that it sits at the exact same depth in the soil as it was in its nursery pot. For balled and burlapped trees, ensure that the top of the root ball is level with the surrounding ground soil.
Replace the soil around the root ball with the added compost and tamp down with your hands or heels to collapse any large air pockets. When the hole is filled halfway with soil water in and allow the water to percolate down into the soil before filling in the rest of the soil. With the excess displaced soil, create a 3-inch high moat around the root ball to act as a catch for water. Fill the moat with water and allow it to percolate down and refill it once more.
Mulch the base of the tree with an organic material to feed the soil and reduce moisture lost to the atmosphere. Use cocoa hulls, compost, leaf mold or shredded bark in a 2-inch thick doughnut-like blanket laid from a foot out from the trunk to the drip line of the tree.