Culture Notes
Ivory Silk was chosen as a 1996 Gold Medal Plant by the Pennsylvania Horticultural Society for being a plant of exceptional merit, but underused in landscaping. Ivory Silk is tolerant of urban conditions, growing in poor, clay or alkaline soil. It tolerates high soil salt concentrations originating from de-icing salt applications better than many other plants. The gorgeous flowers are most showy and prolific when the tree is located in full sun with good drainage. Plants in partial shade can be infected with powdery mildew which can cause some defoliation. It is perhaps the most pest-resistant Lilac, but that does not mean it is pest-free. Regular irrigation during dry spells help make this a pest-resistant tree. Pollen bothers certain people.
Trees can be pruned to a short single leader for use along streets or to provide clearance close to a walk or patio. Be sure to clear all turf away from beneath the branches to reduce competition with turf. Remove some branches so they will not touch each other. Remove some secondary branches from main branches (especially those toward the end of the main branches) if main branches have included bark. This reduces the likelihood of main branches splitting from the tree later when it has grown to become an important part of the landscape. Locate the tree properly, taking into account the ultimate size since the tree looks best if it is not pruned to control size. Pruning should be completed after flowering and by late spring to ensure next year's flower buds are not removed.
Tree establishment specifications
Choose good quality trees for planting. The most common cause of young tree failure is planting too deep. In most instances, the point where the top-most root in the root ball originates from the trunk (referred to as the root flare zone or root collar) should be located just above the soil surface. You may have to dig into the root ball to find the root flare. If there is nursery soil over this area, scrape it off. Never place ANY soil over the root ball. The planting hole should be at least twice the width of the root ball, preferably wider because roots grow best in loose soil. In all but exceptional circumstances where the soil is very poor, extensive research clearly shows that there is no need to incorporate any amendments into the backfill soil. Simply use the loosened soil that came out of the planting hole. Simply planting with the topmost portion of the root ball slightly higher than the surrounding soil might still install the tree too deep - be sure to locate the root flare.
Weed suppression during establishment is essential. Apply a 3-inch thick layer of mulch to at least a six-foot diameter circle around the tree. This area should be at least two feet in diameter for each inch of tree trunk diameter and maintained during the establishment period. Apply a thinner layer of mulch directly over the root ball but keep it at least 10 inches from the trunk. This allows rainwater, irrigation and air to easily enter the root ball and keeps the trunk dry. Placing mulch against the trunk and applying too thick a layer above the root ball can kill the plant by oxygen starvation, death of bark, stem and root diseases, prevention of hardening off for winter, vole and other rodent damage to the trunk, keeping soil too wet, or repelling water.
Regular irrigation after planting encourages rapid root growth that is essential for tree establishment. Trees provided with regular irrigation through the first growing season after transplanting require about 3 months (hardiness zones 9-11), 6 months (hardiness zones 7-8), or one year or more (hardiness zones 2-6) per inch of trunk diameter to fully establish roots in the landscape soil. Trees in desert climates may take longer to establish. Trees that are under-irrigated during this establishment period (and most trees are) often require additional time to establish because roots grow more slowly.  Be prepared to irrigate through the entire establishment period, especially during periods of drought.
Irrigation also helps maintain and encourage the desirable dominant leader in the tree canopy on large-maturing trees. Instead of a dominant leader, trees that are under-irrigated during the establishment period often develop undesirable, low, co-dominant stems and double leaders that can split from the tree later.
Unlike established plants, which do best with deep, infrequent irrigation, research clearly shows that recently transplanted trees and shrubs establish quickest with light, frequent irrigation. For trees planted in spring or summer, provide one (cooler hardiness zones) to three irrigations (warmer hardiness zones) each week during the first few months after planting. Daily irrigation in the warmest hardiness zones provides the quickest establishment. Following the initial few months of frequent irrigation, provide weekly irrigation until plants are fully established. With every irrigation, apply one (cool climates) to two (warm climates) gallons of water per inch trunk diameter (e.g. 2 to 4 gallons for a 2-inch tree) over the root ball only. In most landscapes that receive more than 30 inches of rain or irrigation annually, if the mulch area is maintained weed-free, irrigation does not need to be applied outside of the root ball. Never add water if the root ball is saturated.
In cooler hardiness zones, in all but the driest years, irrigation of spring- and summer-planted trees usually can be discontinued once fall color has begun. Irrigation of fall planted trees, however, should be continued until foliage has dropped from the deciduous trees in the region. In warmer climates, irrigate fall-and winter-planted trees as described for the spring- and summer-planted trees.
In drier, desert climates there is benefit to be gained from applying additional irrigation outside of the root ball area. This is best done by making a large diameter berm four to six inches high, then filling it with water so it percolates into the soil. For the first two years, irrigate twice each week through the spring, once per week in summer provided monsoons arrive, and twice each week again in fall if it remains warm. Taper off watering to once or twice each month in winter and resume twice weekly next spring. For years three to five, water twice per month in spring, summer, and fall and once or twice per month in winter. During years five through seven, water once every three weeks in warm weather and once every six weeks in winter. After this, the drought-tolerant desert trees should be able to survive on natural rainfall.
Trees with good, strong structure need no pruning at planting, except to remove broken twigs. Do not remove branches to compensate for root loss - research has shown that this can be detrimental to establishment.
Pests, Diseases and Damaging Agents
Pests: If properly located on an appropriate site, there are few problems. Lilac borer larvae tunnel in the branches, causing wilting, particularly on drought-stressed trees. Lilac leaf miner tunnels in the leaves in early summer. Scales are most often found infesting the lower stems and often blend in with the bark.
Diseases: Usually free of serious disease. Bacterial blight is most serious on white flowered selections. Phytophthora blight kills stems to the ground. Leaf blotch causes zoned, brown spots. Many fungi cause leaf spots.  Powdery mildew can coat the leaves with white powder, although this cultivar is considered resistant. Verticillium wilt causes wilting and premature leaf drop. The disease may kill one, several or all the branches. Try fertilizing regularly to help prevent diseases. Bacterial crown gall causes round, warty galls on the stems near the soil line.Â