Lilac Culture – Hints from Highland Park

Since fall planting is considered to be an important factor in the future development of good shrubs in areas like the Rochester, New York, climate, additions to the world-famous lilac collection at Highland Park are planted in that season.

Usually this is done after the fall rains, during late September or early October when soil conditions are ideal and there is time for plants to become established before cold weather. Planting is the responsibility of the nursery crew which is also in charge of propagation and knows the history of each plant in the collection.

For replacement needs and to increase the collection, budding is done in July and grafting on young privet understock in the winter months. In either case, care is taken to start plants on their own roots as soon as possible.

With grafted stock, privet under-stock is removed at the time the plants receive their final shift in the nursery, and new plants from outside sources are inspected to ascertain if they are on their own roots before they’re set in the nursery row where they stay two years before taking their place in the collection.

Young lilacs are moved to their permanent locations, a few at a time, with bare roots carefully protected against exposure to drying by sun and wind. They are set in ground previously enriched with organic matter in the form of well-rotted manure and leafmold. Care is taken as they are planted that no air pockets form because, unless the soil is nicely watered in to settle it, this will occur. The last detail is important and may mean a poorly leafed shrub that needs two years to establish itself instead of a husky, thriving shrub that does well the first year after planting.

But for the removal of weak growth and crossing branches, little pruning is done at this time. And, it has not been found necessary to stake newly-planted shrubs except to shield those under 4 feet tall from the admiring crowds at “Lilac Time.” Immediately a small lilac is secured in its place, a cup-shaped depression is made around its trunk and filled with leafmold to insure adequate moisture and protection of its roots during the first year.

Thereafter, the cultural program followed is simple but precise. The renowned collection is well located on a south slope of a hill composed of gravelly, well-drained soil with a non-acid reaction. It is exposed to full sun at all times. This is an advantage except during the hot months of a dry summer when watering becomes necessary, for although lilacs will not tolerate stagnant water at their roots caused by poor drainage, they demand sufficient water to stimulate and carry on their new growth during the summer months.

Because of competition for food, other plants are not placed close to the lilacs and although they do not require a great amount of nourishment, they should have an occasional application of complete fertilizer at two year intervals.

Highland Park lilacs used to be mulched with well-rotted manure and leaf mold every other year but due to the limited supply of aged manure, a commercial organic fertilizer was substituted many years ago.

Under the feeding program the trees are given a complete organic fertilizer, cultivated into the top few inches of soil in early spring, the rate of application varying with size of shrub. In addition to this, some sort of organic material is also worked into the soil occasionally in order to retain some moisture in the gravelly loam which drains so rapidly. Over-fertilizing is, of course, avoided as it results in heavy, woody growth and fewer blossoms.

Two other factors help produce the display the public travels from far and wide to view: cultivation and removal of faded blossoms. From early spring until late fall, the area around the base of the plants is continually cultivated, but lightly so that roots at the surface are not disturbed or damaged. Cultivation tends to cut down competition for food and helps to reduce the evaporation of moisture.

Development of larger blooms also depends somewhat on the removal of all faded ones immediately while the stem is still green. It has been found that as soon as flower stems turn brown and seed pods begin to form, it takes much longer to remove the faded flowers. Because the Highland Park staff is not large enough to rush this job through, other park help is called in.

by M Wight

Related Articles Of Interest:

• The Tree Lilac
• Dwarf Korean Lilac – Attractive Shrub with Grace, Fragrance and Beauty
• Planting Trees Correctly – The Steps
• Canterbury Bell – From the Wills Garden Series