Growing Garden Lilacs

There are many things to consider when choosing a lilac. Your first will likely be color of flowers and placement in your landscape. They are important, but climate is more so if you live at the edges of the best lilac areas.

The lilac is the only fabulously varied shrub that gives the advantage of great choice to gardeners who live with long cold winters. Most lilacs require about 1,000 hours below 50 degrees F (10°C) to trigger the development of their flower buds, and they'll put up with far more cold weather than that. The hyacinthiflora lilacs and broadleaf lilac (S.oblata) are tough enough, but because they bloom early, their buds can be damaged by late frost. It's important, especially at the colder edges of the zones of lilac hardiness, to plant your choices on high ground, not in frost pockets where cold air can rest.  Most lilacs need a cold winter to bloom. Syringa x chinensis, S. x hyacinthiflora, S. pubescens subsp. patula and some cultivars of S. vulgaris will bloom in temperatures between 10 to 20°F(-12°C to -6°C), although mildew can be unsightly where summers are humid.

When to plant

Lilacs are best planted in spring, as soon as the soil has thawed and is workable; don't plant them in ground that is still soggy from melted snow. The favored planting time is the second half of April. This early planting allows the roots to begin growing before summer's heat and drought. Spring is also when the best selection of lilacs is available and when they will likely arrive if you are having plants shipped. Don't leave planting too late, however. After the soil temperature drops to 41 degrees F (5°C) in fall, root growth is so slow that the plant will not become established before winter.

Lilac requirements

Lilacs need sun, at least four hours a day. The more, the better in northern gardens, although in more southerly gardens, the higher and brighter the sun shines, the more appreciative lilacs are of partial shade. A bit of shade will also slow the fading of pinks and the darker colors.

Lilacs need space. The usual distance allowed between shrubs in botanical gardens and arboretums is 6 feet (1.8 m). If you are growing your lilac in a lawn and use a riding mower, 10 feet (3 m) is better. The only time closer planting is advised is for a hedge.

Lilacs need well-drained soil. With the exception of the Himalayan lilac (S. emodi), they will die in waterlogged ground. If you must plant where the soil is not well drained-if water tends to puddle or the ground usually feels damp in spring and cracks in summer-raise the bed before you plant the lilac.

Provided it is well drained, virtually any soil will do, from slightly acidic to quite alkaline. Poor soil suits lilacs. In soil that is too rich or too heavily fertilized, they may not bloom. The lilac's legendary need for alkaline soil comes from tolerance-they survive on virtually bare limestone-rather than preference. But soil that is very acidic, below pH 6.5, should be amended with half a cup (125 mL) of horticultural lime mixed into the hole at planting time and spread around the base of the plant every spring.

Planting lilacs

Once you've located a good position-in full sun or slight shade, with well-drained soil and plenty of elbowroom in an aesthetically pleasing spot, remove all sod and stones from the planting area, and dig a hole about 50 percent wider than the root ball; save the removed soil. The hole should be deep enough that the lilac can be planted at the same depth as before, with all roots buried. Fill the planting hole with water just before you plant your lilac.

Potted plants must be removed from their pots before planting. Even fiber pots should be cut or torn away. Sometimes a plant will slide easily out of the pot, but don't lift it by the stem or pull it hard because you may tear its roots. Press the sides of the pot to loosen the  rootball and then hold the pot at an angle or upside down while you ease the plant out. If the shrub or tree is large and especially if it is root bound, you may need to step on the side of the pot to loosen its grip. Gently slide the plant out of the pot and lift it by putting your hands under the rootball. You may need help to keep the stem vertical while you shovel soil around the roots.

It is usually the larger lilacs that are balled and bur lapped, and at least two people are needed to handle them. Burlap may be treated to resist decay, so it should be removed. Untie the burlap around the stem, lift the plant by the burlap and slide the plant into the hole. Remove any labels, twine or wire.

When the lilac roots are in position in the planting hole, fill around and over them with removed soil. Do not add fertilizers or additives such as peat moss, as the tree will fare better in the long run if it is not planted in a pocket of superior soil, which could discourage root growth beyond the pocket. Firm the soil around the roots with your foot, then water deeply. A bucket of water per plant is about right. Don't press the wet soil down. Stake for the first year only if the planting site is very windy.

Mulching

Whether or not to mulch is a matter of preference. Mulching keeps weeds down and holds soil moisture in. It helps prevent girdling accidents from mowers and trimmers. It looks attractive if it extends as far out as the width of the mature plant. The usual labor-saving practice is to apply the grass killer 2,4-D (Roundup) directly to the circle of sod around the stem in summer or fall and immediately spread the mulch. An environmentally friendly alternative for the home garden involves spreading several layers of newspaper over the sod, then covering them with mulch. The newspaper will compost in a season, and the sod underneath will die. An alternative to bark mulch is a groundcover, a living mulch.

For the first month, water the lilac thoroughly once a week if the weather is dry. For the remainder of the first summer, water every couple of weeks during dry weather. Lilac roots are shallow but can be encouraged to grow downward with deep watering. In the following seasons, a lilac should not require any watering unless there is a prolonged drought.

Grafted vs. own-root

If your lilac has been grafted, you will see a slight swelling, a sort of "knee joint," above the roots. The bark may look different above and below this joint. Grafting is the joining of your desired lilac cultivar (called the scion) to another type of lilac used for its roots (called the stock). When you plant the lilac, the graft should be below ground to encourage the scion to put out its own roots. Grafting of lilacs, once very common, is no longer favored for several reasons. For one thing, the rootstock is a different variety from the scion. It may be less winter-hardy or somewhat incompatible. Should shoots emerge from the rootstock, you could end up with an entirely different lilac. This is one way to determine whether a lilac already growing on your property was grafted. If the shoots arising from below the ground bear the same flowers as the older branches, your lilac was not grafted-or, just as good, has rooted from above the graft. Another problem with grafts is that they present entry spots for borers and for a fungal disease that can cause the quick decline and death of your plant.

Fertilizing

Most garden lilacs-and all wild lilacs-survive with no fertilizing at all. Lilacs are remarkably self-sufficient and more likely to be harmed by too much fertilizer than too little. If you want to fertilize, hold off the year you plant and wait until the following spring. If you are using a commercial fertilizer, the recommended rate for shrubs is 1 to 2 pounds per 100 square feet (0.5-1 kg per 10 m2) for those grouped in beds, or 0.5 to 1 pound (0.25-0.5 kg) per plant for specimen plants. Use the lower figures in colder areas. Apply the fertilizer lightly around the drip line - the ground directly under the farthest reaches of the branch tips. Fertilize only in spring. Water thoroughly after applying a dry fertilizer.

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