This is one of the handsomest ornamentals we have, and also one of the most baffling at times. Lilacs live on after those who plant them are gone; often they mark home sites where few other traces remain. Plant them in full sun, where they do not have competition from tree roots and shade. Plant in fall or spring. They like any fair, not too heavy, well-drained, alkaline soil. NEVER use manure around them, and do not use commercial fertilizers on soil, as they will grow too tall.
“Own-Root” lilacs are those started from one piece of plant, that is, not grafted, and these are the best to buy because they are not susceptible to graft-blight disease. You can dig up a lilac bush and move it with a large ball of soil and it will continue to bloom. Prune branches back 1/3 after moving.
Age of bloom
Lilacs sometimes start to bloom in three years, but others take up to 14 years. Sooner or later, all will bloom. If an old lilac bush does not bloom, try these tricks:
1. Dig a two-foot ditch around base of plant to root-prune it.
2. Add some super-phosphate (1/2 lb to every 3 ft of ditch) and return soil to the ditch.
3. Thin out some of the suckers and branches at the base of the plant.
Reasons for non-blooming include: severe drought in late summer after buds have been formed; spring frosts will that have injured buds, preventing them from opening; cold winters; and too many suckers at the base, resulting in heavy competition and sometimes no buds.
If your lilacs bear heavily one year, then scantily the next, there’s nothing to worry about. Lilacs are alternate-bloomers, flowering profusely one year but sparsely or not at all the next. Seed pods left on have nothing to do with this habit of bloom. Heavy shade will cause non-blooming, also nearby trees.
Pruning
Keep the center open, cut out dead and diseased wood, prevent suckers from taking over, and if you wish, remove the dead flower stalks. If you cut out the seed stalks, do so before they turn brown. Do NOT cut down too deep, as next year’s flower buds are found there at the base, and if you cut too close, you’ll remove the buds for next year’s show. It isn’t absolutely necessary to remove the old stalks, although it makes the bush more attractive.
Do NOT trim your lilac like a hedge. If you do, you’ll remove the buds. Its flowering is from the top buds of its branches, and any pruning should be done with that fact in mind. Prune lilacs just after flowering. Cut out branches injured by borers or disease.
Pruning old lilac bushes
You can handle old, neglected, overgrown plants by first cutting out the old trunks, at ground level. If you have a lot of wood and don’t want to be too drastic, make your pruning job into a “three-year plan.” That is, cut out one-third of the old wood this year, another third the following year and the final third, a year after that. Cutting out a third each year gives you continuous blooms without that drastic effect.
A tall, uncared-for lilac should be cut back close to the ground to let new growth come up. If all the growth seems to be on top, and lower part is unsightly, better cut the bush back to within a foot of the ground and start all over again.
Sucker growth
Shoots coming up from the base are called “suckers.” An abundance of sucker sprouts is natural. You should select the best of these and cut off the unwanted ones. If suckers ramble all over the place, mow them with a Lawn mower, or dig them up. Transplant suckers and give them to your friends. These will produce the same color as the parent plants. Nothing can be done to prevent suckering. Cut out the majority of suckers as they pop up. If plants are grafted, suckers will come up from the understock, and these should be removed. Grafted plants produce only one main tree, without suckers.
Propagation
You can start new plants from cuttings, started in summer in cold frame. Or you can graft cuttings on privet understock, but the easy way is to dig up suckers (rooted) and plant them. Seeds are used for starting Persian Lilacs, sown in spring. Regular lilacs seldom start new plants from seeds.
Diseases and insects
Bacterial Blight: This will be worse on white varieties. Young shoots are marked by black stripes and leaves appear water-soaked. Flower buds blacken, and flowers grow limp.
Control: Cut out some limbs for air circulation. Cut out diseased shoots and burn. Avoid use of manure or high-nitrogen plant food. Spray bush well with Bordeaux Mix fungicide.
Phytophthora Blight: It resembles bacterial blight, except killing is greater. Sprouts are blackened. This is a wet weather disease. Avoid manure and high nitrogen plant foods.
Control: Cut out and destroy blighted twigs and shoots well below the point showing infection. Dust the area with sulfur and spray with Bordeaux mix. The same fungus attacks rhododendrons, so do not interplant rhododendron and lilacs.
Leaf Blights: This is characterized by severe fungus on lilac leaves, causing irregular shot-hole appearance.
Control: Spray plants with Bordeaux in mid-June, and if season is rainy, give several applications at weekly intervals.
Leaf Spots: Give same treatment as above.
Powdery Mildew: This fungus causes white felt-like patches on leaves. Snails help keep this down by eating spores off the lilac. If you see beautiful etchings on leaves, you’ll know that snails have been feeding on the fungus spores.
Control: Spray with wettable sulfur or a fungicide containing copper hydroxide or neem oil, following package directions.
Wilt Disease and Witches’ Broom: These are fungal diseases and result in foliage (and sometimes shoots) that appear discolored, undersized or atrophied.
Control: Dig up infected shoots and burn.
Ring-spot and mosaic viruses cannot be controlled.
Physiological diseases
Frost Injury: In late spring, young leaves can be injured by the cold. This results in the leaves being torn along the veins in an irregular pattern.
Graft Blight: This occurs when lilacs are grafted on privet because the graft and understock become incompatible. It results in discolored leaves that may appear to have dead spots on them. “Own roots” lilacs are those not grafted (started from cuttings or suckers) and are best to buy, as they are not susceptible to graft blight disease.
Lilac Borer: Look for holes in branches and sawdust on the ground. Borers are pure white.
Control: Try poking wire into the entranceof the holes, or apply a product containing chlorpyrifos or permethrin according to package directions. Read product labels very carefully to be sure it is intended for lilac-ash borers, and follow all the manufacturer’s instructions. The borers’ life cycle limits the times at which the insects are vulnerable to pesticides, however, so you may want to consult an expert. Removal of affected branches may also be necessary.
European Hornets & Yellowjackets: These hornets will remove a strip of bark and girdle the tree to feed on sap from the wounds. They use the bark to build nests in tree cavities, rafters of buildings or even underground.
Control: Locate the nest. Ideally, hornets are dealt with after cold weather sets in in the fall, because they have difficulty moving or flying in the cold and can even become completely immobilized at 40 degrees or less. If the problem requires immediate solution, wait until evening and use a commercial hornet spray. Use caution, as they can be very aggressive, and follow all package directions for the product you use.
Lilac Leaf Miner: Egg laying starts in early June. After pupae emerge from the ground, and morph into moths, the adults mate. Females lay tiny eggs on the undersides of leaves. Then, once hatched, caterpillars feed and spin webs around curled leaves, skeletonizing them.
Control: If infestation is light, remove affected leaves and burn. If the eggs or caterpillars are too numerous to take care of by removal of affected leaves, use a commercially available product containing dimethoate. This should, however, be a last resort as it is toxic to honeybees and birds. Follow all of the manufacturer’s directions.
Scales: Seven species of this insect live on lilacs.
Control: Spray plants in early spring with lime-sulfur, or use a dinitro dormant spray. During the dormant period, horticultural oils can also be applied. To treat active infestations, use malathion, acephate or chlorpyrifos around mid-May, when the scales are in the crawler stage. Repeat in 2-week intervals. Again, these insecticides can be toxic to bees and other non-target species. Always follow package instructions. |
