Lilac Question & Answer: Scale Insects | Not Blooming | Transplanting | More

Lilacs are beautiful bushes and trees for the landscape. Below are questions and answers on a variety of lilac topics readers experience.

Check out our article on Lilac Bush Care 

Blooming Lilac bushPin

Lilac Bush Covered In Scale

Question: We have a lilac bush in our yard, covered with scale. We sprayed last year without success. To save this bush, should we cut it back to the ground and disinfect the soil? Some of our other trees, especially the elms, had a great deal of this scale. What do you recommend? SF, Nebraska

Answer: Branches of the lilac heavily infested with scale will die, and the health and vigor of the entire shrub are impaired. Neither pruning nor soil treatment will control the scale. Use a dormant spray as soon as you discover scale insects, spraying not only the lilacs but all shrubs in the vicinity of the lilacs.

This dormant spray should be a miscible oil spray such as Volck oil, diluted to 1/3 pint of Volck to a gallon of water. After the blooming season passes, spray the plants with Malathion using one teaspoonful to a gallon of water. Malathion will destroy immature scale in the crawling stage.

Question: My lilac seems to have scaled all over it. Then something made holes down the center of the stalks. What can I do for them?

Answer: To control scale and borers on the lilacs, spray them in the early winter and again in late winter with Volck, one part to 40 parts of water. Cut out at once all canes that show injury.

When Do You Transplant French Lilac Bushes?

Question: I would love to transplant my French lilac bush. It is too crowded where it now grows. When is a good time to transplant? JS, Ohio

Answer: Move or transplant French Lilac as soon as the frost is out of the ground and the soil is in good working condition. Move it with as much dirt as possible. It will require severe pruning, which will cut away most of the bloom for the ensuing year.

Will New Lilac Shoots Flower?

Question: About six years ago, we chopped off an old lilac bush that had very few flowers. Since then, there have been several young shoots. If I move some of the shoots, would they flower for me? CR, Iowa

Answer:  The sprouts coming up from an old lilac bush may be dug, replanted, and should bloom, unless the bush was originally a grafted plant. In that case, the sprouts may not be lilacs but rather privet plants. If the leaves on the sprouts are lilac leaves, quite different from privet leaves, the plant should bloom if planted in full sun.

How To Start New Lilacs From Old Bushes

Question: We have a very old lilac bush and would like to know how to start some new ones. It does not send up new starts. PW, Ohio

Answer:  Lilacs are usually started from cuttings. Start them from either softwood or hardwood cuttings. 

Softwood cuttings – the greenwood – take in May of the current season’s growth, root quickly. The cuttings should be 4″ or 5″ inches long and set in sand in a closed case or frame. They will soon root in a closed humid atmosphere. 

Hardwood cuttings are taken after frost. Bury cuttings about 8″ inches long, in the sand in a cool frost-proof place, and left until spring. By then, the ends of the cuttings should be callused.

Planted outdoors in April, with about one inch of the tip above the ground, they will soon start to root. In a short time, leaves will appear, and growth should continue rapidly.

Does Picking Sprays Of Lilacs Stop Next Years Bloom?

Question: I have been told that if I pick sprays of lilacs when in bloom I will be picking off next year’s bloom. Is this so?

Answer: Cutting lilac blooms will in no way interfere with their blooming the following year. Late summer or fall pruning will destroy the bloom, but the removal of wood at blooming time or shortly after encourages new growth, which forms bloom buds for the next year’s flowers.

Related: Details on growing Dwarf Korean Lilac

I Have A Healthy Looking Lilac But Few Flowers?

Question:  I have a healthy-looking lilac tree, full-branched, and about ten feet tall. Last year it had only about ten flower clusters and the same this year. How could I encourage more flower production next spring? WG, Mass

Answer:  A liberal sprinkling of bonemeal scratched in this fall, or superphosphate in spring, should be helpful. Remove any weak inside growth.

Question: I have a white lilac bush about three years old, which has big healthy leaves, but it never flowered.

Answer from Keith: The bloom buds for next year’s lilac bloom form during this season’s growth. By fall, the bloom buds should be ripe and ready to push forth and bloom in the spring. 

If they do not form, the variety of lilac is at fault, the soil is too light and rich, or plant suckers at the base of the plant are robbing old wood of the vitality required to form bloom buds. 

At frost time, if there are no heavy fat terminal buds, there will be no bloom. Remove the bush and replace it with a new one. Summer or fall pruning will also destroy bloom buds.

What Is a Good Lilac Fertilizer?

Question: What is a good complete fertilizer to use on lilacs?

Answer: Use a 5-8-7 fertilizer, spreading 1-2 cupfuls in a wide ring around each shrub.

What Does My Lilac Have Brown or Shriveled New Growth?

Question: The new growth on one of my lilacs is rather brown and shriveled, looking, and the same symptoms are beginning to appear on the foliage of my other lilacs. FT, Silver Creek, NY

Answer:  It sounds as though your lilacs are infected with a blight disease. Try spraying with a Bordeaux mixture or other copper fungicide in early June.

Meanwhile, gather up and destroy the old leaves. Lilacs grafted on privet sometimes get a blight, for which the only remedy is to destroy affected plants.

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