Why Japanese Lilac Tree Not Blooming or Lilac Not Flowering?

Your garden looks fancier when you manage to grow a Japanese Lilac Tree. Their tiny and tubular cluster of blooms alleviates the beauty of the garden. With a wider range of shades between purple and white, the flowers of the Japanese lilac tree are absolute elegance.

But it is a bit unfortunate that for being high-maintenance your Japanese lilac tree might betray by not blooming. So, it will not be surprising if your Japanese lilac tree not blooming in one spring. But obviously, you have all right to ask, why?

Well, there might be a number of reasons for your lilac bush not blooming well or at all. Some of them are insufficient sunlight, improper pruning, late freezes, age of lilac, improper fertilizing, and others.

So, let us cover each reason in detail with the ways of fixing it. Help yourself out by going through the whole article.

Why Your Japanese Lilac Tree Not Blooming – Reasons With Control Measure

Japanese Lilac Tree Not Blooming

1. Inadequate Sunlight

There might be several possible reasons but inadequate sunlight is the most common reason for your Japanese lilac not flowering properly. Japanese lilac trees require direct sunlight for about six hours every day. It allows the lilac to bloom at its best.

Shaded lilacs might grow well but they will certainly not bloom. So, if your lilacs are shaded somehow by other trees or other things then it will stop the blooming process.

Again, the bush itself becomes a shade for the foliage at the bottom. Therefore, foliage near the ground does not get enough sunlight. Consequently, the bush does not bloom on the bottom.

Control Measure

  • Check out the location first where you are going to plant your Japanese lilac.
  • Prune the trees that are creating shade for the lilacs.
  • Thin out the bush to ensure each part of the lilac gets enough sunshine.

However, you might think of transplanting your lilacs in order to place them in a sunny location. But that would not be wise since it may detain the blooming process for an entire year.

2. Inappropriate Pruning

Like any other flower shrubs or bushes, the Japanese lilac tree also acts the opposite if pruning is done inappropriately. Since lilacs bloom on old wood, they form buds in the previous season. Thus, it is important to know when you are getting done with the task of pruning.

If you prune off the bush in the early fall or late summer then there are possibilities you cut off the flower buds as well. As a result, there is no sign of blooms the next year.

Again, pruning lilacs drastically at one time will also cause a delay in blooming. So, maintaining the right methods of pruning is also important.

Control Measure

  • Prune your lilacs when they are done blooming.
  • Pruning should be done depending on the area and its season. However, June is considerable for this.
  • Prune only the old and thick branches.
  • Trim or thin inner branches as well to let the sunlight penetrate.

It is noticed that after the blooms die back lilacs form new buds. So, if your Japanese lilac bush requires hard pruning, do it when they are done flowering.

3. Late Freeze Damages Blooms

Many countries around the world come with this weather. They often show late freezes, especially in April and May. Severe freeze is prone to damage the buds of the Japanese lilac tree.

It can make the entire bush bloomless or very few blooms. However, it might not heart the foliage much. But surely it will deprive you of the view of fragrant flowers.

Control Measure

  • If your area often gets late freezes each year then make sure to plant your lilacs near a building.
  • If you have already planted your lilacs in an open space then you can cover them with a blanket when late freezes come.

Nonetheless, it is a bit tough to determine when the late freeze might show. So, keeping eye on weather forecasting might help. Most of the time it remains only for one night or two. However, instead of a blanket, you can also use garden cover sheets or cloth.

4. Aged Lilac Tree

Transplanted lilac trees take about five to seven years to finally settle and bloom properly. It takes time to get to the mature stage and bloom in a consistent way.

However, younger woods of 5 or 6 years old are considered the best for lilacs to bloom heavily. Unfortunately, when the woods are aged enough their blooming capability gets reduced.

As a result, you do not get your desired number of blooms in the bushes.

Control Measure

  • Pruning is also a solution to this problem. We suggest you go for rejuvenation pruning of the bush.
  • Prune off the dead and old wood instead of young wood.

Long story short, only by pruning in a proper way you can keep your precious lilac tree forever young.

5. Improper Fertilizing and Wrong Soil

It is obvious that the lilac tree also requires some specific and essential nutrient elements to bloom. Hence, many gardeners use fertilizers. Many use too much nitrogen to make their lilac trees greener. But you should know using excessive nitrogen is also a reason for your Japanese lilac tree not blooming.

 Again, you have to determine if the soil where your lilac is planted conserves plenty of nutrients. If the soil already can offer the required nitrogen, then adding nitrogen-based fertilizer again will ruin the plant.

It will inhibit the blooming as well. Yes, you can certainly add nitrogenous fertilizers if the soil lacks them. However, do not forget to determine if it is also able to provide the phosphorous that is required for the lilacs.

Phosphorous induces the process of blooming and also helps the tree to offer flowers consistently. Again, lilacs grow and bloom best in soil that is slightly alkaline.

So, they need a soil pH of about 6.5 to 7.0 to bloom properly. If the tested soil pH shows below 5.5 then you might have to take action.

Control Measure

  • Stop using an excessive amount of nitrogenous fertilizer.
  • If the soil lacks phosphorus, then add phosphorus-based fertilizer.
  • You can also use bone meal in the soil. Bone meal is a great source of phosphorus.
  • Again, you can add Bat Guano or rock phosphate as well as substitutes.
  • Add lime if the soil pH is below 5.5.
  • Finally, adding good compost to mulch the ground around your lilac can also help.

Soil that is rich in the organic matter does not require much fertilizer to grow bushes and flowers. However, if you want to use balanced fertilizers (our pick: Shake ‘N Feed Flowering Trees and Shrubs Plant Food) to take care of the blooming of your lilac trees then make sure you read out the instructions thoroughly.

6. Too Much Water

Indeed, lilacs grow well in moist soil but it also has to be well-drained. It is simply because your Japanese lilac tree does not want wet feet. If your lilacs are failing to flower then they must be getting too much water.

Lilacs are intolerant to excessive water. They even can survive throughout the summer with the water they have deposited during winter. So, even if there isn’t any rain in summer, your lilac tree will manage to bloom somehow. Whereas excessive water lessens the chance of blooming

Control Measure

  • Ensure your lilac tree gets at least a week of hot weather.
  • Do not water the lilacs frequently.
  • Check if the soil is holding up stagnant water.

7. Attack from Pests and Diseases

Borers and some scale insects have been noticed in some area that affects the lilac not flowering. Pests are dangerous not only for the blooms but also damage the entire foliage of a tree. Wood borers attack the tree wood with buds and damage them.

Again, if the tree shows any natural wound, then fungal infections will surely take place. It will also prohibit the growth of blooms.

Control Measure

  • Rejuvenating pruning might help in this case as well
  • Use commercial pesticide or insecticidal soaps if the attack is severe (our pick: Natria 706230A Insecticidal Soap) 
  • In the case of an acute fungal attack, you can use a commercial fungicide(our pick: Bonide 775 Copper Fungicide)
  • Invite beneficial insects to eat up the borers and scales.
  • Or else, come up with some homemade recipes,

# Treat with Neem Oil

Required Materials-

  • Neem oil
  • Dish soap or detergent
  • Water


  1. Take one or two tablespoons of neem oil with one or two tablespoons of dish soap
  2. Mix them in a gallon of water
  3. Pour in a spray bottle
  4. Lastly, apply to the pests

Neem oil contains azadirachtin in it. Thus, it is considered a great organic pesticide. However, you have got to be careful with the usage of neem oil as excessive use of this product might kill beneficial insects as well.

# Spray Rubbing Alcohol

You can simply mix 1:7 part of rubbing alcohol and water in a spray bottle and apply it on the scale insects.

8. Small Container

If your lilacs are planted in a small pot then it will resist the tree to spread properly let alone let them bloom. So, it can be a reason for your Japanese lilac not blooming.

Lilac Tree in pot

Control Measure

  • You must take a larger container to plant your lilac.
  • Make sure the pot comes with good soil without added fertilizer.
  • Ensure enough room for the roots of your lilacs to have greater blooms.

So, these are some major reasons for your Japanese lilac tree not blooming.

Well, there might be some other causes like if the previous winter was warmer than usual then you are unlikely to get any blooms. Cold winter induces blooms of lilac.

Read More

  1. Hollyhock Vs Gladiolus: A Detailed Comparison
  2. Ivory Silk Lilac Tree Problems [With 8 Credible Fixes]


Q: How can I encourage my Japanese Lilac tree to bloom?

Ans: To encourage blooming, make sure the tree is getting enough sunlight, water, and fertilizer. Avoid pruning the tree during the wrong season or excessively.

Q: Can a lack of pruning cause a Japanese Lilac tree to not bloom?

Ans: Yes, if you do not prune your Japanese Lilac tree, it can lead to a lack of airflow and sunlight, which may prevent blooming.

Q: What is the best time of year to prune a Japanese Lilac tree?

Ans: The best time to prune a Japanese Lilac tree is immediately after blooming or in early spring before new growth begins.

Q: How long does it take for a Japanese Lilac tree to mature and bloom?

Ans: It can take several years for a Japanese Lilac tree to mature and bloom, typically around 3-5 years.

How Often Do Japanese Lilacs Bloom?

Generally, Japanese lilac trees show a cluster of blooms during early summer lasting up to two weeks.

When Should I Fertilize My Japanese Lilac Tree?

The best time for fertilizing your lilac tree is in early spring. It helps in the proper blooming of the tree. To get the best result, fertilize after pruning.

Do Lilacs Bloom Every Year?

Yes, mostly lilac bushes happen to bloom every year. However, improper pruning and other environmental obstacles might not let them bloom every year.

Final Word

We have tried to enlist almost all the factors that might affect the blooming of your Japanese lilac tree. However, now it is all up to you to determine which one is the reason for your tree. Sometimes whipping the tree also helps in blooming.

For that, you can use several tools like a rubber hose, broomstick, or any other tools similar to them.

So, if our article comes of any help to you then let us know through your valuable feedback!

James Rivenburg
James Rivenburg
James Rivenburg

James Rivenburg is the founder of plantandpest.com, a passionate gardener with valuable experience and knowledge gained through trial and error. The website has a large community of followers who trust his tips and techniques and have succeeded with his advice. He is always Committed to helping others create a beautiful and healthy garden.

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