What causes lilacs to bloom twice a year?

Lilacs are a beloved spring flowering shrub, known for their fragrant blooms and bright colors. Many gardeners have experienced the disappointment of seeing their beautiful spring blooms fade away only to be replaced by bare branches during the summer months. But did you know that there are some varieties of lilac that can bloom twice a year? In this article, we’ll explore what causes these plants to bloom twice a year, so you can enjoy their beauty for more than just one season!

What are Lilacs?

Lilacs (Syringa spp.) are deciduous shrubs with highly fragrant flowers that come in various shades of purple, pink, white and blue. They are native to the northern hemisphere and thrive in USDA Hardiness Zones 3-7 depending on the variety selected. Lilacs reach heights of 8-15 feet tall and spread 4-8 feet wide at maturity with an upright, vase-shaped form when unpruned or trained as a standard tree form when pruned correctly. They can be found in gardens around the world due to their ease of care and long-lasting blooms which make them an excellent choice for any landscape design!

What Causes Lilacs to Bloom Twice a Year?

The secret behind why some varieties of lilac can bloom twice in one year is due to the plant’s response to certain environmental cues such as temperature, daylight hours, water availability, soil fertility, and pruning practices which all play an important role in when the flower buds will set and bloom on these plants! Let’s take a look at each one!

Temperature and Daylight Hours

One of the most important factors that triggers lilac flower buds is temperature changes throughout the seasons which is why it blooms in springtime shortly after winter has passed and again in fall when temperatures start cooling down again. Additionally, the number of daylight hours during winter can also affect when flower buds will set or open on these plants!

Stressful Conditions

Lilacs may also bloom twice if they experience stressful conditions such as drought or cold temperatures during their growing period which puts them into a dormant-like state where they may produce flower buds but won’t actually open until cooler temperatures arrive in fall which triggers them to bloom again! This phenomenon is known as ‘vernalization’ and is often seen with plants that need cold temperatures for dormancy such as apples or peaches!

Water Requirements

As with any plant, water plays an important role in how it will grow and bloom so it’s important to provide your lilac with ample moisture throughout its growing season by watering it deeply once every week during times of drought or heat waves to ensure it gets enough moisture for healthy growth and blooming!

Nutrient Requirements

Just like water, nutrients are essential for healthy growth so make sure your lilac is getting all the nutrients it needs by fertilizing three times per year with an organic fertilizer such as compost or manure tea applied at each stage of development from late winter/early spring through summer into fall before winter arrives again!

Soil Conditions

Lilacs need well-draining soil that is rich in organic matter so make sure to test your soil before planting your shrub and amend accordingly if needed with compost or aged manure prior to planting for best results! Additionally, mulch around your shrub will help keep roots cool during summer months while still allowing adequate drainage!

Pruning & Deadheading Practices

Pruning should be done right after flowering has finished each year (in late spring/early summer) as this will encourage new growth & more flowering next season while deadheading spent flowers throughout the season will help ensure there will be plenty of blooms come springtime each year!

Fertilization Practices

Fertilizing your lilac should be done 2-4 times per year depending on variety & climate zone with a balanced fertilizer such as 10-10-10 applied at each stage from late winter/early spring through summer into fall before winter arrives again! This will help ensure your shrub has all the nutrients it needs for healthy growth & abundant blooms each year!


Lilacs can be enjoyed not only once but twice a year if cared for correctly by providing adequate water & nutrients along with proper pruning & deadheading practices & timely fertilization applications based on variety & climate zone! With these tips in mind you’ll have no trouble enjoying this beloved shrub for years to come so get out there & start gardening today!

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