Its incomparable fragrance is associated with the long-awaited arrival of spring. Purple, pink, white or bluish, its clustered inflorescences attract all pollinating insects. Easy to grow, the lilac is one of the must-have shrubs in a garden!
To which botanical family does the Lilac belong?
The lilac belongs to the genus Syringa which has about twenty species and is part of the Oleaceae family.
Syringa vulgaris is native to the Orient as is Syringa persica, the Persian lilac, a lesser known but equally fragrant species. The lilac is a deciduous shrub that can reach 1.5 to 7 meters in height depending on the species and varieties.
How to water the lilac?
Once well established in the ground (more than 3 years old), lilacs can withstand a few dry spells, especially when it comes to the Syringa vulgaris type, as the cultivars are more sensitive to water shortages.
In the years following planting, the soil must remain cool throughout the summer. Mulch it copiously to preserve its humidity. Beware of winter drought in southern regions on recently planted plants!
In pots, the substrate should never dry out completely during the summer season, but should not remain soggy. In winter, reduce watering to the strict minimum.
How to grow lilac in the ground?
Lilac is not a difficult shrub to grow as long as the soil is well drained. Stony and chalky soils do not discourage it, on the contrary! It appreciates a very sunny exposure but can tolerate half-shade in southern regions.
The typical species Syringa vulgaris tolerates drought much better than its cultivars, which need always fresh soil, especially in the heart of summer. A thick mulching of the foot will help to maintain it.
How to propagate lilac?
The easiest way to propagate suckering species is to take the shoots in autumn, by detaching them from the mother plant with a spade and a pair of secateurs. You can then replant them in another part of the garden immediately and water them regularly if it does not rain enough to ensure that they take root.
Cutting is easy to do. Heel cuttings or T-cuttings are the most suitable techniques for lilacs. This type of cutting is done in summer.
Take an end of a semi-lignified secondary stem carried by a healthy branch of which you will keep a small part (bark for the heel cutting, section of two centimeters for the cutting in 'T'.
Place the cutting in a bucket containing a mixture of potting soil or sand, or even a commercial 'Special seedlings and cuttings' substrate after having left only the two leaves at the top. Water and place the cutting in the shade in a place sheltered from the wind.
As soon as the first signs of recovery appear, repot in a larger pot and in a richer substrate. Keep it until the fall of the following year, when it will be time to plant your lilac in the garden!
How to plant lilac in a pot?
Potting lilacs is best done after they have bloomed in late spring.
- Choose a container or a pot of at least 40 cm in all directions with a hole in the bottom.
- Provide a layer of draining material at the bottom of the pot (pozzolan, gravel, clay balls, etc.) to ensure good drainage, as the lilac hates having its roots constantly soggy.
- Make up a mixture of potting soil, garden soil (if it is calcareous, it is even better), river sand and compost to install your shrub.
- Leave the neck of the plant 3 cm below the top of the pot.
- Pack well around the base of the plant.
- Water and adjust the height of the substrate if necessary.
How to plant a lilac in the ground?
Choose a sunny spot to plant your lilac.
- Moisten the root ball in a basin of water at room temperature after removing it from its container.
- Dig a hole twice the size of the root ball in all directions.
- Add well-decomposed compost and organic fertilizer pellets to the soil, and add a little fireplace ash if you have it. If the soil is very clayey, mix in a few shovelfuls of river sand.
- Pour this mixture into the bottom of the hole and adjust the height of the soil so that the neck of the plant is just below the soil surface.
- Backfill, keeping the shrub upright.
- Pack well around the base.
- Water copiously.
- Form a basin to retain water at the foot of the lilac.
How to prune a lilac?
Future flowering will take place on the previous year's shoots, so pruning should be done just after the spring flowering and in a delicate manner!
In addition to the pruning of wilted flowers (Cf. 'Should we cut the wilted flowers of the lilac?'), a pruning of the aerial parts can be considered but only on the subjects already well established (3 or 4 years).
The purpose of this pruning will be to clear the center of the shrub by cutting off dead or crossing branches in order to let in light and to favor natural ventilation.
If an old lilac becomes less floriferous and bald at the base, it will be possible to perform a drastic pruning of all the aerial parts. Cut the dead and oldest branches short. Cut back the others to 30 cm from the ground. This pruning should only be done in winter during the resting period, well before bud break (opening of the buds). Obviously, flowering will be compromised in the spring, but the old lilac will find a new youth.
Some species and varieties have a tendency to spread by suckers. You can prune them as close as possible to the mother plant, but be aware that this type of pruning stimulates the appearance of suckers.
Do I have to cut off the wilted flowers of the lilac?
This is not a requirement on non-remontant varieties, but it is possible to cut off spent inflorescences for aesthetic reasons. Prune above the first large bud just below the flowering stem. Cut at a sharp bevel away from the bud so that water does not linger on it.
Prune remontant varieties (which rebloom in autumn) systematically after flowering by simply cutting off the stalk of the cluster, this will stimulate the second flowering, as the shrub will not spend its energy on producing seeds.
Is it possible to grow a lilac in a pot?
It is quite possible to grow a lilac in a pot, so choose a low-growing variety such as Syringa meyeri 'Palibin' with pink flowers, S. julianae 'Red Pixie' with purple flowers, 'Bloomerang Pink' a hybrid with remontant pink flowers, or for those who like bluish shades Syringa persica 'Laciniata'.
In pots, it is important to be particularly careful about watering, as the substrate should never dry out more than 3 cm on the surface. Be also careful with a too hot exposure in the southern regions, prefer to place the pot in a shady area during the hottest hours of the day in summer.
Remember to feed the lilac with a liquid organic fertilizer (following the manufacturer's advice) or a mixture of ground horn and dried blood every 3 months from March to September.
Is the Indian lilac in the same genus as the common lilac?
No, the Indian lilac (Lagerstroemia indica) is part of the genus Lagerstroemia and of the Lythraceae family. As its Latin name does not indicate, it is native to China and not to India as one might think.
It is a tree which can reach 3 meters in height for as much of spread. It blooms in summer and is not hardy unlike the classic lilac.
Is the lilac hardy?
Yes, all species of lilac are hardy up to -15°C or more in well-drained soil, so it can be introduced in most gardens.
Attention: the Indian lilac (Lagerstroemia) which is not part of the genus Syringa (Cf. 'Is the Indian lilac part of the same genus as the common lilac? ') is not hardy, it will only be planted in the mildest regions.
When is the best time to plant lilac?
The beginning of autumn is the best time to plant the lilac, however winter and early spring are also other opportunities for planting.
Be careful, if you plant lilac in the spring, to wait until the end of the flowering period and be particularly vigilant about watering throughout the summer.
What are the most interesting species and varieties of lilac?
Among the numerous species and cultivars, here is a small selection which is not exhaustive:
- Syringa Vulgaris otherwise known as 'French lilac' or 'common lilac' comes in multiple cultivars selected for the color of their flowers. The typical species bears panicles of lilac colored flowers very perfumed.
- Among the cultivars, 'Souvenir de Louis Spaeth', 'Prince Wolkonsky' and 'Charles Joly' present clusters of purple flowers, 'Captain Baltet', 'Double bleu' and 'Firmament' decline beautiful shades of blue, 'Belle de Nancy', 'Belle de Moscou' or 'Katerine Havemeyer' resplendent in pink, while 'Madame Lemoine' remains the undisputed star of the white lilacs.
- Syringa patula 'Miss Kim' is a graceful and small (1.5 m in all directions) cultivar, ideal for small gardens. The clusters of flowers are full of small, deliciously scented pale pink flowers that maintain a very airy feel.
- Syringa meyeri 'Flowerfesta White' forms a bush of 1,25 m in all directions. It is ideal in pots or in city gardens. The fragrant, white spring flowers are repeat flowering in September/October. Note that this recent obtention is available in blue and pink.
- Syringa microphylla is an interesting species for its compact bushy habit (2 m in all directions) and its long-lasting (April to June), sometimes remontant, flowering from September to the end of October. Superba' is particularly easy to grow and is covered with pink flowers.
What are the most common diseases of lilac?
Very vigorous, lilacs are only really affected by fire blight, which manifests itself as black stained leaves and blackened shoots. Cut off all affected parts down to the sound wood, water with a decoction of garlic and spray with horsetail manure.
What are the main pests of lilac?
Otiorhynchus, cantharides and lilac moth (a caterpillar) are the most common pests. Spray fern purin every 15 days to prevent them.
