Lilac was long considered an old-fashioned farm garden plant. However, thanks to attractive new varieties, this fragrant flowering shrub is now a firmly established presence in our gardens today. Here are tips for planting and care.
Lilac (Syringa), with its fragrant flowers, is synonymous with spring for many and today decorates countless gardens - at least in the form of the Common Lilac. From a botanical perspective, the shrub belongs to the family of olive tree plants (Oleaceae). The genus includes almost 30 species and, nowadays, countless varieties. The natural range of lilac reaches from south-eastern Europe to east Asia. Lilac should not be confused with the Butterfly bush – this comes from a different plant genus which, from a botanical perspective, is only very distantly related to the Lilac.
In the past years, the Lilac was often avoided by garden designers, as its farm garden charm didn’t work in modern garden designs. Further, gardeners had to live with the standard assortment for decades, which largely still originated from the Lemoine breed (you can read more about this under ‘Important Species and Varieties’). The Common Lilac (Syringa vulgaris), however, is one of the oldest European garden shrubs. When it - and its countless hybrids, known as the Common Lilacs – open their long panicles at the start of May (at the latest) and exude their inimitable fragrance, there is hardly anything more beautiful in the garden. Due to many breeds, the choice of robust, easy-care and attractive lilacs for the garden has increased dramatically. Recommended Lilac varieties (and their species) include the Chinese Lilac (Syringa x chinensis), or Rouen Lilac, the Meyer Lilac (Syringa meyeri), the Dwarf shrub Syringa microphylla and the Preston hybrids (Syringa x prestoniae), which are particularly frost-hardy.
Appearance and Growth
Lilac is a summer-green shrub which grows into a large shrub and occasionally a small tree. The growth heights vary greatly depending on the species: While the Syringa meyeri only grows 3 to 5 feet tall, the common lilac can reach a full 23 feet. The leaves are opposite each other, stalked and generally simple. However, there are also species and varieties with lobed or pinnate leaves. They can be oval or round to ovate or cordate. The habitus of the Lilac is extremely upright and compact. The flower buds generally form in pairs at the end of the branches which were formed previous year and, depending on the region, open from the end of April until mid May. This is when the white, yellow, pink to violet colored flowers exude their typical fragrance. After flowering, around the start of June, Lilac forms fruit capsules which contain the seeds.
Location and Soil
All Lilac species are sun worshippers and can also bear dry heat. They do also grow in shady places, but then they do not form a dense crown and have significantly fewer flowers. Common Lilac is also highly wind-resistant, which is why it is often planted as a wind-shelter hedge. Soil requirements vary: Common Lilac grows best in nutrient-rich, drier loamy, calciferous soils, whereas the Preston Lilac prefers non-calciferous and somewhat moister soils. All in all, the Lilac is extremely tolerant and does well even in less favorable soils. However, it does not cope with waterlogging and compacted soil.
The best time to plant Lilac is in the fall. The planting hole should be around twice the circumference of the root ball. For a better nutrient supply, mix the dug up soil with some compost before you use it to refill the hole. Smaller Lilac species such as the Dwarf lilac are also commercially available as standards and can even be cultivated in containers. Make sure you give the plant sufficient space and avoid waterlogging.
Lilac is extremely easy-care, as grown plants can even manage in dry summers without watering. In sandy soils, the flowering shrub should be provided with additional nutrients in the form of or long-term fertilizer. If you apply a thin layer of mature compost to the tree base every spring, you will enrich the soil with humus and improve its ability to store water and nutrients.
Lilac already form flower buds in the previous year. To prevent unnecessary reduction of the blossoms, limited pruning should only be carried out at the end of May, after flowering. When pruning Lilac try to deadhead all panicles above two well-formed side buds. This prevents seed from forming and stimulates the shrub to form new flower buds which will then open next season. You can bring aged shrubs back into shape with heavy trimming of the main branch to 16 to 24 inches long (rejuvenation cut). If you want to grow the lilac with one trunk as a standard tree, cut off all side branches and bothersome side shoots if possible when the plant is still young.
Lilac are excellent as solitary plants, but they can also be combined with other flowering shrubs. Ideal plants which flower around the same time include, Beauty bush (Kolkwitzia), Mock orange (Philadelphus) and Weigela (Weigela).
Lilac hedges also serve a purpose and are a real eye-catcher during the flowering period in May. Small-growing species such as the Dwarf Meyer lilac (Syringa meyeri ‘Palibin’) which grow to just 4 feet, are great for keeping as winter-hardy container plants on the terrace. As the shrubs form a very thick root network and often also off-shoots, under-planting in the garden isn’t easy: Choose different flowering bulbs or shrubs which are extremely robust and also tolerate dryness, such as Turkish sage (Phlomis russeliana), Snowdrop anemone (Anemone sylvestris) or Big root geranium (Geranium macrorrhizum).
Tip: Lilac looks great in a vase, although it dies quickly in these. Its scent can fill entire rooms. A pleasant side-effect: If you regularly cut a few bouquets during the flowering period, you automatically prevent the crown from aging and balding.
Important Species and Varieties
An Austrian envoy brought the Lilac from Turkey to the Vienna court in 1565. From here, the flowering shrub proceeded to move into gardens in Central Europe. A diverse range of species developed from intensive breeding in particular in the Lemoine nursery in Nancy/France at the end of the 19th century. The previously mentioned Common Lilac helped the shrub to finally make a breakthrough as a garden plant. In English, the Common Lilac and its cultivated forms are still known under the name ‘French lilac’.
But as previously mentioned, where the diversity of varieties is concerned, a lot of progress has been made over the past years: The current varieties of Common Lilac have significantly improved characteristics. They are more robust and generally somewhat more compact than the older varieties. Their flowers are often two-tone as the bud bracts are often darker than the petals. All Common Lilac varieties can grow 13 to 20 feet tall and can also be trained as small, single-trunk flowering standard trees. They can grow to be very old and occasionally form offshoots.
The Preston hybrids (Syringa x prestoniae) are playing an ever greater role. They are commercially available as Preston lilacs. This concerns varieties which resulted from crosses around 1920 between the Nodding Lilac (Syringa reflexa) and the Late Lilac (Syringa villosa). They are extremely frost-hardy, have particularly long, delicate panicles and flower somewhat later than the varieties of Common Lilac. Preston hybrids are the first choice for smaller gardens as they hardly grow taller than 10 feet. A cultivar trial in the Netherlands assessed the varieties ‘Minuet’ (pale violet) and ‘Redwine’ (purple-red) as ‘Excellent’.
Common Lilac was previously mostly propagated through grafting, i.e. the plant roots originate from the Common Lilac. However, this tends towards offshoot formation and promotes lots of little, wild Lilac saplings. Today, more and more Common lilac are grown ‘self-rooted’ from cuttings or through meristem propagation in a laboratory: On one hand, self-rooted common varieties form fewer offshoots and on the other, they have varietal purity. Therefore, you should buy self-rooted varieties of Common Lilac wherever possible.
If you want to propagate Lilac yourself, this is easiest by planting root offshoots in the spring of fall. But take care with Common Lilac varieties: These are often grafted to wild seedling species, which means that their offspring will be a ‘wild plant’. The Chinese lilac, Nodding lilac (Syringa reflexa) and Hungarian lilac (Syringa josikaea) can be propagated using hardwood cuttings. Dwarf Lilacs can only be propagated with cuttings.
Sowing seeds is also possible with wild species. For this, simply harvest the dry infructescenses in October and shake out the seeds, then place these into propagation boxes with potting compost. These can then remain outside until January, but they should not be allowed to fully dry out during this time. Then, they can be covered in an unheated greenhouse, where the seeds will start to germinate. The seedlings can be planted in individual pots in the spring, in the fall they can be put in the garden.
Diseases and Pests
A typical pest which can occur on Lilac is the Lilac lifeminer or Privet Leafminer. An infestation can be recognized by brown leaves in May. In general, a sufficient treatment is to pluck off the Larvae by hand when they are spotted. Aphids and Powdery Mildew can also occur, but do not cause a great deal of damage.
Frequently Asked Questions
What is Lilac?
Lilac is a genus encompassing around 30 species from the olive family. The shrubs are particularly popular in farm gardens.
How tall do Lilac grow?
The growth height can vary greatly depending on the species, from 3 to 23 feet, and everything in between.
When can Lilac be planted?
Lilac is best planted in the fall.
When does Lilac flower?
Lilac generally flowers from the end of April to the start of June.
When can I prune Lilac?
Lilac should be pruned at the earliest at the end of May, after flowering. More extensive trimming should be left until the fall.
How should Lilac be pruned?
The panicles should be deadheaded if possible above two well-formed side buds. Cut back the main branch to 16 to 24 inches long for a rejuvenation cut. If you would like to grow Lilac as a single-trunk, small tree, cut the side branches and bothersome side shoots off when the tree is still young.
How can Lilac last longer in a vase?
To make Lilac longer lasting in a vase, the leaves should first be removed and the stalks cut diagonally. The stalks of very woody shoots can also be split with a sharp knife. The water should also be changed regularly. When the water is changed the stalks can be re-cut.