In short: lilacs need cold winters to flower well, so they thrive in cool-climate areas such as Melbourne, Canberra, Tasmania and the Adelaide Hills. Plant them in full sun and free-draining soil, prune straight after flowering, and expect blooms around October to November.
Lilacs are a beautiful plant to grow, with big bunches of colourful, scented flowers. In this guide, you’ll learn the ins and outs of growing lilacs in Australia so you can enjoy them at home.
What Is Lilac?
While the name lilac can refer to the genus of 12 species of plants in the olive family, when most people say lilac, they’re talking specifically of the common lilac, Syringa vulgaris.
The common lilac is native to the rocky hills of the Balkan Peninsula. It reached western European gardens in the 16th century through the gardens of Ottoman Constantinople, which is why it was once thought to come from further east.
Eventually, it spread well beyond the Balkans and can now be seen growing across Europe, North America and the cooler parts of Australia, due to its popularity.
It was named in the 18th century by famed Swedish botanist and taxonomist Carl Linnaeus. The genus name Syringa is derived from the Greek word for pipe or tube syrinx (think syringe). The species name vulgaris comes from the Latin meaning common (think of the modern English usage of vulgar)
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They’re often referred to as trees, which might seem correct enough since that is what they do resemble, but technically they’re considered large shrubs.
It might seem strange to see a shrub that grows 6-7 metres in height since shrubs are usually considered to grow low to the ground, but botanists do consider it to be a shrub rather than a tree.
Lilac bushes are considered quite fast growing as well, with typical growth rates being about 30 cm a year.
While their root systems tend to not grow deep, they do like to spread out from the bush quite a lot, so you need to be careful where you plant your bush. Some people have found that lilac roots tend to invade nearby septic tanks for example.
Lilacs are also known for their scents. While common lilacs that we are describing here are said to have an intense, almost spicy scent, other varieties have completely different scents. Love for them isn’t universal, with some people finding the scents of some species almost offensive.
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Lilac Varieties
In addition to the common lilac, there are several other species that people often grow.
One of the more popular species is Syringa meyeri, or the Korean Dwarf lilac. Rather than growing several metres tall, they grow to just over one metre, making them perfect for turning into hedges.
Another popular species is the Syringa × persica, or Persian lilac. This is a hybrid plant and while it’s larger than the Korean dwarf, it’s still quite a lot smaller than the common lilac, making it very suitable for modern gardens.
One downside to the common lilac is that they only bloom once a year. So if you’re a fan of lilacs and want to see them bloom more often, you might want to check out a reblooming variety such as the Bloomerang lilac, which flowers in spring and again in late summer.
Where Lilacs Grow in Australia
Lilacs need a cold winter to set their flower buds, so where you live matters more than almost anything else you do. They flower best in cool-climate areas with frosty winters: Melbourne and much of Victoria, Canberra, Tasmania, the Adelaide Hills, the Blue Mountains, and the NSW Southern Highlands and New England.
In humid, mild-winter cities such as Sydney and Brisbane, common lilacs often grow but flower poorly or not at all. If you live in a warmer area, a reblooming variety or the Persian lilac is a better bet, or enjoy cut lilac in a vase instead. Not sure what suits your climate? Our guide to planting for winter can help.
Planting and Care
Growing Lilacs from Seed
Can you grow lilacs from seeds? Yes, you certainly can. While the process itself is not too complicated, the biggest downside is that it can take several years to have trees that bloom. So this following method is really only for people who consider themselves hardcore green thumbs.
The first step is to soak the seeds in water for at least 12 hours to soften them and prepare them for the next stage.
Next, place the seeds in a bag along with some perlite and then refrigerate the seeds for a couple of months. This is to imitate the conditions during Winter so that the seeds are ready to sprout come “Spring”.
Now that “Winter” has come and gone, it’s time to plant the seeds in containers. Fill your container with seed-starting mix, plant your seed and then place the container somewhere where the temperature will be constant and not extreme.
After a month or so you should begin to see some signs of growth and once the roots begin to outgrow the container it’s time to transfer the seedlings into a bigger container. Once they grow large enough to plant (at least 10 cm tall) then you can plant them in your garden.
This is quite a laborious and time-consuming process, so if you’re just interested in having lilacs in your garden then there are quicker ways to go about it.
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How to Plant Lilacs
If you’re not patient enough to grow lilacs from seeds, then growing them from a small plant makes a lot more sense.
The best time to plant lilacs is in either Spring or Autumn.
To plant them, dig a hole in your garden slightly deeper than the container that your lilac came in. Spread the roots out around the plant and then fill the hole with topsoil, watering as you go to keep the root system moist.
How far apart to plant them depends on the variety of the plant. The smaller dwarf lilacs can be planted about 1-2 metres apart, while the larger varieties should be planted about 4-5 metres apart.
A good rule of thumb is to take the expected height of the tree and plant them that far away from each other.
In terms of soil, you’ll need to make sure that your soil is well drained and contains plenty of nutrients. They typically don’t do well in clay soil, so you’ll need to do a bit of work if your backyard is full of clay.
Lilacs do best in slightly acidic to slightly alkaline soil. Used coffee grounds can be part of a compost mix, but don’t rely on them alone. As covered above, climate matters most: they need cold winters to flower well.
Be sure to plant them somewhere that gets plenty of sun; six hours a day is preferable. Lilacs will grow in spots with less sun but they won’t bloom as well.
Speaking of blooms, if you’ve done everything else right then you can expect to see plenty of flowers in mid-spring, around October to November in most cool-climate areas. Each plant flowers for about two to three weeks.
Can You Grow Lilacs in Containers?
Because of their sheer size and root systems that love their freedom, they can be hard to grow in containers or indoors. It’s possible to do so if your container is large enough and the variety is small enough, but generally, lilacs are considered too difficult to constrain in a container.
Caring for Lilacs
Lilacs are pretty hardy plants, but there are a few things you can do to keep them in the best shape possible so they bloom as well as possible.
To start with, each Spring add a thin layer of compost and mulch to help keep the root system moist. This also has the added benefit of keeping the ground free from weeds.
In Summer, if you live in an area that doesn’t get much rainfall then you’ll want to make sure that you water your lilacs regularly.
In Winter you can add a little bit of fertiliser if you want, but over fertilising will cause the plants to stop blooming, so you need to take extra care if you’re not confident in what you’re doing.
Good news for pet owners: lilacs (Syringa vulgaris) are listed as non-toxic to cats and dogs by the ASPCA. Don’t confuse them with lilies, which can be deadly to cats. For more pet-friendly choices, see our list of pet-safe flowers for cats and dogs.
How (and When) to Prune Lilacs
Lilacs, like many flowering plants, require annual pruning to keep the blooms at a maximum. This is to funnel all the plant’s energy into the flowers rather than into creating more canes.
The best time to do this is in late Spring after the tree has bloomed.
When pruning, start by removing any dead wood and any small suckers that have appeared at the base of the tree. These suckers aren’t likely to become anything interesting and are only taking up energy that could be used by the flowers. Removing suckers is also the key to stopping a lilac from spreading.
As long as your lilac is still flowering well, you don’t need to go overboard with the level of pruning. However, if it is not flowering the way it once did, a more severe pruning may be required.
If you find yourself with lilacs in this condition, the only way to revive the tree may be to cut the tree down much more. This does mean that it will be some time before the tree blooms again, but it may be your only option at certain times.
Deadheading is the removal of dead flowers throughout the blooming season and is something that can be done to improve the yield of the plant. That said, deadheading lilac trees really only seems to be beneficial if done early in the life of the tree.
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Pests and Diseases
As with almost any type of plant, dealing with pests and diseases is another thing to concern yourself with.
Fortunately, lilacs are very hardy and it’s unusual that a tree is completely killed by a simple pest or disease.
That said, there are a couple of things to watch out for.
Firstly, slugs and snails seem to have acquired a taste for lilacs, so if you notice these guys on your trees, you’ll want to make sure that you deal with them by using appropriate treatments.
Next, powdery mildew is a disease that affects lots of plants and lilac isn’t an exception. However, where powdery mildew can slow down the growth and even be deadly to certain types of plants, it won’t kill your lilacs.
It might be ugly, but it’s not serious enough to warrant any worry.
Lilac Season Is Short
Lilacs flower for only a few weeks each spring, so enjoy them while they last. Lilacs are said to symbolise the joy of youth, and you can read more about the meaning of flowers. If you love scented climbers too, read our guide to growing jasmine.
No lilac in your garden? Send some lilac-toned colour instead with our Lilac Mini Posy or Lilac Lover Vase, with same-day delivery when you order before the daily cut-off.