How to Grow Lilacs for Spring Color
The very first house that I ever owned was about 100 years old and had an old lilac bush planted outside the back door. I loved the fragrance of the flowers every year in May when it bloomed. The circumstances of my life changed, and I had to sell that house and buy a smaller one. The first thing I did after I moved was to plant a lilac bush outside of the back door of my new home!
What Are Lilacs?
Although we refer to them as bushes, lilacs are multi-stemmed deciduous trees that grow from 8 to 30 feet tall depending on the species. There are a total of 12 species. Lilacs are related to olives trees and like olive trees, they are native to an area stretching from southeastern Europe to eastern Asia. They were brought to the US by European colonists. They are hardy in zones 3 through 7.
The most common cultivar grown by homeowners is what is known as French lilacs. They are called French because they were developed by a French breeder, Victor Lemoine. The flowers are double meaning they have more petals than the original species making them more attractive to home gardeners.
Lilacs are known by their characteristic heart shaped leaves. Their flowers grow in pannicles which are many flowers growing on one stem. Lilac flowers individually are quite small. They come in different colors including lavender, dark purple, burgundy, yellow and white. The flowers appear for only 2 weeks, usually in late May although a few cultivars bloom at different times during May. Some home gardeners plant different cultivars in an effort to extend the blooming season for as long as 6 weeks.
How to Grow Lilacs
If you are planning a lilac hedge or want to attempt to extend the blooming season by planting different cultivars, be sure to plant your bushes at least 10 to 15 feet apart. Lilacs are large plants and need lots of space to grow.
Lilacs need to be grown in rich, well-drained soil. Working some compost into the soil will keep your lilacs happy. But don’t add fertilizer. Compost is all that they need. They also need enough moisture, at least 1 inch per week. A thick layer of mulch will help retain moisture as well as keep down weeds.
Lilacs need full sun. If they are grown in partial shade, they will not bloom well. If they are growing in full shade, they will not bloom at all. It is important to make sure that your shrub is getting a minimum of 6 to 8 hours of sunlight each day. Another cause of poor blooming is that your lilac needs pruning.
How to Prune Lilacs
The most important thing to remember when pruning your lilac is that it blooms on old wood. This means that the flower buds were formed last year so if you prune in the fall or the spring, you will be cutting off branches that have flowers buds so your shrub will not bloom well or not at all. The best time to prune is right after your bush has finished blooming. It has not yet had time to form new buds for next year so you won’t have to worry about accidentally cutting off next year’s flowers.
You should remove any dead or diseased branches or stems and any branches that are crossing each other. Lilacs are prone to powdery mildew which can occur due to poor air circulation. Good practice is to thin out the stems to encourage good air circulation.
Once established, lilacs can live for hundreds of years. The downside is that the older stems do not bloom as well. You can rejuvenate an old lilac using what I call The Three Year Plan. The first year, remove ⅓ of the oldest, thickest stems cutting them down right to the ground. The following year, remove half of the remaining old thick stems. The third year, remove all of the old thick stems that are left. You will be left with vigorous, new growth that will produce more blossoms.
How to Propagate Lilacs
Lilacs are easy to propagate. The easiest way to grow a new lilac bush is if another gardener gives you an offset or sucker from their bush. Suckers are stems that grow from the existing root system of a lilac bush. You will receive a stem and part of the root system to which it is attached. Simply dig a hole in a sunny location and plant your sucker. Keep it well watered as it establishes itself in its new home. Don’t expect flowers the following spring. New lilac bushes take 4 to 5 years to mature enough to blossom.
The second easiest method is by cuttings. In the spring when the new growth has reached a length of 4 to 6 inches, cut off as many stems as you need. Dip the cut ends in rooting hormone and then stick them into the ground in a sunny spot where you want them to grow. Keep them well-watered. Roots should form in 3 to 6 weeks. Alternatively, you can instead plant your cuttings in containers and then after they form roots, transplant them to their new permanent home. Roots have formed if there is resistance when you gently tug on the cutting. Like suckers, you will have to wait 4 to 5 years for flowers.
You can also grow lilacs from seed but don’t expect the resulting plants to look anything like the bush from which you collected them. Most of the lilacs you purchase are hybrids, crosses between different cultivars. They do not come “true” from seed. The seeds may produce plants that look like either of the cultivars from which your shrub was bred or something completely different. It’s a genetic lottery!
Lilac seeds are very hard and need to be soaked for 24 hours before planting. Plant them ¼ inch deep in containers and then cold stratify them by placing covering the containers and storing them in your refrigerator for two months to simulate winter. Don’t let them dry out. Gently mist the containers to keep the soil moist.
After the two months is up, remove the containers from the refrigerator and place them on a heat mat set to 70⁰F to simulate spring. Keep the soil moist. Germination should occur in a month. Keep the containers on the heat mat for an additional two weeks after germination. After that, you can remove the heat mat. You can plant your seedlings outdoors after your last frost, spacing them 10 to 15 feet apart. Your new plants should start blooming in 4 to 5 years.
I learned in a college class on archeology that here in the US lilacs are a good indicator of homestead sites because they are not native here. If you see an old lilac growing in the middle of nowhere, someone planted it there. Look around the area surrounding the lilac and you will find the foundations of an old house. The house may be gone but the long-lived lilac is still growing and blooming where it was planted so many years ago.
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© 2018 Caren White