Lilacs: Planting, Care and Pruning

On the weekend, we stopped to pick some white lilacs that were growing wild in an open country field.

The fragrance was heavenly; a mix of clover and honey, with the slightest hint of spice. Even when you crush the woody stems, lilacs in a vase never last long, but that only makes you savour them all the more.

Lilacs in my garden.

That the lilacs were blooming in an old farm field, with not a single gardener in sight to coddle them, speaks volumes to the self-reliance and hardiness of these springtime favourites. They seem to thrive on benign neglect!

The common lilac, Syringa vulgaris is easily grown in full sun in just about any well-drained soil. (The only exception might in the deep south (USDA zones 8-9) were lilacs do not cope well with the heat and humidity.)

Over and above the common mauve lilac, modern cultivars offer double flowers and a range of colors including white, cream, rose, magenta and purple. Heights range from dwarf varieties at 5-8 feet to tall shrubs that can reach as much as 30 feet.

There are a few drawbacks with lilacs that should be mentioned. These are spring stars with no second act. There isn't any showy fruit, nor is there attractive fall foliage color. Lilacs are also really prone to mildew, especially when stressed by drought.

In my garden, old-fashioned mauve lilacs and a couple of modern cultivars bloom mid-May and are pretty much done by the time the dwarf standards begin to flower. The three standards, Syringa meyeri 'Palibin' fill the garden with the most amazing perfume! Nothing in my garden, save for some oriental lilies, is as fragrant. Blooming alongside the standards is a three year old Bloomerang Lilac. The Manchurian Lilac, Syringa pubescens subsp. patula 'Miss Kim' in the front yard is the last to bloom.

My Bloomerang lilac is flowering now.

Interesting to note that the new Bloomerang series of lilacs (from Proven Winners) are repeat bloomers.

'Dark Purple' and 'Purple' have, as their names suggest, purple flowers. 'Scent and Sensibility Pink' and 'Pink Perfume' have repeating rose colored flowers. These new shrubs are dwarf in size making them a good choice for a small garden. As with common lilacs, they need full sun and good drainage.

Here are a few notes on planting, ongoing care and pruning for lilacs:

Planting:

• You can plant lilacs in both the spring and fall, although spring is best. Roots of a lilac bush spread out horizontally, so if you are planting a hedge, space them at least 5 feet apart.

• Choose a location with a least 6 hours of sun. Too much shade and you'll have small leaves and few flowers.

• Lilacs are pretty adaptable to a range of soil types, but humus-rich soil is ideal.
• Soil that will drain freely when rainfall is plentiful is also crucial.
• It's always a challenge to look at a small shrub in a nursery pot and imagine its mature size years down the line, but do your best. Check the plant label to confirm your lilac's mature height and spread.
• Dig a planting hole that is deep and wide enough to accommodate the lilac's root system. Remove the shrub from its nursery pot and insure the top of the root ball is level with the surface of the soil. Back fill and water well.

Ongoing Care:

With the exception of a regular pruning, lilacs are very easy-going.  Use of a fertilizer isn't essential, in fact a lilac that is has been given too much fertilized won't flower. Lilacs can however benefit from an application of a some compost in spring. A top dressing of mulch to help the soil under your shrub retain some moisture and will keep weeds at bay.

General Notes on Pruning:

When it comes to pruning, it is important to remember that most lilacs bloom on old wood.  That means the best time to prune a lilac is right after it finishes flowering. This gives the shrub the remainder to the growing season to develop the buds that will be next spring's flowers

The exception to this rule would be the new Bloomerang Lilacs. They bloom on new growth and should be deadheaded regularly to encourage new blooms.

Light Annual Pruning of a Common Lilac:

• Begin by removing spent blooms and any crossing or dead branches. Cut back any weak branches to a strong shoot.
• Suckers take energy away from the rest of the lilac, and on top of that, they look rather messy. Remove any small suckers growing from the main trunk and leave just a couple of healthy ones that will eventually become replacements for older stems.
• A lilac bush should look full, but not overly bushy. Opening up the centre of a lilac by trimming away a couple of the interior branches will allow more air circulation and help to prevent powdery mildew.

Pruning a Neglected or Mature Shrub:

• Again, begin by removing any the spent flowers. Then prune any crossing or dead branches. Cut back any weak branches to a strong shoot.
• To reinvigorate the shrub, prune a few of the oldest stems right to the ground. Next remove any small or weak suckers at the base of the lilac, but leave a few healthy stalks that will mature to replace the old stems you are removing.

Pruning a Dwarf Lilac:

Dwarf lilacs such as Manchurian Lilac, Syringa pubescens subsp. patula 'Miss Kim' don't require much more than deadheading any spent flowers. Mature shrubs can become leggy over time and may benefit with the removal of a few of the oldest stems every few years.

Pruning a Standard Lilac:

The best time to prune a standard lilac is after it finishes flowering. Prune away faded flowers and then stand back to look at the overall shape of your standard. A lilac standard should not be a tightly clipped ball, but you may want to make a few adjustments to help your standard lilac keep a pleasant, rounded shape.

Pruning a Bloomerang Lilac:

Bloomerang Lilacs bloom on new growth. Cut the stem back to just above the closet pair of side shoots.

Removing spent flowers and doing a light pruning after a these new cultivars flower encourages fresh growth and more blooms. 

Why isn't my lilac blooming? A few suggestions:

If a lilac doesn't get enough sun, it won't bloom well.

Lilacs don't like wet feet and will not bloom if the soil is too moist.

If the flowers on your lilac are small and sparse, it may be a sign that your shrub is overdue for a good pruning. Pruning lilacs improves their health and encourages new flower production.

Propagating lilac bush:

• Fill a small bucket with water and then look for a sucker at the base of a mature lilac's trunk.
Dig down to expose the roots of the shoot. Cut it away from the mother plant making sure to include some of the roots.
• Place the shoot in your bucket of water to prevent it from wilting while you dig the planting hole.
• Plant the lilac sucker in a suitable location and give it a good soak.
• Water the new shoot regularly until it takes hold. Expect to wait 4 to 5 years before you are rewarded with blooms.

Pests and Diseases:

During a hard winter, mice and voles can naw on the bark of a lilac at ground level. Discourage this by keeping mulch and leaf litter away from the base of your shrubs in the fall.

Lilac Borers are a common problem. An adult Lilac Borer is a wasp-like moth with brown forewings and transparent hind wings. The larvae is a white caterpillar with a brown head. Adult borers appear in late summer, mate and lay eggs. Tiny caterpillars hatch, tunnel into main stems and weaken the shrub.
Heavily infested stems should be pruned out. In lightly infested shrubs, borers may be destroyed by probing with a flexible wire.

Greyish-white patches on the foliage of a lilac is a sign of powdery mildew. The good news is that powdery mildew, while somewhat unsightly, does not pose a serious threat to a shrub's health.
Prevention is the best strategy to adopt. Shady conditions and poor air circulation encourages the development of powdery mildew.
When the summer is particularly hot and dry, I find my lilacs are stressed and more susceptible to powdery mildew. If there has been less than a inch of rain in a one week period, give your lilac a good drink.

It just wouldn't be spring without the sweet scent of lilacs!

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