14 Tips For Growing Beautiful Lilacs in Pots or Containers
If you are thinking of planting a lilac shrub in a pot or container, there are several important factors you'll need to remember for a successful planting. In this article, certified master gardener Liz Jaros walks through 14 of her top tips for growing lilacs in pots or containers this season!
Known for their tall stature, distinctive scent, and loose, arching form, lilacs are typically chosen by property owners and landscape designers who need to fill a large, sunny space with a low-maintenance, ornamental plant. I reach for them when I’m proposing a living fence or a subtle, privacy screen. Or when I need a corner shrub with a classic, cottage vibe.
Lilacs are fast-growing, beautiful, and really hard to kill. In landscape design, that’s a trifecta of good plant qualities, especially when you’re working with busy clients who aren’t going to be out there every day nursing the backyard greenery.
When recommending plant materials for a patio, balcony or rooftop garden, however, lilacs do not immediately come to mind. They have large root systems and require good drainage – two issues that can’t always be guaranteed by your average plant container.
But if you think outside the clay pot, and if you’re willing to give them a little extra attention, lilacs can perform wonderfully in a more urban or hardscape setting. Here are 14 of my top tips that you can put in place to up the odds of successfully growing lilacs in containers.
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Choose Small Varieties
With the lilac genus featuring more than 20 species and thousands of cultivars, your options might seem overwhelming. Since some types of lilacs can grow to heights of 30 feet or more and require lots of room to ramble, let’s rule out anything that exceeds 8 feet in height right away. That leaves us with plenty of dwarfs and mid-sized shrubs to consider. Here are a few that should respond well to being contained:
Dwarf Korean Lilac
Round in shape and maxing out at 4-5 feet, this dense flowering shrub produces single pink flowers in mid to late spring.
Tinkerbelle Lilac
This compact beauty can be purchased as a low mounding shrub or a lollipop-form tree. Known for its red flower buds, Tinkerbelle opens in late spring to early summer. Bright green leaves provide nice contrast. Height maxes at 6 feet.
Bloomerang Lilacs
Available in shades of pink, purple, and white, Bloomerangs also stay compact, with a 2-6 foot spread, depending on variety. The cool thing is, they will flower again if you deadhead them immediately after the first blooms have faded.
Josee Lilac
Also a rebloomer, Josee features star shaped flowers that cover the shrub almost completely in late spring. Habit is rounded and tops off at 4-6 feet.
Miss Kim Lilac
This cultivar packs a punch in early spring with large purple flower buds that open to true lavender blooms. Available in sizes ranging from mini to standard (2-8 feet tall and wide). Miss Kim’s leaves turn burgundy in fall, making these cultivars a good choice for three season interest.
Use The Biggest Pot You Can
Lilacs have very large root systems. Expect them to be as wide as the plant’s foliage or canopy, and choose a container that can accommodate rapid growth. When lilac roots are crowded, flowering will be reduced, and that defeats the purpose of featuring these beauties on the patio. And generally speaking, more soil means less supplemental watering. Another reason to go big.
Ideally, your container should be as wide as your lilac variety’s mature width. And it should be as deep as it is wide. Shoot for pots that are at least 2 feet wide and 2 feet high for the smallest lilacs, and increase dimensions as much as possible to accommodate larger lilacs.
Mind Your Materials
As long as you build in some drainage (we’ll get to that in a minute), almost anything can be used to contain your lilacs in an above ground setting. For large scale patio or rooftop gardens, this might mean a concrete planter built into the hardscape or a half wall of wooden boxes. In smaller settings, a colorful clay pot or a composite material container might be more appropriate.
Here’s a look at some of the materials often selected for container garden use, as well as some of the pros and cons for each:
Ceramic and Terra Cotta
Pots made from clay are porous, which helps with airflow, but also speeds up evaporation. They can be extremely heavy and are prone to breakage. Choose clay pots only if you intend to water diligently and will not need to move your lilacs around for any reason.
Plastic and Resin
These containers will help keep temperatures even, but be careful not to overwater since they will retain more moisture. Plastic and composite materials are ideal for small decks where weight might be an issue.
Cement
A good choice for contemporary patio design, cement pots and planters also maintain even soil temperatures, but they will be heavy and hard to move around.
Wood
Wood planters can make good lilac containers as long as you’re sure they have not been treated with chemicals. However, you can expect a lot of dirt to drain on your patio due to their porous nature. And soil will dry out quicker, so you will have to stay on top of watering.
Metal
Aluminum and copper tubs are popular choices for large-form container gardens, but they can easily overheat. On warm days, temps will be extreme in the outer few inches of dirt. These containers should only be used if they are wide enough to keep roots from burning up inside, and in settings where sunshine is filtered or partial.
Ensure Proper Drainage
Examine your pots’ drainage holes and make sure water has an adequate escape route. Standing water is one of the biggest causes of poor lilac health and diminished flower production.
If you’re working with recycled containers, make sure existing holes are clear and are between ¼ inch and ½ inch in diameter. Aim to cover about 20% of your container’s bottom surface with drainage holes. Using this as a rough guide, add more holes using the appropriate sized drill bit (or a hammer and a screwdriver) to achieve this ratio.
Rocks and broken pot pieces are not recommended for pot bottoms, as they are more likely to clog and hinder drainage than are clear, open holes.
Use The Right Soil
In a typical container garden, straight potting soil is the norm. It’s light, well-drained, and nutritionally balanced. And for a seasonal annual pot or herb garden, a soilless mix will do just fine.
A heavy shrub needs a little more stability, however, so I usually mix a little garden soil and/or compost into the potting mix to create a foundation that’s slightly sticky and dense. Shoot for a container mixture that combines roughly 10 percent compost to 50 percent potting mix to 40 percent garden soil and make sure it’s thoroughly combined before planting.
Since lilacs prefer neutral to slightly alkaline soil, strive for a pH balance of 6.5 to 7.0. If possible, do a soil test to ensure the mix in your container is lilac-friendly.
Lime and bone meal can be used to bring the acidity down if called for. Adding peat moss or sulfur to the mix will increase acidity, but should only be done if pH levels are extremely high.
Plant High Inside The Pot
If possible, start with a container grown lilac since its root system will already be limited. If roots appear dense and compact when your plant is removed from its growing container, loosen them with a garden tool or score them vertically with a blade in three or four locations.
Once the soil in your container is combined thoroughly, remove enough of it to accommodate your lilac’s root ball so that the crown will sit slightly below the rim of your container. Remember that a heavy root base will likely sink a bit after it settles.
Backfill around the rootball to a level that’s just below the crown. You want to make sure your lilac’s stems protrude from the peak of the mounded dirt, not from a concave center. A sunken crown will make your lilac more prone to rot and disease. You want water to drain down and to the sides.
Place Your Container in The Sun
Lilacs require at least 6 hours of sun and, with many cultivars that can thrive in very sunny climates. They will benefit from a location that is hot in the afternoon. While they will survive in a slightly shady spot, they will not flower well or grow as quickly. They will also be more vulnerable to shade-related conditions such as powdery mildew.
Water Diligently
The size of your pot will determine how often your potted lilac needs to be watered. A larger volume of soil will hold water longer, and you might be able to go a few days between watering. But a smaller ratio of roots to dirt means you should check them every day, or at least every other day.
Watering should be concentrated at your lilac’s roots and not its leaves, as they are prone to fungal conditions. Use a watering can or shower setting on your hose nozzle to soak but not drench the dirt surrounding the plant.
Continue watering into fall, but stop when lilac loses its leaves and enters dormancy. Begin watering again next season when soil has thawed in early spring.
Add a Layer of Mulch
To keep your potted lilac from drying out between waterings, add a layer of organic mulch around its base. Wood chips, pine bark, sawdust, hay, leaves, or a layer of compost all work well in pots.
Be careful not to pile any materials up to around your lilac’s trunk or stems, keeping a 6-inch radius completely mulch-free. This will discourage issues with rot and pests.
Fertilize for Blooms, Not Leaves
Lilacs are strong feeders and do not typically need more than an early spring shot of fertilizer. This also holds true of lilacs grown in containers. Look for granules, spikes, or a slow release formula that will deliver nutrients gradually each time you water.
A fertilizer ratio of 5-10-10 is ideal for potted lilacs, since you’ll want less nitrogen (which encourages vegetative growth) and more phosphorus and potassium (which encourage blooms). Feed lilacs annually in early spring. Repeat bloomers can get another dose later in the season. Follow your product instructions for quantities and application.
Deadhead After Flowering
Since many of the smaller lilacs well suited to being grown in a container are repeat bloomers, you should remove faded flowers in late spring to early summer to encourage another wave.
To deadhead your lilac, prune off spent blooms with a sharp cut just above the first set of leaves you encounter as you slide your fingers down their stems. This will encourage your lilac’s roots to send up new buds for a second bloom in mid-summer. Some cultivars will even send up a third bloom in late summer.
If you don’t deadhead regularly, this can impact the blooming frequency of your lilacs. So, it’s important to stay up on this routine maintenance task in order to keep the beautiful blooms you’ve come to love and expect.
Prune Annually
Like earth-grown lilacs, potted lilacs will benefit from an annual pruning and clean up. This should be done immediately after they’re done blooming for the season, as lilacs set buds for next year’s bloom shortly after this year’s cycle is complete.
Take the following steps to perform this routine maintenance on your potted lilacs:
Container Lilac Pruning Steps
- Evaluate your lilac’s size and determine if it needs to be scaled back.
- If needed, egin by taking off roughly ⅓ of your lilac’s branches with a lopper.
- Choose branches that are crossing, oddly shaped, or low hanging.
- ALWAYS make these first cuts at the plant base.
- Remove all suckers that have erupted in your pot.
- Dig down and cut suckers as close to the root base as possible.
- Remove all wood that appears gray, hollow, or dead.
- Reduce height by clipping tall canes down to roughly eye level.
- Look for a spot just above a node or set of leaves and make cuts there.
- Do not cut all canes at the same height.
- Aim for a rounded form that features longer canes in the shrub’s center.
- If lilacs are newly established or size is not an issue, perform the deadwood, crossing branch, and sucker prunes only and remove all spent blooms at a leaf set just below their stems.
Monitor For Stress
While lilacs are pretty hardy and resistant to disease, they do have some vulnerabilities and should be monitored regularly for signs of stress. Every time you water, be on the lookout for the following possible issues:
Powdery Mildew
By far the most common lilac affliction, powdery mildew presents with white, chalky leaf splotches that turn gray or black later in the season. Typically, your first signs of it will appear on lower leaves in times of high humidity and moisture.
Fortunately, powdery mildew is more of an aesthetic issue than a health issue, and your lilacs should fully recover by the following season. Cut off affected leaves, or ignore them completely until the flowering season is over, then give your lilac a good prune.
Thin your lilac’s base to encourage good air circulation. Promptly remove fallen leaves and branches, as mildew can overwinter in the soil and show up next year.
Bacterial Blight
Another moisture-related lilac disease, bacterial blight presents with brown-black leaves, distorted shoots, and sickly flowers. You might see yellow halos on your leaves or blackening flower buds if you catch it early enough.
Caused by bacteria that is always present on lilac leaves but flourishes when they’re wet, blight makes lilacs more prone to damage from the cold. Again, proper watering and aggressive pruning is key to management.
Lilac borer
This is the most common lilac aggressor and is typically found on older branches first. Adult borers are wasp-like moths with clear wings and red heads, while larvae are white-pink caterpillars with red-brown heads.
Look for cracked bark, broken branches, and/or stem holes that may exude sap or a sawdust-like excrement to indicate lilac borer infestation.
If borers are caught early, they can be effectively managed by pruning off limbs that are being attacked, so careful monitoring is key to addressing this pest. Just know that recovering lilacs may need extra watering and attention for a while.
Leafminer
Most of this pest’s damage is done by its larvae, which are small, white, and less than ¼ inch long. Yellow, squiggly lines (or mines) on your lilac’s leaves will show you where they have been boring through the tissue.
Later in the season, a rolled leaf may indicate that caterpillars are pupating. If leafminers or borers are suspected, prune off affected leaves immediately and keep your eyes peeled for others.
Scales
These small, shelled insects are about 1/16th inch long and look like tiny gray or brown warts. They typically suck sap from a lilac’s stem, which may weaken them and make them prone to breakage. Not usually a major threat if caught early, scales can be effectively managed with spot pruning and horticultural oils.
Protect Your Lilacs in Winter
While they do require some protection from extreme conditions, lilacs are cold weather plants that require a period of true dormancy if they are to flower predictably. For this reason, they should never be brought inside for the winter.
Instead, try to shield your potted lilac from high winds by moving it near your home’s foundation, or clustering it with a group of other large pots. When that’s not possible, consider piling up some evergreen branches or mulch around the base of your pot. This will protect the root systems from damaging freeze/thaw cycles.
Final Thoughts
Although lilacs are not often the first plant that comes to mind when planning a container garden, they can do just fine on patios, decks, and rooftop gardens if you’re committed to the task. The most important thing to remember is that they have large root systems, need plenty of sunshine, and require regular watering.
If you choose a small variety, use a large pot, and give them plenty of love, your container grown lilacs will give your hardscape a pastel bouquet of sweet-smelling joy year after year.
