After spending many years rehabilitating neglected lilac bushes and planting new ones in all sorts of garden configurations I’ve learned what works – and what spectacularly fails – when it comes to companion planting with lilacs.
These are what NOT to plant with lilacs, straight from my own garden disasters and triumphs.
Understanding Lilacs
Lilacs (Syringa) are complex characters with, like all flowers and plants, their own specific needs. These long-lived shrubs can thrive for generations but they’re surprisingly picky about their garden companions.
Most lilacs need full sun (at least 6 hours daily), well-drained soil with a neutral to slightly alkaline pH (around 7.0) and good air circulation to prevent powdery mildew.
Here’s why companion planting matters so much with lilacs: they have extensive, shallow root systems that can extend well beyond their drip line. This means they’re constantly competing for water, nutrients and space both above and below ground with whatever you plant nearby.
I learned this lesson when I enthusiastically planted a ring of hostas around my prized ‘Miss Kim’ lilac. Within two seasons, both plants were struggling – the lilac’s lower branches lost leaves, the hostas looked stunted, and neither flowered well. That’s when I started paying serious attention to what should and shouldn’t be planted near these finicky shrubs.
13 Plants You Should Never Plant with Lilacs
1. Black Walnut Trees
Black walnut trees are basically the neighborhood bullies of the plant world (I’ve written about them a lot on here!), and lilacs want nothing to do with them. These trees produce juglone, a chemical compound that’s toxic to many plants, lilacs included.
Why they don’t mix:
- Juglone in black walnut roots, leaves, and nuts is toxic to lilacs
- Effects can persist in soil even after tree removal
- Damage develops slowly but is nearly impossible to reverse
2. Other Large Shrubs and Trees
In the past Ive seen a weeping willow shade out some gorgeous lilacs in just a few years, and since then I’ve become extra cautious about planting any large woody plants too close to lilacs. Trees and large shrubs like dogwoods, maples or viburnums might seem fine at first, but as they mature, they create too much competition.
Why they don’t mix:
- Compete aggressively for water and nutrients
- Create shade that reduces lilac flowering
- Limit air circulation, increasing disease risk
- Root systems fight for the same space
3. Clematis
This one surprised me. I once thought the purple flowers of clematis vines would look stunning climbing through my white lilacs. Big mistake.
While clematis looks gorgeous temporarily, it’s actually a terrible companion. The vine tends to use the lilac as a living trellis, eventually weighing down branches and potentially damaging the structure of your shrub.
Why they don’t mix:
- Clematis can strangle lilac branches
- Both plants compete for the same nutrients
- Clematis may harbor diseases that affect lilacs
- Makes pruning nearly impossible without damaging one or both plants
4. Hostas
I mentioned my hosta disaster earlier and I’ve seen the same problem in other gardens too. While hostas seem like perfect lilac companions since they thrive in partial shade (which lilac bases naturally create), their extensive root systems compete directly with lilac’s shallow roots.
Why they don’t mix:
- Compete for water and nutrients
- Hostas may attract slugs and other pests that can damage young lilac shoots
- Dense hosta foliage can trap moisture at the base of lilacs, promoting fungal problems
5. Aggressive Ground Covers
English ivy, pachysandra and vinca might seem like good options for covering the bare ground beneath lilacs, but I’ve watched these thugs strangle more than one lilac over time. My friend’s beautiful ‘Charles Joly’ lilac was nearly killed by an aggressive English ivy that climbed right up into the shrub.
Why they don’t mix:
- Steal water and nutrients from shallow lilac roots
- Can climb and smother lower branches
- Often harbor snails and slugs that damage lilacs
- Make it difficult to mulch, fertilize, or care for lilac base
6. Most Vegetables
The heavy feeding and frequent watering vegetables need is simply incompatible with established lilacs, which prefer consistent but not excessive moisture.
Why they don’t mix:
- Vegetables typically need more frequent watering than lilacs
- Veggie fertilizers often contain too much nitrogen, promoting leaf growth over flowers
- Vegetable garden activities (planting, harvesting) can damage lilac roots
- Different pest management needs create conflicts
7. Roses
This pairing looks romantic in theory but creates a maintenance nightmare. I tried planting ‘New Dawn’ roses near my ‘President Lincoln’ lilac and ended up with both plants suffering from blackspot and competing root systems. Both roses and lilacs are heavy feeders with different soil preferences.
Why they don’t mix:
- Roses prefer slightly acidic soil; lilacs prefer neutral to alkaline
- Both attract similar diseases but require different treatments
- Competing root systems struggle for dominance
- Different pruning schedules make maintenance complicated
8. Rhododendrons and Azaleas
The soil preference mismatch here is dramatic. Rhododendrons and azaleas demand acidic soil (pH 4.5-6.0), while lilacs need neutral to slightly alkaline conditions (pH 6.5-7.5).
Why they don’t mix:
- Completely opposite soil pH requirements
- Different water needs (rhodies like consistent moisture)
- Competition for nutrients
- Contradictory fertilizer needs
9. Shallow-Rooted Perennials
Daylilies, iris and similar shallow-rooted perennials might seem like they’d work well under lilacs, but they compete directly with lilac roots.
Why they don’t mix:
- Direct competition in the same soil layer
- Often require more water than is ideal for lilacs
- Can make it difficult to mulch properly around lilac base
- May need division or maintenance that disturbs lilac roots
10. Butterfly Bush (Buddleia)
Despite both being butterfly magnets, these plants make terrible neighbors. The butterfly bush’s rapid growth and similar resource needs create direct competition.
Why they don’t mix:
- Similar growth habits create competition
- Both need full sun to flower properly
- Both are heavy feeders requiring similar nutrients
- Can cross-contaminate each other with pests and diseases
11. Grass and Lawn
Turfgrass growing right up to the base of lilacs is something I see constantly in newer landscapes, and it’s a recipe for stunted growth. The shallow roots of grass compete directly with lilac roots, and mowers and string trimmers can damage the trunk bark, creating entry points for disease.
Why they don’t mix:
- Grass roots compete directly with lilac roots
- Lawn maintenance equipment damages lilac trunks and roots
- Lawn fertilizers often contain too much nitrogen
- Grass traps moisture against lilac bases
12. Other Lilacs (Too Close)
I made this mistake at my first house, planting six different lilac varieties within a 10-foot area. Turns out lilacs don’t even like other lilacs when planted too closely! While a lilac hedge with proper spacing works beautifully, cramming different varieties too close creates competition and increases disease spread.
Why they don’t mix:
- Increases spread of diseases like powdery mildew
- Creates intense root competition
- Makes proper air circulation impossible
- Complicates pruning and maintenance
13. Plants Requiring Acidic Soil
Blueberries, mountain laurel and other acid-loving plants are completely incompatible with lilacs. These plants have fundamentally different soil needs that can’t be reconciled.
Why they don’t mix:
- Contradictory soil pH requirements
- Amendments for one will harm the other
- Different fertilizer needs
- Wasted effort trying to please both
Good Companion Plants for Lilacs
After all those disasters, you might wonder what actually DOES work with lilacs. Plenty, thankfully. Through trial and error I’ve found several plants that peacefully coexist with my lilacs:
- Spring bulbs (tulips, daffodils, crocus) that bloom before lilacs leaf out fully
- Shallow-rooted annuals like sweet alyssum or pansies
- Drought-tolerant perennials like catmint, Russian sage, or sedum
- Herbs such as lavender, thyme, and oregano
- Native prairie plants that don’t mind drier conditions once established
These plants either complete their major growth before lilacs need resources, have compatible needs or stay small enough not to compete aggressively with established lilacs.
Tips for Successful Companion Planting
This is what has saved me countless headaches when planting with lilacs:
- Respect the drip line – Keep most plantings beyond the outer reach of lilac branches
- Consider mature size – That cute little perennial might spread 3 feet in all directions eventually
- Mind the mulch – A 2-3 inch layer of mulch helps suppress competitors and retains moisture
- Test your soil pH before planting companions – aim for 6.5-7.5 for lilac happiness
- Think seasonally – Early spring bloomers often work well since they’re dormant during lilac’s heavy growing season
- Watch water needs – Group plants with similar irrigation requirements
Final Thoughts
Lilacs might be particular about their companions but isn’t that true of most worthwhile relationships? With their intoxicating fragrance and long lifespans these shrubs deserve thoughtful neighbors that bring out their best qualities.
I’ve killed enough plants through bad pairings to know that researching compatibility before planting saves heartache, time and money. My worst gardening moments have come from ignoring the basic needs of plants and trying to force incompatible species to live together.
The best garden designs work with nature’s preferences rather than against them. If you’re committed to growing healthy, flowering lilacs for decades to come, give them the companions they deserve – ones that complement rather than compete.