13 Perennials You Should Never Plant Next to Each Other
Strategic plant placement prevents crowding and ensures robust perennial growth.
Perennial plants form the backbone of many gardens, returning year after year with reliable beauty or harvests. But not all perennials get along well together—some combinations can lead to stunted growth, pest issues, or one plant overtaking its neighbors.Understanding which perennials should be kept apart is key to fostering a thriving, attractive, and manageable garden landscape.
Understanding Perennial Plant Compatibility
While perennials inspire gardeners with their longevity and seasonal return, plant compatibility is essential. Some perennials are aggressive spreaders, others emit toxins through their roots, and some simply need different amounts of water or sunlight. Planting incompatible species together may result in poor growth, greater disease vulnerability, or even the loss of less vigorous plants.
This guide examines thirteen perennial plants that are best kept away from one another, offering practical advice for garden planning and maintenance.
Contents
- Why Keep Certain Perennials Apart?
- 13 Problematic Perennial Pairings
- Principles for Planning a Harmonious Perennial Bed
- Frequently Asked Questions
Why Keep Certain Perennials Apart?
Not all perennials are good neighbors. There are several key reasons to separate specific plants:
- Allelopathy: Some plants release chemicals that inhibit the growth of others, such as black walnut or tansy.
- Resource Competition: Vigorous perennials may outcompete less aggressive types for water, nutrients, or sunlight.
- Pest and Disease Spread: Placing closely related plants together can make them more susceptible to shared pests and diseases.
- Differing Environmental Needs: Plants with contrasting moisture or sunlight needs are less likely to thrive when grouped together.
- Invasive Growth: Fast-spreading perennials can choke out or smother their neighbors.
13 Problematic Perennial Pairings
Below is a comprehensive guide to thirteen perennials that should never be planted directly next to certain other species, with explanations for their incompatibility and safer alternatives.
1. Tansy and Most Other Plants
Tansy (Tanacetum vulgare) is an assertive grower, known for suppressing or overwhelming almost any companion. Its allelopathic tendencies release chemicals that inhibit growth in nearby plants. Tansy also spreads vigorously, crowding out neighbors.
Recommendation: Only plant tansy in containers or isolated beds, and deadhead flowers to prevent rampant seeding.
2. Mint and Other Low-Growing Herbs
Mint (Mentha spp.) aggressively spreads via runners. Mixing it with less vigorous herbs like thyme or oregano usually results in mint overrunning the bed.
Recommendation: Grow mint in pots or use root barriers to prevent its spread.
3. Bee Balm and Lavender
Bee balm (Monarda didyma) prefers moist soil and will quickly overtake less vigorous neighbors. Lavender (Lavandula spp.) dislikes extra moisture and can develop root rot.
Recommendation: Pair bee balm with other moisture-loving perennials and lavender with drought-tolerant ones.
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4. Asparagus and Garlic/Onions
Asparagus (Asparagus officinalis) develops deep roots and will suffer competition from garlic or onions planted nearby. These alliums can also introduce soil-borne diseases harmful to asparagus.
5. Bearded Iris and Ferns
Bearded iris (Iris germanica) thrives in well-drained soil and dislikes wet environments. Ferns require consistently moist, shaded conditions.
Recommendation: Keep irises in sunny, well-drained locations, while grouping ferns in shaded, damp zones.
6. Daylilies and Roses
Daylilies (Hemerocallis spp.) are robust, forming dense root systems that compete for water and nutrients, impeding roses, which are heavy feeders themselves.
7. Comfrey and Shallow-rooted Plants
Comfrey (Symphytum officinale) is valued for dynamic nutrient accumulation but develops deep roots and large leaves that create heavy shade, stunting shallow-rooted or small plants placed close by.
8. Chives and Beans/Peas
Chives (Allium schoenoprasum) and other alliums can exude substances that inhibit the growth of legumes, such as bush or pole beans and peas.
9. Echinacea and Black-eyed Susan
Echinacea (Echinacea purpurea) and black-eyed Susan (Rudbeckia hirta) look beautiful but compete for similar nutrients and water, leading to stunted growth or one overtaking the other.
10. Artichoke and Vining Crops
Artichoke (Cynara scolymus), with its large, thistle-like structure, shades out and outcompetes nearby vining crops like pumpkins or squash.
11. Sage and Cucumber
Sage (Salvia officinalis) is known to stunt the growth of cucumbers through chemical emissions and differing soil preferences.
12. Peony and Trees/Shrubs
Peony (Paeonia spp.) needs open ground and dislikes competing with the deep, extensive root systems of trees and large shrubs, leading to poor flowering.
13. Lily-of-the-Valley and Most Low-Growing Plants
Lily-of-the-valley (Convallaria majalis), while attractive, spreads aggressively via rhizomes, smothering smaller or less vigorous perennials.
| Perennial | Problematic Neighbors | Reason | Better Companions |
|---|---|---|---|
| Tansy | Almost all | Allelopathic, highly invasive | Containers, isolated beds |
| Mint | Low-growing herbs | Spreads by runners | Other mints, pots |
| Bee Balm | Lavender | Moisture preference conflict | Moisture-lovers |
| Asparagus | Garlic, Onions | Soil-borne disease, root competition | Tomatoes, parsley |
| Bearded Iris | Ferns | Soil moisture conflict | Other dry-soil plants |
| Daylilies | Roses | Root/nutrient competition | Other daylilies |
| Comfrey | Shallow-rooted plants | Deep roots, shading | Large perennials |
| Chives | Beans, Peas | Growth inhibition of legumes | Carrots, tomatoes |
| Echinacea | Black-eyed Susan | Resource competition | Grasses, less competitive flowers |
| Artichoke | Vining crops | Shade, resource competition | Sun-loving shrubs |
| Sage | Cucumber | Allelopathy, differing needs | Lavender, rosemary |
| Peony | Trees, shrubs | Root competition | Open beds |
| Lily-of-the-Valley | Low-growing plants | Invasive rhizomes | Contained spaces |
Principles for Planning a Harmonious Perennial Bed
- Research Each Plant: Understand root systems, moisture, and light requirements before planting together.
- Group by Similar Needs: Place plants with comparable sunlight, water, and soil preferences together.
- Contain Aggressive Species: Use pots, root barriers, or isolated beds for spreaders like mint, tansy, or lily-of-the-valley.
- Stagger Heights and Growth Habits: Avoid shading out shorter plants by positioning taller species to the north (in the Northern Hemisphere).
- Rotate Plantings: In mixed beds, rotate some perennials yearly to disrupt pest and disease cycles.
- Mulch and Prune Regularly: Control spread and maintain air circulation to promote health in denser beds.
Frequently Asked Questions
Q: Can perennials be relocated if they’re already competing?
A: Yes, most perennials can be moved in early spring or fall when dormant. Carefully dig up the plant with as much root as possible, prepare a suitable new site, and water it well after transplanting.
Q: Is companion planting with perennials the same as with annuals?
A: Not always. Many annuals grow quickly and are replaced each season, while perennials are long-term residents. Their root systems and competition dynamics can be quite different, so compatibility is crucial for long-term success.
Q: Are there perennials that nearly always grow well together?
A: Yes, many perennials with similar growth habits, light, and water needs—such as ornamental grasses with coreopsis or echinacea—form mutually beneficial groupings that endure for years.
Q: What methods stop aggressive perennials from taking over?
A: Containment is key. Plant in pots sunk into the ground, use landscape edging or physical root barriers, and deadhead flowering stalks to minimize self-seeding where applicable.
Q: How do I tell if a plant is too aggressive for a mixed bed?
A: Monitor for rapid horizontal growth by roots, runners, or rhizomes, and unintentional reseeding. If you find the plant doubling in spread each year, it’s likely to become a problem neighbor.
Key Takeaways for Smart Perennial Pairings
- Keep aggressive and allelopathic perennials contained or isolated.
- Plant together those with similar environmental needs and growth rates.
- Avoid pairing plants with conflicting resource or space requirements.
- Careful planning leads to balanced, easy-care perennial beds for years of enjoyment.
References
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