Harnessing Plant Relationships for Pest Control
Companion planting is the practice of growing different plants together for mutual benefit. This ancient technique has been used by farmers and gardeners for centuries to naturally manage pests, improve pollination, enhance growth, and increase yields. This fact sheet focuses on using companion planting specifically for pest management in African garden contexts.
How Companion Planting Works
Plants interact with each other and their environment in several ways that can help reduce pest problems:
Pest Deterrence Mechanisms
- Masking: Strong-smelling plants can hide the scent of companion plants from pests
- Repelling: Some plants release compounds that actively repel specific pests
- Trapping: Certain plants attract pests away from valuable crops
- Beneficial insect attraction: Plants that attract predatory insects that feed on pests
- Physical barriers: Tall or dense plants can block pest movement
Benefits Beyond Pest Control
While this fact sheet focuses on pest management, companion planting offers additional benefits:
- Improved pollination through increased beneficial insect activity
- Enhanced plant growth through nutrient sharing and soil improvement
- More efficient use of garden space
- Increased biodiversity and ecosystem resilience
- Improved flavor in some culinary herbs and vegetables
Key Companion Plants for Pest Management
Aromatic Herbs
- Basil: Repels flies, mosquitoes, and tomato hornworms; improves flavor and growth of tomatoes
- Mint: Deters ants, aphids, cabbage moths, and rodents (best grown in containers to prevent spreading)
- Rosemary: Repels cabbage moths, bean beetles, and carrot flies
- Thyme: Deters cabbage worms and whiteflies
- Lemongrass: Repels mosquitoes and other insects
Flowering Plants
- Marigolds: Repel nematodes and many insects; their roots release compounds that kill harmful nematodes
- Nasturtiums: Act as trap crops for aphids and attract beneficial insects
- Sunflowers: Attract pollinators and provide habitat for beneficial insects
- Cosmos: Attract beneficial insects like lacewings and hoverflies
- Amaranth: Attracts predatory ground beetles
Vegetables and Other Plants
- Onions and garlic: Repel many pests with their strong odor
- Chili peppers: Deter many insects when interplanted or used in sprays
- Cassava: Intercropped with other plants to reduce pest pressure
- Pigeon peas: Attract beneficial insects and can be used as trap crops
- Desmodium: Repels stem borers in cereal crops (push-pull system)
Companion Planting Chart for Common African Garden Crops
| Crop |
Good Companions |
Poor Companions |
Pest Protection |
| Tomatoes |
Basil, marigolds, nasturtiums, onions, garlic, carrots |
Potatoes, cabbage family, fennel |
Whiteflies, aphids, tomato hornworm |
| Maize (Corn) |
Beans, squash, pumpkin, cucumber, amaranth |
Tomatoes |
Corn earworm, stem borers |
| Beans |
Maize, amaranth, carrots, cabbage, marigolds |
Onions, garlic, peppers |
Bean beetles, aphids |
| Cabbage Family |
Aromatic herbs, nasturtiums, onions, marigolds |
Strawberries, tomatoes, beans |
Cabbage worms, aphids |
| Okra |
Peppers, eggplant, cowpeas, sweet potatoes |
Root vegetables |
Aphids, stink bugs |
| Peppers |
Basil, onions, carrots, marigolds |
Beans, kale |
Aphids, spider mites |
| Sweet Potatoes |
Marigolds, nasturtiums, oregano |
Squash family |
Sweet potato weevil |
| Amaranth |
Maize, onions, carrots |
None significant |
Attracts beneficial insects |
| Cassava |
Maize, beans, groundnuts |
Citrus |
Cassava mealybug |
| Eggplant |
Beans, marigolds, thyme, tarragon |
Fennel |
Flea beetles, aphids |
Traditional African Companion Planting Systems
Three Sisters Planting (Adapted)
Based on the traditional Native American system but adapted for African contexts:
- Maize: Provides support for climbing plants
- Beans or cowpeas: Fix nitrogen in soil and climb maize stalks
- Squash or pumpkin: Provide ground cover to suppress weeds and retain moisture
- Optional fourth sister: Amaranth or sunflowers to attract beneficial insects
Push-Pull System
Developed in East Africa for cereal crop protection:
- Push: Desmodium planted between rows of maize or sorghum repels stem borers
- Pull: Napier grass planted around the field's border attracts stem borers away from the main crop
- Additional benefits include soil improvement and fodder production
Implementing Companion Planting in Your Garden
Identify Key Pests
Determine which pests are most problematic in your garden and focus on companion plants that address those specific issues.
Plan Your Layout
Design your garden with companion relationships in mind. Consider using intercropping, border plantings, or strategic placement of companion plants throughout the garden.
Consider Timing
Plant companions at the appropriate time so they're effective when needed. Some companions should be established before the main crop, while others can be planted simultaneously.
Maintain Diversity
Include a variety of plant families and types to create a balanced ecosystem that naturally limits pest populations.
Observe and Adapt
Keep records of which combinations work well in your specific conditions and adjust your planting plan accordingly in future seasons.
Companion Planting Arrangements
Intercropping
Planting compatible crops in alternating rows or mixed together in the same row.
Example: Alternating rows of maize and beans, with marigolds at the ends of rows.
Border Planting
Surrounding vulnerable crops with protective companion plants.
Example: Planting aromatic herbs around the perimeter of a vegetable bed.
Trap Cropping
Planting attractive crops to lure pests away from main crops.
Example: Planting nasturtiums to attract aphids away from vegetables.
Nurse Cropping
Using one plant to create favorable conditions for another.
Example: Tall sunflowers providing afternoon shade for heat-sensitive greens.
Troubleshooting Tips
- If companion planting doesn't seem effective, check plant spacing—companions may need to be closer to provide protection
- Some benefits take time to develop as beneficial insect populations increase
- Companion effects may be subtle; use multiple pest management strategies together
- Local adaptations may be necessary—observe what works in your specific environment
- Maintain healthy soil to maximize plant resilience and companion planting benefits
Beyond Companion Planting
For best results, combine companion planting with other natural pest management strategies:
- Crop rotation to break pest cycles
- Physical barriers like row covers when needed
- Healthy soil management to promote plant resilience
- Timely harvesting to prevent pest buildup
- Manual removal of pests when populations are small
- Botanical sprays for targeted pest control when necessary
