Good Companions
Basil
Carrots
Marigolds
Avoid
Fennel
Cabbage
Corn
Companion planting is the practice of growing different plant species in proximity to gain mutual benefits — improving pollination, controlling pests, enriching soil, and increasing yields. It is one of the oldest agricultural techniques in the world, with evidence of companion planting going back thousands of years. The famous 'Three Sisters' system developed by Indigenous peoples of North America (corn, beans, and squash grown together) is perhaps the most studied example: corn provides a trellis for beans, beans fix nitrogen that feeds corn and squash, and squash leaves shade the ground to suppress weeds and retain moisture. Studies from the Rodale Institute and Cornell University have found that properly designed companion planting combinations can reduce pest pressure by 30–50%, increase crop yields by 10–30%, and reduce fertilizer needs significantly. The calculation aspect of companion planting involves spacing — ensuring companion plants don't compete excessively for light and root space while still providing their benefits. This guide helps you determine which plants pair well, which to keep separated, and the optimal spacing for companion plantings in your garden beds.
Companion Spacing = (Plant A Mature Width / 2) + (Plant B Mature Width / 2) + 2 inches Plants per 100 sq ft = 100 / (Spacing in ft)^2
- 1Step 1: List the primary crops you are growing and their known companion plant needs.
- 2Step 2: Identify beneficial companions from the reference table and any plants to avoid.
- 3Step 3: Calculate spacing for each pair based on mature plant widths plus a buffer.
- 4Step 4: Plan your garden layout so each crop is within 2–3 feet of its companion for pest-repellent effects.
- 5Step 5: Include at least one flowering plant per 10 sq ft of vegetable garden to attract beneficial insects.
- 6Step 6: Avoid placing allelopathic plants (like fennel) near sensitive crops — fennel inhibits most vegetables.
Basil's volatile oils are believed to repel common tomato pests. Plant 1 basil plant between every 2 tomato plants. Basil also improves tomato flavor according to gardening tradition, though scientific evidence is mixed.
Classic Native American system. Corn planted first, then beans planted 1 inch from corn base after corn reaches 4–5 inches tall, then squash in same hill. Beans fix nitrogen (50–100 lbs N/acre/year), corn provides trellis, squash shades ground.
French marigolds (Tagetes patula) emit compounds from roots that deter nematodes and their foliage scent confuses aphids. Nasturtiums attract aphids away from vegetables as trap crops. Plant at all four corners and along the perimeter.
Carrot fly and onion fly are each repelled by the scent of the other's companion. Alternate rows of carrots and onions confuses both pests. This classic European companion combination has been used for centuries.
Planning vegetable garden layouts to maximize natural pest control. This application is commonly used by professionals who need precise quantitative analysis to support decision-making, budgeting, and strategic planning in their respective fields
Designing polyculture garden beds with complementary plant combinations. Industry practitioners rely on this calculation to benchmark performance, compare alternatives, and ensure compliance with established standards and regulatory requirements, helping analysts produce accurate results that support strategic planning, resource allocation, and performance benchmarking across organizations
Selecting companion flowers to attract pollinators to vegetable crops. Academic researchers and students use this computation to validate theoretical models, complete coursework assignments, and develop deeper understanding of the underlying mathematical principles
Researchers use companion planting guide computations to process experimental data, validate theoretical models, and generate quantitative results for publication in peer-reviewed studies, supporting data-driven evaluation processes where numerical precision is essential for compliance, reporting, and optimization objectives
Allelopathic Plants — Isolation Required
{'title': 'Allelopathic Plants — Isolation Required', 'body': 'Several plants produce chemicals that inhibit neighboring plant growth: fennel (inhibits most vegetables), black walnut (juglone inhibits tomatoes, peppers, many plants within 50 ft), sunflowers (can inhibit pole beans), and sorghum cover crops (suppress germination for months after incorporation). Always check allelopathy before planting.'}
Dynamic Accumulators
{'title': 'Dynamic Accumulators', 'body': "Some companion plants are 'dynamic accumulators' — plants with deep roots that mine nutrients from subsoil and concentrate them in their leaves. Comfrey, dandelion, and yarrow accumulate potassium, calcium, and phosphorus. Chop these plants and use as mulch or compost tea to recycle nutrients to shallow-rooted crops. Comfrey is exceptionally useful in permaculture systems."}
Negative input values may or may not be valid for companion planting guide depending on the domain context.
Some formulas accept negative numbers (e.g., temperatures, rates of change), while others require strictly positive inputs. Users should check whether their specific scenario permits negative values before relying on the output. Professionals working with companion planting guide should be especially attentive to this scenario because it can lead to misleading results if not handled properly. Always verify boundary conditions and cross-check with independent methods when this case arises in practice.
| Main Crop | Good Companions | Bad Companions | Benefit |
|---|---|---|---|
| Tomatoes | Basil, marigolds, carrots, parsley | Fennel, brassicas, corn | Pest repellent, pollinator |
| Beans | Carrots, cucumber, squash, marigolds | Onions, fennel, garlic | Nitrogen fixation |
| Carrots | Onions, leeks, sage, rosemary | Dill, fennel | Pest confusion |
| Brassicas | Dill, sage, rosemary, onions | Tomatoes, peppers, grapes | Pest repellent |
| Corn | Beans, squash, cucumber | Tomatoes | Three Sisters synergy |
| Squash | Corn, beans, nasturtiums, radish | Potatoes | Ground cover, pollination |
| Roses | Garlic, lavender, marigolds, chives | Fennel | Aphid repellent |
| Lettuce | Radish, carrots, chives, onions | Celery | Spacing, bolt delay |
Does companion planting actually work?
Research on companion planting is mixed. The Three Sisters system has strong scientific support — nitrogen fixation by legumes is well-documented. Marigolds reducing nematode pressure in soil is also well-supported. Scent-based pest confusion effects (basil/tomato, carrot/onion) have moderate support. Many traditional companion planting claims are based on observation rather than controlled research, but experienced gardeners report real benefits.
Why is fennel a bad companion for most vegetables?
Fennel produces allelopathic chemicals from its roots and foliage that inhibit the germination and growth of most vegetable crops, including tomatoes, peppers, beans, and kohlrabi. Keep fennel in its own container or a separate bed away from vegetable gardens. The only good companions for fennel are other fennel plants. This matters because accurate companion planting guide calculations directly affect decision-making in professional and personal contexts.
How do cover crops differ from companion plants?
Cover crops are grown primarily to benefit the soil (nitrogen fixation, erosion control, organic matter addition) and are typically incorporated into the soil before the main crop is planted. Companion plants grow simultaneously with the main crop, providing benefits through chemical, physical, or biological interactions throughout the growing season. The process involves applying the underlying formula systematically to the given inputs.
What flowers are best for attracting beneficial insects?
Phacelia, dill, fennel, cilantro (allowed to flower), sweet alyssum, borage, and buckwheat attract the most beneficial insects — lacewings, parasitic wasps, and hoverflies that control aphids and caterpillars. Plant them in border strips at least 2 feet wide throughout the garden for maximum effect. This is an important consideration when working with companion planting guide calculations in practical applications. The answer depends on the specific input values and the context in which the calculation is being applied.
Can I plant garlic and onions everywhere as pest repellents?
Garlic and onions do repel some pests and have antifungal properties in the soil, but they should not be planted near beans or peas, which they inhibit. They are excellent companions for roses (repel aphids), brassicas, and fruit trees. Plant garlic around the perimeter of vegetable beds or interplanted with susceptible crops.
What is trap cropping?
Trap cropping deliberately plants a sacrificial crop that pests prefer over the main crop. Nasturtiums attract aphids, protecting adjacent plants. Blue Hubbard squash attracts squash beetles, protecting other squashes. The trap crop is then removed with the pest load or treated while the main crop remains undamaged. In practice, this concept is central to companion planting guide because it determines the core relationship between the input variables.
How wide does a companion strip need to be to be effective?
For pollinator and beneficial insect attraction, flowering strips should be at least 2–3 feet wide and as long as practical. For pest-repellent effects, a single row of companion plants adjacent to the crop has some benefit, but denser plantings of 3+ rows or intermixed planting provides much stronger effects. The process involves applying the underlying formula systematically to the given inputs.
Pro Tip
Plant sweet alyssum (Lobularia maritima) as a border around all vegetable beds. It blooms continuously, requires no care, costs just pennies per plant from seed, and attracts more beneficial insect species than almost any other companion plant — hoverflies, parasitic wasps, and lacewings that provide free biological pest control all season.
Did you know?
The Three Sisters companion planting system — corn, beans, and squash — was so productive that it supported the rise of large civilizations across North America. Archaeobotanists estimate this system was developed at least 5,000 years ago in Mesoamerica. Studies show the Three Sisters system produces 20% more calories per acre than any single crop grown alone on the same plot.