Companion Planting Engine

Companions is an AI companion planting tool for choosing plants to grow together and understanding how neighbouring plants affect one another.

Name the plants already growing, the plants to be added, or the mixed planting being planned, and Companions determines which combinations are likely to work, which may cause problems, and why a particular combination is beneficial, neutral or competitive.

Bring a companion-planting claim instead, and Companions states whether the relationship is supported and what mechanism is supposed to produce the effect.

companion planting checker

• Evaluates a pair or group of plants for compatibility, competition and useful interactions within the same growing space.

companion planting chart

• Identifies plants to keep apart.
• States whether the reason for separation is strong competition, growth suppression, shared damaging pressures or an unsuitable physical arrangement.

plant interaction reader

• Names the mechanism behind a pairing: pollinator support, pest diversion, root partitioning, shade, living cover, nitrogen fixation, allelopathy or resource competition.

guild builder

• Builds a guild or mixed planting around a crop, fruit tree or growing space by matching plants to useful ecological roles.

garden planner and plant spacing calculator

• Arranges those roles in the bed so each one can function.

trap crop and insectary plant finder

• Identifies trap crops, insectary plants and mixed-planting strategies that influence pests through attraction, diversion or support for beneficial insects.

root and mycorrhizal association lookup

• Examines root depth, root competition, mycorrhizal relationships, nutrient cycling and root exudates below the soil surface.

polyculture and traditional lineage guide

• Explains established polycultures such as Three Sisters, including the function of each component plant.
• States the lineage of a traditional planting system where the lineage is known.

companion planting evidence checker

• Separates well-supported mechanisms from plausible but uncertain relationships and from repeated gardening claims with limited evidence.

failed pairing diagnosis

• Diagnoses why a supposedly compatible pairing is underperforming in actual growing conditions.

Enter one plant, two plants, a group of plants, or the growing system to be built.

For a designed mixed planting, name the main crop or tree and what the surrounding plants should accomplish: pollination, pest pressure, ground cover, nitrogen fixation, living support, soil protection or several functions together.

Include climate, available space, planting density, irrigation, soil conditions and time of year, since those conditions determine whether an otherwise compatible combination works.

find what grows well together

questions people ask:

"What grows well with tomatoes?" · "Can peppers grow beside beans?" · "What suits an underplanting beneath blueberries?" · "Do carrots and onions grow well together?"

find what to keep apart

questions people ask:

"What should not be planted near fennel?" · "Why do walnut trees suppress nearby plants?" · "Does mint compete with everything around it?" · "Should brassicas follow strawberries in the same bed?"

build a guild or mixed planting

questions people ask:

"How do I build a guild around an apple tree?" · "How does a Three Sisters planting work?" · "What belongs in a mango tree guild?" · "Plan a mixed bed around asparagus."

choose a functional companion

questions people ask:

"Which plants fix nitrogen?" · "What makes a good living mulch under fruit trees?" · "What is a nurse plant?" · "Which cover crop should precede sweetcorn?"

plant for pests and beneficial insects

questions people ask:

"What is a good trap crop for squash bugs?" · "Which flowers attract hoverflies?" · "Do marigolds suppress nematodes?" · "What draws lacewings into a vegetable plot?"

check roots and allelopathy

questions people ask:

"What is allelopathy?" · "Do deep-rooted and shallow-rooted plants compete?" · "Which plants share mycorrhizal fungi?" · "How long should I wait after terminating cereal rye?"

test a companion planting claim

questions people ask:

"Is companion planting scientifically proven?" · "Does basil improve tomato flavour?" · "Is garlic actually good for roses?" · "Does borage deter hornworm?"

diagnose a failing pairing

questions people ask:

"Why is lettuce struggling beside sunflowers?" · "Why is comfrey taking over a bed?" · "Why did a nasturtium interplanting make no difference?" · "Is 30cm too close for courgettes and sweetcorn?"

the pairing and the verdict

• the plant, pairing or mixed planting being assessed;
• whether the relationship is beneficial, neutral, competitive or unsuitable;
• the mechanism responsible for the interaction;

what is happening above and below ground

• competition for light, water, nutrients, root space or canopy space;
• allelopathic effects where credible evidence supports them;
• root depth, root-zone overlap and below-ground compatibility;
• mycorrhizal or other rhizosphere relationships where relevant;

nutrient and insect functions

• nitrogen-fixing or nutrient-cycling roles and when those benefits become available;
• pollinator, predator or parasitoid support;
• trap-crop or pest-diversion functions;

where each plant goes

• spacing, buffer, border, canopy or placement guidance;
• the role of each species within a guild or polyculture;
• traditional lineage where the planting system has a documented cultural or regional origin;

how strong the evidence is

• an evidence note distinguishing established mechanisms from uncertain or folklore-heavy claims;

what to change next

• follow-up options for modifying the planting around the actual crop, site or problem.

why a pairing chart is not an answer

The mechanism matters more than the pairing chart. Two plants are not companions because their names appear together on a list; what matters is the expected interaction and whether the growing conditions allow that interaction to operate.

why most antagonism is crowding

Competition explains many supposed antagonisms. Plants sharing the same root zone, moisture supply, canopy level or nutrient demand suppress one another without any chemical incompatibility, and spacing can turn a poor pairing into a workable one.

when chemical suppression is the actual cause

Allelopathy is real but should not be assumed. Some plants and residues chemically inhibit other species, and allelopathy is distinguished from ordinary crowding, resource competition and unsuitable site conditions.

what a legume gives its neighbour, and when

Nitrogen fixation does not deliver instant fertilizer to a neighbour. Legumes primarily use fixed nitrogen themselves, and much of the wider benefit arrives as roots, leaves and residues turn over.

why the design unit is a role rather than a species

Guilds are built from functions. The useful design unit is the role — ground cover, pollinator support, nitrogen fixation, living support or pest diversion — rather than one supposedly mandatory companion species.

what an unmanaged trap crop becomes

Trap crops require active management. A plant that attracts pests away from the main crop helps only while the concentrated pest population is monitored and controlled; otherwise the trap crop becomes another source of infestation.

why the bed has a calendar as well as a layout

Mixed planting has a time dimension as well as a spatial one. What grew in the bed previously, when a cover crop was terminated, when flowers begin blooming and when neighbouring plants reach full size can matter as much as what stands beside the crop today.

why one proven mechanism proves nothing about another

The evidence is relationship-specific. Intercropping, floral insect support, trap cropping, allelopathy, nitrogen fixation and traditional polycultures each carry their own evidence, so each mechanism is evaluated separately.

the relationships plants form when grown together

Plants growing together form several kinds of relationship:

• specific plant pairings: whether two named species are compatible, beneficial, neutral or competitive;
• good and bad neighbours: what grows well beside a crop and what should be separated from it;
• guilds and plant communities: multi-species systems built around complementary ecological functions;
• traditional polycultures: Three Sisters and other established Indigenous, historical and regional mixed-growing systems;
• functional companion roles: nurse plants, trap crops, cover crops, living mulch, insectary plants and living supports;
• nutrient relationships: nitrogen fixation, biomass cycling and the timing of nutrient availability;
• allelopathy: chemical suppression associated with living plants or plant residues;
• root interactions: rooting depth, below-ground competition, mycorrhizal associations and resource partitioning;
• resource competition: competition for light, moisture, nutrients, root volume and physical space;
• pest-management planting: trap cropping, crop diversification and plantings that support predators and parasitoids;
• pollinator support: plants providing useful bloom timing, nectar or pollen around crops that benefit from insect activity;
• mixed-bed layout: spacing, canopy position, root zones, borders and placement within companion systems;
• failed companion systems: why a supposedly compatible pairing underperforms in actual growing conditions;
• evidence questions: whether a companion claim rests on research, a credible biological mechanism, traditional practice or repetition alone.