Cosmos growing profile.

Cosmos Companion Plants

What may help, what can compete, and where the evidence is still uncertain.

Cosmos Cosmos bipinnatus

Warm-season flower in the daisy family. View plant profile →

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Quick answer

No reviewed study supports a specific beneficial companion for cosmos yet. 1 traditional pairing is listed separately because the review found no adequate evidence.

Every status below has a direction, mechanism, context and source. "No verified relationship" means we looked and found nothing usable; the planner then evaluates spacing, light, water and timing normally. How we classify evidence →

Traditional claim (1)

Never a hard rule; may appear as an optional experiment.

Traditional claims are shown separately because repetition across charts is not evidence. They never change a planner score; treat them as optional experiments.

TomatoSolanum lycopersicumTraditionalSupports beneficial insects Cosmos may affect TomatoSummer · arrangement unspecifiedTier D Review: August 15, 2026

Why?

Claim. Cosmos is said to attract beneficial insects that protect tomatoes. Cosmos flowers do feed hoverflies and bees, but no tomato outcome has been measured.

Mechanism. Proposed by tradition; not demonstrated in a controlled comparison.

Conditions. Planted together Both plants must be present at the same time.

Applies when. Optional experiment, not a guarantee.

Limitations. General insectary value only.

Evidence. Tier D: Traditional knowledge or structured community observations without a controlled comparison. (tradition).

Sources. University of Minnesota Extension 2023

Reviewed August 15, 2026 by Garden Planner editorial team (pending independent horticultural review). Record cosmos--tomato--insectary_support v1. Request a correction.

**A realistic garden scene where cosmos grows beside a plant with a traditional or unknown relationship.**Coexistence in a photograph is not evidence that the plants affect each other.

Example layout for cosmos

No supported or conditional relationship specifies a layout. Space cosmos at 30–45 cm and plan by light, water and timing.

**Side view of cosmos (60–150 cm) beside typical companions, showing canopy, support, shade and access.**

When these companions overlap

Bed occupancy in Portland, Oregon (estimates). A relationship only matters while both plants are present.

Cosmos

Tomato30 wk overlap

Overlap in weeks
Tomato	30 weeks

Crop rotation guidance

Rotation is about what occupied the bed in previous seasons and is calculated separately from the live companion relationships above.

Rotate cosmos on a 1-year cycle with other daisy family crops (Lettuce, Sunflower, French marigold, Calendula). Shared risks: lettuce downy mildew, aphids, slugs on lettuce.

Crop rotation hub · Asteraceae family page

Physical and resource fit

Tomato: Different water needs.

Fit checks come from plant attributes and apply even when a pairing has a positive claim.

Community observations (anecdotal)

These reports come from gardeners and are not reviewed evidence. Results vary with soil, climate and practice. Community data never changes an evidence tier or a planner score.

Reports for cosmos: 0 (community submissions open in a later phase; drafts are stored only on your device).

**Community-submitted photo area (moderated) with context fields: region, season, layout, varieties, outcome.**

Record an observation

Evidence summary and sources

Companion planting in home gardens — University of Minnesota Extension, 2023 (guidance)

Reviewer: Garden Planner editorial team (pending independent horticultural review). Status counts on the Companions A–Z page are derived from these records. Corrections.

Cosmos Companion Plants

Quick answer

Traditional claim (1)

No records match those filters

Example layout for cosmos

When these companions overlap

Crop rotation guidance

Physical and resource fit

Community observations (anecdotal)

Evidence summary and sources

Related

Visual evidence on this page

Our Methodology & Sources