Kale companion plants: brassicas need help

Kale (*Brassica oleracea* var. *sabellica*) is among the most heavily attacked vegetables in the home garden. Imported cabbageworm (*Pieris rapae*), cabbage looper (*Trichoplusia ni*), diamondback moth (*Plutella xylostella*), and aphids -- primarily cabbage aphid (*Brevicoryne brassicae*) -- treat.

—- title: "Kale companion plants: brassicas need help" slug: kale-companion-plants hub: care category: "Companion planting" description: "Kale attracts specialist brassica pests that strip leaves fast. These companion plants reduce pressure through pest confusion, trap cropping, and beneficial insect support." date: 2026-06-10 updated: 2026-06-10 author: "Thomas A." reading_time: 9 release_after: 2026-06-29 —-

Kale (Brassica oleracea var. sabellica) is among the most heavily attacked vegetables in the home garden. Imported cabbageworm (Pieris rapae), cabbage looper (Trichoplusia ni), diamondback moth (Plutella xylostella), and aphids — primarily cabbage aphid (Brevicoryne brassicae) — treat kale as a primary host. Because kale is typically grown over a long season (spring through fall frost and sometimes beyond), the pest window is long.

Companion planting for kale works on three mechanisms: aromatic masking of glucosinolate signals, provision of nectar and habitat for parasitic insects, and trap cropping.

The companion planting table

Understanding the glucosinolate signal

Per NC State Extension, glucosinolates are sulfur-containing compounds that give brassica crops their characteristic flavor. Cabbage white butterflies and other specialist brassica pests use these chemical signals to locate host plants from a distance. Dense plantings of aromatic herbs introduce competing volatile signals that partially mask the brassica cue.

The practical effect in field trials has been inconsistent — some studies show meaningful reductions in egg-laying rates; others show minimal effect at the planting densities typical in home gardens. Per Cornell Cooperative Extension, aromatic companions should be seen as a supplement to, not a replacement for, floating row cover and monitoring.

Building a beneficial insect community

The most evidence-based use of companion plants is creating habitat for beneficial insects. Per UC IPM, Cotesia glomerata — a parasitic wasp — is one of the most important biological controls for imported cabbageworm. It requires nectar sources as adult food. Dill, cilantro, parsley, and sweet alyssum in flower provide these resources.

For kale specifically, establishing a mix of umbellifer herbs (dill, cilantro) that flower continuously through the season maintains parasitoid populations from spring through fall. Per Oregon State Extension, succession planting of cilantro (every 3 weeks) ensures continuous bloom, as cilantro bolts quickly and the bloom window per sowing is short.

Trap cropping with nasturtium

Nasturtiums are a practical trap crop for cabbage aphid and black bean aphid. The aphids colonize nasturtiums more readily than kale, especially early in the season. Per Clemson HGIC, the strategy works only if you monitor the nasturtiums regularly and remove infested plants before the colony collapses and moves. A nasturtium left to die from aphids provides no benefit — it just extends the aphid lifecycle.

Plant nasturtiums upwind of kale rows and check them weekly beginning when average temperatures reach 60°F.

Aphid management: the real problem for kale

Kale can tolerate moderate aphid pressure, but heavy infestations of cabbage aphid — which cluster densely on stems and the undersides of leaves — stunt growth and make the crop unpalatable. Per Rutgers NJAES, the most effective companion-planting-adjacent strategy is maintaining sweet alyssum as a living mulch along row edges. Syrphid fly larvae can consume hundreds of aphids per larva before pupating.

This does not eliminate aphids but can prevent the population spikes that cause economic damage. When aphid colonies are already established, a strong jet of water to dislodge them and targeted applications of insecticidal soap remain faster interventions.

Planting arrangement for a 4-foot raised bed

Per Penn State Extension, an effective companion arrangement for a 4-foot-wide kale bed:

• Kale transplants spaced 18–24 inches apart in two rows
• Sweet alyssum seeded along both long edges of the bed
• Dill or cilantro planted at the corners, where they won't shade the kale
• Nasturtiums placed 12–18 inches outside the bed edges (in adjacent paths or a border strip)
• Thyme at the front edge of the bed as a decorative and functional border

Frequently asked questions

Does mint actually deter pests from kale? The evidence is anecdotal. Per NC State Extension, mint's volatile compounds are reputed to deter several insects, but controlled trials showing meaningful reductions in brassica pest damage from nearby mint plantings are lacking. Mint is high-risk as a garden plant due to its aggressive spreading habit — plant it only in containers near kale beds. If you're going to try it, use spearmint or peppermint, which have stronger volatile profiles.

Can I grow kale and broccoli next to each other? You can, but doing so increases the concentration of glucosinolate signals in one area and amplifies pest pressure on both crops. Per Oregon State Extension, alternating brassica crops with non-host plants (even just a 12-inch strip of marigolds) provides more pest dilution than planting brassicas in a continuous block.

What is the best companion plant for fall kale specifically? For fall kale, nasturtiums have often declined by the first frost and are less useful. For fall plantings, thyme and sage — as established perennial edges — provide the most consistent benefit by masking plant signals from still-active moths. Per Penn State Extension, fall populations of imported cabbageworm are lower than spring peaks but still significant, particularly in warm zones (6–8).

Does dill compete with kale? Not significantly. Dill has a taproot that does not compete with the fibrous roots of kale. The main risk with dill is shading: mature dill can reach 3–4 feet and should be planted to the north of kale rows in northern hemisphere gardens to avoid casting shade on the main crop. Per Cornell Cooperative Extension, the pollinator and parasitoid benefit of dill in flower outweighs any competition concern.

Sources

1. NC State Extension — Brassica Companion Planting
2. Cornell Cooperative Extension — Vegetable Gardening
3. UC IPM — Biological Control for Vegetable Gardens
4. Oregon State Extension — Companion Planting
5. Clemson HGIC — Companion Planting
6. Rutgers NJAES — Aphid Management in Brassicas
7. Penn State Extension — Vegetable Companion Planting