Bok Choy Companion Plants
Brassica rapa subsp. chinensis · mustard family family · rotation group: brassica
The best companion plants for bok choy are Sweet alyssum, White clover (undersown living mulch), Mustard (border trap crop), Yellow rocket (dead-end trap crop), and Lettuce. Avoid planting bok choy near Other brassicas, Strawberry, Pole bean. Of the 11 pairings recorded here, 4 are supported by published research and 6 are traditional practice with no controlled evidence behind them.
What to plant with bok choy
| Plant | Claimed benefit | Evidence | What the evidence actually shows |
|---|---|---|---|
| Mustard (border trap crop) | A perimeter row of mustard draws harlequin bugs and other brassica bugs off the choy. | Research-backed | Field trials with mustard as a perimeter trap crop for collard held leaf damage under 1% in spring, and a 2.3 m gap between trap and cash crop cut egg-laying on the cash crop about fourfold versus an adjacent trap row. Trap cropping only works with scouting — pests must be killed on the trap plants or they spill back into the crop. |
| Sweet alyssum | Alyssum flowers alongside the crop recruit hoverflies, lady beetles and parasitoid wasps that hit brassica aphids and caterpillars. | Research-backed | In replicated organic cabbage plots, insectary alyssum significantly increased parasitism of a brassica caterpillar and the abundance of predatory coccinellid eggs and larvae. Separate laboratory work confirms alyssum volatiles attract the diamondback moth parasitoid and that its flowers extend parasitoid lifespan and egg-laying — but that part is cage work, not field yield data. |
| White clover (undersown living mulch) | A low living clover mulch between bok choy plants reduces cabbage root fly egg-laying and aphid colonisation. | Research-backed | Reduced cabbage root fly egg counts in clover-undersown brassicas is a repeated result. The critical detail: dead brown clover gave no benefit while live green clover did, so the effect is host-finding disruption by green background, not chemical repellency. Clover competes strongly for water and nitrogen in a crop this shallow-rooted, so sow it only after the choy is well established. |
| Yellow rocket (dead-end trap crop) | Yellow rocket planted at the edge attracts diamondback moth to lay eggs where the larvae cannot survive. | Research-backed | Screenhouse trials found diamondback moth laid 19-300x more eggs on yellow rocket than on cabbage in no-choice tests, with zero larval survival on it versus 22-24% on cabbage — a genuine dead-end trap. Caveats: the work was in screenhouses rather than open fields, and yellow rocket is a weedy biennial that can become a management problem itself. |
| Dill | Dill's flat flower heads feed the small parasitoid wasps that attack brassica pests. | Traditional | The nectar mechanism is real and general for flowering insectary plants, but the species actually tested in brassica systems are sweet alyssum and buckwheat. Dill in particular has not been trialled here, and the same extension charts that recommend flowers list dill as a plant to keep away from cabbage-family crops. |
| Lettuce | Fast lettuce fills the gaps between choy plants and is harvested before they size up. | Traditional | Purely a spacing and timing convenience, with no measured pest or growth effect. Both are cool-season, shallow-rooted and share the same succession schedule, so they can share a bed and a row cover. |
| Onion | Alliums interplanted with cabbage-family crops are said to mask them from cabbage moths and aphids. | Traditional | Widely printed on extension companion charts, but no replicated trial shows an allium interplant protecting brassicas. Where masking effects have been measured in other crop pairs they were density-dependent and short-lived, needing far more allium than a garden row provides. |
| Thyme | Aromatic thyme is said to repel cabbage moths and flea beetles from bok choy. | Not supported | Tested and not supported as stated. Experiments comparing aromatic and non-aromatic companion plants around brassicas found aromatics were no more effective than plain green plants, and desiccated plants gave no protection at all — the reduction in egg-laying tracks green ground cover, not aroma. Interplanting thyme may still help slightly, but not for the reason the folklore gives. |
What not to plant with bok choy
| Plant | Claimed problem | Evidence | What the evidence actually shows |
|---|---|---|---|
| Other brassicas | Blocking bok choy in with cabbage, broccoli and kale concentrates the shared pest complex and soil diseases. | Traditional | The disease half is standard extension practice — clubroot, black rot and Alternaria survive in soil and debris, so brassicas are rotated out of a bed for several years. The adjacency effect within a single season is a reasonable inference from that, not a measured result. Bok choy is a magnet for flea beetles and cabbage maggot, so it will also amplify pressure on neighbouring cole crops. |
| Pole bean | Pole beans are listed as a plant to avoid near cabbage-family crops. | Traditional | No trial data exists for this pairing. The defensible objection is physical rather than chemical: a bean trellis shades a bed that a heat-sensitive crop like bok choy needs kept cool and open, and it makes row cover impossible. |
| Strawberry | Strawberries appear on extension charts as a plant to keep away from cabbage-family crops. | Traditional | Chart folklore with no supporting trial; the publication itself notes companion planting is not an exact science and that results vary. Ironically the only relevant measured result runs the other way — Purdue observed strawberries interplanted with sweet alyssum carrying almost no aphids. |
The honest verdict
Of everything gardeners recommend planting alongside bok choy, 4 pairings have been tested properly: Sweet alyssum, White clover (undersown living mulch), Mustard (border trap crop), Yellow rocket (dead-end trap crop). Those are the ones worth planning your bed around.
The remaining 3 pairings on this page are traditional practice. They circulate on every companion planting chart online, but we could not find controlled evidence testing them. They are not wrong so much as unverified — most cost nothing to try, and interplanting flowers and herbs has its own well-documented benefit of pulling pollinators and predatory insects into the garden.
Widely repeated, not supported: Thyme — Tested and not supported as stated. Experiments comparing aromatic and non-aromatic companion plants around brassicas found aromatics were no more effective than plain green plants, and desiccated plants gave no protection at all — the reduction in egg-laying tracks green ground cover, not aroma. Interplanting thyme may still help slightly, but not for the reason the folklore gives.
Every row above links to the publication it came from. See how we grade evidence.
Growing bok choy: the numbers
| Sun | Full sun (6+ hours) |
|---|---|
| Water | Moderate |
| Spacing | 8 in apart · 18 in between rows · 2 per square foot |
| Mature size | about 12 in tall |
| Soil pH | 6–7.5 |
| Days to maturity | 30–60 days |
| Frost tolerance | Half-hardy — takes a light frost |
| Containers | Yes — 2 gallon minimum |
| Typical yield | 1 head |
| Common pests | flea beetle, imported cabbageworm, cabbage looper, diamondback moth, cabbage maggot, aphid, slug |
| Common diseases | Alternaria leaf spot, black rot, clubroot |
When to plant bok choy
Zone 6b shownStart seeds indoors: Feb 27 – Mar 13 — 4–6 weeks before your last frost
Transplant outdoors: Mar 27 – Apr 9 — 2 weeks before last frost
Direct sow outdoors: Mar 27 – Apr 9 — 2 weeks before last frost
Expected harvest: Apr 26 – May 26 — 30–60 days from planting
Fall planting: Sep 1 – Sep 14 — 8 weeks before your first fall frost
Those dates are for zone 6b. Get your own dates by ZIP code →
Varieties worth knowing
seeds- Joy Choi — White-stalked pak choi listed by Mississippi State University Extension; standard full-size type.
- What-A-Joy — Pak choi hybrid listed by Mississippi State University Extension; compact plant suited to close spacing.
- Fen Jen — Listed by UC Master Gardeners of Santa Clara County as a variety suited to mild-winter California gardens.
- San Fan — Listed by UC Master Gardeners of Santa Clara County among varieties recommended for local fall and early-spring sowings.
Variety names link to seeds on Amazon. As an Amazon Associate we earn from qualifying purchases. These are the varieties named in the extension sources for this crop, not a paid placement — where a source recommended a variety for a specific reason, that reason is the note beside it.
Put it in a bed
The garden planner checks every square against this ledger as you place crops — if you drop bok choy next to something recorded as a bad neighbour, the square turns red and tells you why.
Records for the plants named above:
Same rotation group (brassica) — don't follow one with another:
Bok Choy companion planting questions
What should not be planted next to bok choy?
How far apart should bok choy be planted?
Does companion planting with bok choy actually work?
When should I plant bok choy?
Sources for this record
- UMN Extension — Growing Chinese cabbage and bok choy in home gardens
- UC Master Gardeners of Santa Clara County — Bok Choy
- NC State Extension Plant Toolbox — Brassica rapa (Chinensis Group)
- Mississippi State University Extension — Cabbage, Chinese
- NC State Extension Gardener Handbook — Vegetable Gardening
Record compiled 2026-07. Spot an error or a study we missed? Tell us and we'll correct the entry.