Purple Yu Choy Sum
Purple Yu Choy Sum is a vegetable in the Brassicaceae family. It grows best in full sun to part shade with medium moisture, and is listed for USDA zones 2-13. Plants reach harvest about 42–58 days after planting and sit about 6 inches apart.
Varieties
1 from True Leaf Market · sorted by days to maturity▸Kosaitai - Hon Tsai Tai42–58 days
Heirloom; Container; Vegetable; Annual
Yu Choy Sum Seeds - Kosaitai - Hon Tsai Tai. Heirloom, Non-GMO. Brassica rapa var purpurea. 50 days. Cool season annual. This flowering purple stem choy sum, also known as kosaitai or hon tsai tai, is a popular Chinese specialty vegetable. The leaf stalks and veins are purple while the leaves are dark green and the flowers are yellow. ~ 10,200 seeds / oz.
View on True Leaf Market ↗
Plant spacing
In a square-foot bed, space purple yu choy sum about 6 in apart — that fits 4 plants in each 1-foot square (2×2). Wider rows or containers space the same.
Plan your purple yu choy sum planting
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Storing & preserving
Best used right away — quality drops fast. Most keep best refrigerated; storage crops prefer a cool, dry spot.
- Freeze: Blanch briefly, cool, then freeze — keeps color and texture.
- Can: Pressure-can low-acid vegetables; water-bath only pickled/acidified ones.
General home-preservation guidance — for tested processing times and safety, follow the National Center for Home Food Preservation.
Growing timeline
Companion planting — with cited sources
From US/Canada cooperative-extension publications and peer-reviewed studies. Evidence-tier dots show how strongly each recommendation is backed: ●●● peer-reviewed mechanism · ●● extension consensus · ● traditional knowledge with a plausible mechanism.
Pairs well with (33)
- AniseEvidence tier C: Traditional practice with plausible mechanism but limited empirical replicationpredator-attract
Anise umbels supply nectar to parasitoid wasps and syrphids on the same model as dill and cilantro. Cited in extension insectary references though less commonly than dill.
Source: S13
- Apple MintEvidence tier C: Traditional practice with plausible mechanism but limited empirical replicationpest-deter
Shares the carvone/menthol volatile profile of spearmint; same brassica-deterrent guidance with the same caution to use containers because of aggressive rhizomes.
Source: University of Maryland Extension
- Bunching OnionEvidence tier C: Traditional practice with plausible mechanism but limited empirical replicationpest-deter
Scallions interplanted at row edges are cited by extension home-garden references as reducing cabbage aphid and (more modestly) cabbage maggot pressure on brassicas. Evidence is observational; results vary by site.
Source: University of Maryland Extension, S13
- CarawayEvidence tier C: Traditional practice with plausible mechanism but limited empirical replicationpredator-attract
Caraway is a biennial Apiaceae whose second-year flowering umbels supply nectar for parasitoid wasps and syrphids, like dill and cilantro. Cited in extension insectary references; effect is supplemental to other Apiaceae nectaries.
Timing: Useful only in year two when caraway flowers.
Source: S13
- CeleriacEvidence tier C: Traditional practice with plausible mechanism but limited empirical replicationpest-deter
Shares the Apium graveolens companion profile with common celery; see common celery for full discussion. Volatile-based partial deterrence of imported cabbageworm is reported but lightly replicated.
Source: University of Maryland Extension, S13
- CilantroEvidence tier C: Traditional practice with plausible mechanism but limited empirical replicationpredator-attract, pollinator-attract
Flowering cilantro is among the most-cited insectary plants in US extension materials for attracting syrphids, lacewings, and small parasitoid wasps that suppress cabbage aphid and cabbageworm.
- Common BeanEvidence tier C: Traditional practice with plausible mechanism but limited empirical replicationn-fixation
Beans provide modest in-place nitrogen contribution useful for heavy-feeding brassicas; extension home-garden guides recommend bush bean as a brassica neighbor for this reason. Effect on actual yield is modest in a single season.
Source: University of Maryland Extension
- Common BeetEvidence tier C: Traditional practice with plausible mechanism but limited empirical replicationsoil-conditioning
Beets are commonly recommended near brassicas; both are moderate to heavy feeders in similar fertility windows and beet leaves return potassium-rich residues.
Source: University of Maryland Extension
- Common CeleryEvidence tier C: Traditional practice with plausible mechanism but limited empirical replicationpest-deter
Celery is traditionally planted with cabbage and other brassicas; extension home-garden references propose that celery foliage volatiles (apiole, limonene) deter imported cabbageworm adults from laying. Empirical replication is limited but the pairing is consistently cited.
Source: University of Maryland Extension, S13
- Common ChivesEvidence tier C: Traditional practice with plausible mechanism but limited empirical replicationpest-deter, pollinator-attract
Chive volatiles share the masking effect of bulb onion; flowering chives also attract syrphids whose larvae prey on cabbage aphid colonies.
Source: University of Maryland Extension, S13
- Common HyssopEvidence tier C: Traditional practice with plausible mechanism but limited empirical replicationpest-deter, pollinator-attract
Hyssop is recommended in extension home-garden guides as a brassica-bed neighbor; its volatile oils plausibly confuse cabbage white butterflies (Pieris rapae) and the flowers attract parasitic wasps and bees. Direct field trials are limited.
Source: University of Maryland Extension
- Common LeekEvidence tier C: Traditional practice with plausible mechanism but limited empirical replicationpest-deter
Allium volatiles are frequently cited by extension as a partial deterrent to cabbage maggot (Delia radicum) and aphids on brassicas, though replicated yield trials are limited and effects are inconsistent. Leek's long season alongside the brassica crop makes it a convenient bed-mate.
Source: University of Maryland Extension, S13
- Common OnionEvidence tier C: Traditional practice with plausible mechanism but limited empirical replicationpest-deter
Onion sulfur volatiles are widely cited by US/Canada extension home-garden references as a partial deterrent for cabbage maggot (Delia radicum) and cabbage aphid (Brevicoryne brassicae). Replicated field trials are mixed but the practice is consistent and the rooting depths do not compete.
Source: S5, University of Maryland Extension, S13
- Common OreganoEvidence tier C: Traditional practice with plausible mechanism but limited empirical replicationpest-deter, pollinator-attract
Carvacrol- and thymol-rich oregano volatiles plausibly repel cabbage moth; the flowers strongly attract bees and small parasitoid wasps. Field replication is limited but the practice is widely supported in extension home-garden guides.
Source: Penn State Extension, University of Maryland Extension
- Common ParsleyEvidence tier C: Traditional practice with plausible mechanism but limited empirical replicationpredator-attract
Bolting parsley umbels feed parasitoids of cabbageworm and diamondback moth; supplemental to dill/cilantro insectary plantings.
Source: S13
- Common RosemaryEvidence tier C: Traditional practice with plausible mechanism but limited empirical replicationpest-deter, pollinator-attract
Rosemary volatiles (1,8-cineole, camphor) deter cabbage moth in choice tests; bed-edge planting is recommended by extension home-garden guides. Best where rosemary is hardy or grown in containers.
Region: Reliable perennial in zones 8+; grow as container in colder regions.
Source: Penn State Extension, University of Maryland Extension
- Common SageEvidence tier C: Traditional practice with plausible mechanism but limited empirical replicationpest-deter, pollinator-attract
Sage's thujone/camphor-rich oils have been shown in choice assays to deter cabbage moth (Pieris rapae) oviposition and to support parasitic wasps when in flower. Common bed-edge companion in extension home-garden guides.
Source: Penn State Extension, University of Maryland Extension
- Common ThymeEvidence tier C: Traditional practice with plausible mechanism but limited empirical replicationpest-deter, pollinator-attract
Thymol- and carvacrol-rich thyme volatiles have been shown in choice assays to deter cabbage moth (Pieris rapae) oviposition. Flowers attract bees and small parasitoid wasps. Recommended as a brassica-bed edge in extension home-garden guides.
Source: Penn State Extension, University of Maryland Extension
- Creeping RosemaryEvidence tier C: Traditional practice with plausible mechanism but limited empirical replicationpest-deter, pollinator-attract
Same volatile profile as upright rosemary; lower habit makes it well suited as a bed-edge groundcover near brassicas.
Source: University of Maryland Extension
- Creeping ThymeEvidence tier C: Traditional practice with plausible mechanism but limited empirical replicationpest-deter, pollinator-attract
Creeping thyme makes a useful living mulch at brassica-bed edges; thymol-rich oils plausibly deter cabbage moth and the flowers are heavily bee-visited.
Source: University of Maryland Extension
- Cultivated GarlicEvidence tier C: Traditional practice with plausible mechanism but limited empirical replicationpest-deter
Garlic volatiles are reported by extension guides to reduce cabbage aphid (Brevicoryne brassicae) colonization and to provide modest cabbage maggot deterrence when interplanted with cole crops. Field trial results are mixed.
Source: University of Maryland Extension, S13
- DillEvidence tier C: Traditional practice with plausible mechanism but limited empirical replicationpredator-attract, pollinator-attract
Flowering dill umbels provide accessible nectar and pollen for adult Cotesia glomerata, C. rubecula, and Diadegma insulare — key parasitoids of imported cabbageworm (Pieris rapae) and diamondback moth (Plutella xylostella). Multiple extension insectary references in US/Canada recommend dill specifically for brassica beds.
Timing: Allow some plants to flower mid-season to match peak caterpillar pressure.
Source: S1, S5, UMass Center for Agriculture
- English LavenderEvidence tier C: Traditional practice with plausible mechanism but limited empirical replicationpest-deter, pollinator-attract
Lavender's volatile terpenes (linalool, linalyl acetate) plausibly mask brassica crops from cabbage white butterflies; flowers strongly attract bees and parasitic wasps. Bed-edge planting is the extension recommendation.
Region: Best in well-drained beds, zones 5-9.
Source: Penn State Extension, University of Maryland Extension
- Garlic ChivesEvidence tier C: Traditional practice with plausible mechanism but limited empirical replicationpest-deter
Garlic chive volatiles are listed alongside other alliums for partial cabbage aphid suppression in extension companion-planting references.
Source: University of Maryland Extension
- Greek OreganoEvidence tier C: Traditional practice with plausible mechanism but limited empirical replicationpest-deter, pollinator-attract
Highest-carvacrol Origanum subspecies; same brassica-bed guidance as O. vulgare, with slightly stronger volatile profile.
Source: Penn State Extension, University of Maryland Extension
- LavandinEvidence tier C: Traditional practice with plausible mechanism but limited empirical replicationpest-deter, pollinator-attract
Lavandin (L. angustifolia × L. latifolia) shares English lavender's volatile profile and pollinator attractiveness; recommended for the same brassica-border use.
Source: University of Maryland Extension
- Leaf CeleryEvidence tier C: Traditional practice with plausible mechanism but limited empirical replicationpest-deter
Shares Apium graveolens chemistry and the same partial-deterrence rationale; see common celery for full discussion.
Source: University of Maryland Extension
- LovageEvidence tier C: Traditional practice with plausible mechanism but limited empirical replicationpredator-attract
Lovage is a long-lived perennial Apiaceae whose umbels supply nectar for parasitoid wasps and syrphids; extension insectary references include it among Apiaceae herbs that boost natural-enemy populations in vegetable gardens. Effect is supplemental to dill/cilantro nectaries.
Source: S13
- Mother Of ThymeEvidence tier C: Traditional practice with plausible mechanism but limited empirical replicationpest-deter, pollinator-attract
Low-growing thyme; same thymol-volatile rationale as T. vulgaris and T. praecox. Useful living-mulch border for brassicas.
Source: University of Maryland Extension
- ParsnipEvidence tier C: Traditional practice with plausible mechanism but limited empirical replicationpest-deter
Parsnip is occasionally cited as a brassica companion: long root depth doesn't compete, and bolting second-year parsnip umbels feed parasitoid wasps. Effect is supplemental.
Source: S13
- PeppermintEvidence tier C: Traditional practice with plausible mechanism but limited empirical replicationpest-deter
Peppermint volatiles (menthol, menthone) are the strongest of the Mentha species and are sometimes cited for cabbage moth and ant repellence. Container culture is mandatory near vegetable beds.
Source: Penn State Extension, University of Maryland Extension
- SpearmintEvidence tier C: Traditional practice with plausible mechanism but limited empirical replicationpest-deter
Mint volatiles (carvone, menthol) plausibly repel cabbage white butterflies and flea beetles; small-plot trials show modest reductions. Always plant mint in containers or sunken pots near brassica beds — never directly in the bed — because rhizomes are aggressive.
Source: Penn State Extension, University of Maryland Extension
- Sweet MarjoramEvidence tier C: Traditional practice with plausible mechanism but limited empirical replicationpest-deter, pollinator-attract
Sweet marjoram's terpene volatiles (terpinen-4-ol, sabinene) plausibly mask brassica volatiles from cabbage white butterflies; flowers attract parasitic wasps and hoverflies.
Source: University of Maryland Extension
Avoid planting near (9)
- Black WalnutEvidence tier B: Extension consensus across multiple US/Canada land-grant institutionsallelopathy-negative
Cabbage and several other brassicas are listed as juglone-sensitive in extension tolerance tables.
Source: Penn State Extension, S8
- Common RadishEvidence tier C: Traditional practice with plausible mechanism but limited empirical replicationalternate-host-pest
Radish is a brassica and shares clubroot, flea beetle, and cabbage aphid with cole crops. Extension references advise treating radish as part of the brassica rotation rather than interplanting freely with cabbage.
Source: University of Maryland Extension
- Common TomatoEvidence tier C: Traditional practice with plausible mechanism but limited empirical replicationnutrient-competition
Both crops are heavy feeders with overlapping calcium demand; extension home-garden references advise separating them to reduce competition that contributes to tomato blossom-end rot and brassica tip-burn. Cabbage-preferred slightly higher soil pH also conflicts with tomato preference. Mechanism is plausible but field-replicated evidence is modest.
Source: University of Maryland Extension, S13
- Common WormwoodEvidence tier C: Traditional practice with plausible mechanism but limited empirical replicationallelopathy-negative
Wormwood produces absinthin and related sesquiterpene lactones that leach from foliage and roots and have been shown to inhibit germination and growth of nearby vegetables. Extension sources advise siting it apart from vegetable beds.
Source: Penn State Extension, University of Maryland Extension
- Garden CressEvidence tier C: Traditional practice with plausible mechanism but limited empirical replicationalternate-host-pest
Brassicaceae; shares flea beetle and clubroot with cole crops. Extension references advise treating cresses as part of the brassica rotation rather than interplanting freely.
Source: University of Maryland Extension
- HorseradishEvidence tier C: Traditional practice with plausible mechanism but limited empirical replicationalternate-host-pest
Horseradish is a brassica and hosts the same pests (flea beetle, cabbage aphid) and clubroot (Plasmodiophora brassicae). Extension guides advise not interplanting or rotating horseradish with cole crops.
Source: University of Maryland Extension
- Sea KaleEvidence tier C: Traditional practice with plausible mechanism but limited empirical replicationalternate-host-pest
Perennial brassica that hosts cabbage maggot, flea beetle, and clubroot; extension references advise keeping sea kale in a dedicated bed away from annual cole crops to avoid concentrating pest and disease pressure.
Source: University of Maryland Extension
- StrawberryEvidence tier C: Traditional practice with plausible mechanism but limited empirical replicationflavor-folklore
Strawberry / brassica avoidance is commonly listed in folk companion charts but extension support is thin. Included with flavor-folklore tag because the claim is too widely repeated to silently omit.
Source: University of Maryland Extension
- Upland CressEvidence tier C: Traditional practice with plausible mechanism but limited empirical replicationalternate-host-pest
Brassicaceae; shares flea beetle, cabbage aphid, and clubroot susceptibility with cole crops. Extension references advise keeping cresses out of brassica beds and rotations to avoid concentrating pest and disease pressure.
Source: University of Maryland Extension
Trap crops for this plant (5)
- Common NasturtiumEvidence tier B: Extension consensus across multiple US/Canada land-grant institutionstrap-crop
Nasturtium concentrates cabbage aphid (Brevicoryne brassicae) and is preferred over cabbage by some cabbageworm and flea beetle adults; extension trap-crop guides recommend planting nasturtium border rows 2-3 weeks before transplanting brassicas so it is established as a sink during the vulnerable seedling stage. Avoid interplanting directly within the brassica row, which can create pest bridges.
Timing: Sow nasturtium 2-3 weeks before transplanting brassicas; remove or treat heavily infested trap-crop plants before aphids spill back.
Source: S1, UMass Center for Agriculture
- Mustard GreensEvidence tier B: Extension consensus across multiple US/Canada land-grant institutionstrap-crop
Glossy-leaved Brassica juncea (oriental / brown mustard) is the canonical extension-recommended flea-beetle trap crop on the perimeter of cole-crop fields. AAFC and US Prairie state extension trials show 50-80% concentration of flea beetle damage in the trap strip.
Timing: Establish trap strip 1-2 weeks before main crop emerges.
Region: Most useful in Prairie Canada and northern US.
Source: S1, S22, Agriculture and Agri-Food Canada
- Yellow RocketEvidence tier B: Extension consensus across multiple US/Canada land-grant institutionstrap-crop
Yellow rocket (Barbarea vulgaris) is a dead-end trap crop for diamondback moth — adults prefer it for oviposition but saponins prevent larval survival. Documented in Cornell and OMAFRA brassica IPM trials.
Region: Northeast US and Ontario.
Source: S1, University of Guelph / OMAFRA
- Black MustardEvidence tier C: Traditional practice with plausible mechanism but limited empirical replicationtrap-crop
Black mustard is occasionally used as a flea-beetle and harlequin-bug trap crop on edges of cabbage plantings; less commonly recommended than B. juncea but cited in southeastern US extension materials.
Region: Cited especially in the southeast US for harlequin bug (Murgantia histrionica) trapping.
Source: S11, NC State Extension
- Rat-Tailed RadishEvidence tier C: Traditional practice with plausible mechanism but limited empirical replicationtrap-crop
Like other radishes, rat-tailed radish can serve as a flea beetle and harlequin bug trap crop on brassica perimeters; see common radish for complete discussion.
Source: S11
Good successors in rotation (2)
- DaikonEvidence tier B: Extension consensus across multiple US/Canada land-grant institutionssoil-conditioning, biofumigation
Tillage radish (forage/oilseed daikon) is a standard fall cover crop preceding spring brassica plantings: deep taproot breaks compaction, captured nitrogen is released as residue decomposes, and glucosinolate residues provide modest biofumigation. See cover-crop notes for full details.
Timing: Sow August-September; winter-kill in zones 5-6 leaves a clean seedbed by spring.
Source: SARE, S29, Midwest Cover Crops Council
- Ethiopian MustardEvidence tier B: Extension consensus across multiple US/Canada land-grant institutionsbiofumigation
Brassica carinata is used as a high-glucosinolate biofumigant cover crop: incorporated residues release isothiocyanates (especially 2-propenyl-ITC) that suppress soil-borne pathogens (Verticillium, Sclerotinia) and some nematodes. See cover-crop entry for full discussion; on the receiving brassica crop the benefit is partly offset by clubroot concerns when used in tight rotation.
Timing: Incorporate at flowering for maximum ITC release; wait 2-3 weeks before transplanting susceptible crops.
Sources cited
- S1
- Cornell University Cooperative Extension — vegetable production guides
- S11
- University of Georgia Cooperative Extension
- S12
- NC State Extension
- S13
- University of New Hampshire Extension
- S15
- UMass Center for Agriculture (UMass Extension)
- S18
- SARE (Sustainable Agriculture Research and Education)
- S22
- University of Saskatchewan / Saskatchewan Ministry of Agriculture
- S23
- University of Guelph / OMAFRA (Ontario)
- S25
- Agriculture and Agri-Food Canada
- S29
- Cornell Soil Health Lab / Northeast Cover Crop Council (NECCC)
- S30
- Midwest Cover Crops Council (MCCC)
- S5
- Michigan State University Extension
- S6
- Penn State Extension
- S8
- Iowa State University Extension and Outreach
- S9
- University of Maryland Extension — Home & Garden Info Center
Care & troubleshooting— extension-sourced, with citations
When to feed, prune & water
Attract beneficial insects and protect pollinators
Protection- Routine carePlant insectary flowers and tolerate light pestsstrong evidence — extension confidence
Grow a diversity of flowering plants (including small-flowered umbels and asters) to feed predators and parasitoids, and tolerate low pest numbers so natural enemies have prey to stick around.
- Routine careNever spray open bloomsstrong evidence — extension confidence
Avoid insecticides on flowering plants and apply any needed sprays in the evening when pollinators aren't active, and favor selective products over broad-spectrum ones to spare bees and beneficials.
Feed brassicas while heading
Feeding- Routine careSide-dress nitrogen every 3-4 weeks· every 24 days · ~9 wksstrong evidence — extension confidence
Brassicas are heavy nitrogen feeders. Side-dress with a nitrogen-rich amendment every 3-4 weeks during active growth until heads/leaves near harvest size.
Mulch to suppress weeds and retain moisture
Mulch- Routine careApply organic mulch around plantsstrong evidence — extension confidence
Spread a few inches of straw, shredded leaves, or compost around established plants (keeping it off stems) to hold soil moisture, suppress weeds, and moderate soil temperature; wait until soil has warmed for heat-loving crops.
Plan crop rotation
Rotation- Routine careRotate plant families between bedsstrong evidence — extension confidence
Avoid planting the same family in the same bed in consecutive years (aim for a 3+ year gap), grouping crops by family so soilborne diseases and pests that build up don't carry over to the next susceptible crop.
- Routine careSequence for soil healthmoderate evidence — extension confidence
Follow heavy feeders like tomatoes and brassicas with legumes or a cover crop to support soil fertility and structure, and keep simple notes each year so you can track where each family grew.
Protect the garden from deer
Protection- Routine careFence the gardenstrong evidence — extension confidence
A fence about 8 feet tall and tight to the ground is the most reliable barrier; an outward-angled or double fence, or monofilament line strung at 30 to 36 inches, can also deter deer on smaller beds.
- Routine careRotate repellents as a supplement· every 2 wksmoderate evidence — extension confidence
Where fencing isn't feasible, apply odor/taste repellents and alternate formulations, reapplying every couple of weeks and after rain; combining repellents with fencing works best.
Protect the garden from rabbits and voles
Protection- Routine careFence out rabbitsstrong evidence — extension confidence
Surround beds with 1-inch mesh chicken wire at least 2 feet tall with the bottom buried or staked down a few inches so rabbits can't push under it.
- Routine careReduce vole habitat and guard stemsstrong evidence — extension confidence
Keep grass and mulch pulled back from plant bases and crowns to remove vole cover, mow surrounding vegetation, and use hardware-cloth guards around vulnerable woody stems before winter.
Buttoning (Broccoli/Cauliflower)
DisorderUnusual this time of year.
- CulturalUse young, well-hardened transplants and avoid cold stressstrong evidence — extension confidence
Set out vigorous, properly hardened-off transplants that have not become overgrown, and avoid transplanting into prolonged cold (roughly below 50F for many days), since cold and stress at this stage cause premature tiny heads.
- CulturalKeep plants growing steadilymoderate evidence — extension confidence
Maintain adequate fertility and moisture so plants grow without checks, since low fertility, drought, or other stress also trigger buttoning.
Clean up debris and sanitize at season end
SanitationUnusual this time of year.
- Routine careRemove spent plants and fallen debrisstrong evidence — extension confidence
Pull and clear old plants, dropped fruit, and leaf litter at season end, since many pests and diseases overwinter in this debris; dispose of diseased material rather than composting it.
- Routine careClean tools, stakes, and cagesmoderate evidence — extension confidence
Wash and sanitize stakes, cages, and tools that touched diseased plants before storing or reusing them to avoid carrying pathogens into next season.
Cutworm collars at transplant
ProtectionUnusual this time of year.
- Routine careSet a collar around each new transplantstrong evidence — extension confidence
When setting out transplants, slip a collar (a toilet-paper tube, paper cup with the bottom cut out, or similar) around each stem and press it a couple inches into the soil so it stands a few inches above ground, blocking cutworms from the stem.
Floating row cover timing
ProtectionUnusual this time of year.
- Routine careCover at planting and seal the edgesstrong evidence — extension confidence
Lay floating row cover over the crop right at seeding or transplanting and bury the edges with soil so pests can't get under; don't cover ground where the same crop grew last year, since overwintered pupae would emerge inside.
- Routine careRemove at flowering for pollinated cropsstrong evidence — extension confidence
On crops that need insect pollination, take the cover off once flowering begins so bees can reach the blooms; on self-pollinated or leafy crops you can leave it longer.
Harden off seedlings
ProtectionUnusual this time of year.
- Routine careGradually expose plants to the outdoors· every 1 days · ~2 wksstrong evidence — extension confidence
Starting about two weeks before transplanting, set seedlings outside in a sheltered, shady spot for a few hours and lengthen their time and sun exposure each day, avoiding windy days, to prevent transplant shock.
- Routine careEase back on water and transplant on a mild daystrong evidence — extension confidence
Water a little less during hardening (without letting plants wilt) to toughen growth, then transplant in late afternoon or on a cool, cloudy, calm day.
Something looks wrong?
Describe what you see on your purple yu choy sumand we'll rank the likely causes — most likely first, least-invasive fix first.
Bacterial soft rot
Diseasesevere- CulturalRemove rotting plants and produce (manage, not cure)strong evidence — extension confidence
Soft rot can't be cured once tissue breaks down; promptly remove and discard affected plants and produce so the bacteria don't spread to neighbors or other stored vegetables.
- CulturalAvoid wounds and excess moisturestrong evidence — extension confidence
Harvest in dry conditions, handle gently to avoid bruising, control insects that create entry wounds, and improve drainage; cure and store bulbs and roots cool and dry.
- CulturalDon't overwater and rotatemoderate evidence — extension confidence
Avoid waterlogged soil and overhead watering that splashes bacteria, and rotate away from previously affected fleshy crops to lower disease pressure.
Black rot (brassicas)
Diseasesevere- CulturalRemove plants; rotate; use clean seedstrong evidence — extension confidence
A bacterial disease with no cure. Pull infected plants, rotate brassicas 2-3 years, use hot-water-treated or certified seed, and avoid working plants when wet.
Clubroot
Diseasesevere- CulturalRotate widely and raise soil pHstrong evidence — extension confidence
A soilborne disease that persists for years. Avoid brassicas in that bed for 5-7 years, improve drainage, and liming toward pH 7.2 suppresses it.
White mold (Sclerotinia stem rot)
Diseasesevere- CulturalRemove infected plants (manage, not cure)strong evidence — extension confidence
There's no cure for an infected plant; cut out and bag affected plants including the black sclerotia, and don't compost them, since sclerotia survive years in soil.
- CulturalOpen the canopy and rotatestrong evidence — extension confidence
Space plants widely, control weeds, orient rows to prevailing wind, and avoid overhead watering at bloom to dry the canopy; rotate to non-host crops (corn or other grasses) for several years.
- CulturalWater at the base, not overheadmoderate evidence — extension confidence
Use drip or soaker irrigation to keep foliage and the soil surface drier, which discourages the sclerotia germination and mycelial growth that drive white mold.
Alternaria Leaf Spot / Head Rot (Brassicas)
Diseasemoderate- CulturalUse clean seed, rotate, and bury debrisstrong evidence — extension confidence
Plant certified clean seed, rotate about 3 years away from brassicas, and remove or bury crop debris since lower-leaf lesions seed infection of heads.
- CulturalAvoid excess nitrogen and improve airflowmoderate evidence — extension confidence
Avoid over-fertilizing with nitrogen and space plants for good airflow, since dense, lush canopies and high humidity worsen the disease.
- ChemicalApply fungicide preventively, rotating FRAC groups· every 1 wkstrong evidence — extension confidence
Apply fungicide before disease establishes and rotate among different FRAC groups (e.g., groups 7, 3, and 9) per the label for resistance management.
Cabbage aphid
Pestmoderate- CulturalKnock off colonies and remove debris· every 4 daysmoderate evidence — extension confidence
Rinse colonies off with a strong water spray and pull badly infested leaves; clear old brassica debris and weedy mustards that carry the aphid over.
- OrganicApply a labeled insecticidal soap· every 1 wk · ~3 wksmoderate evidence — extension confidence
Apply a labeled insecticidal soap per the label with thorough coverage of undersides and growing tips; add a spreader so it doesn't bead off waxy leaves, and use a lower rate to avoid leaf burn.
Cabbage white & looper caterpillars
Pestmoderate- CulturalHand-pick + insect netting· every 3 days · ~3 wksstrong evidence — extension confidence
Pick caterpillars by hand and cover plants with insect netting to block egg-laying butterflies.
- OrganicBt (Bacillus thuringiensis) - label use only· every 1 wk · ~3 wksmoderate evidence — extension confidence
Spray Bt var. kurstaki on leaf undersides per label; reapply after rain. Spares pollinators.
Damping-off (seedlings)
Diseasemoderate- CulturalDry out, ventilate, sow into clean mixstrong evidence — extension confidence
Use sterile seed-starting mix, bottom-water and let the surface dry between waterings, add airflow, and don't over-sow. Damping-off can't be cured once a seedling collapses.
Diamondback Moth (Brassicas)
Pestmoderate- CulturalScout, use row cover, and conserve natural enemiesstrong evidence — extension confidence
Scout undersides of leaves, exclude moths with floating row cover on young plants, and conserve parasitoid wasps that control this pest.
- OrganicTarget young larvae and rotate modes of action· every 1 wkstrong evidence — extension confidence
Treat small larvae with Bt (B. thuringiensis) or a spinosyn product, and rotate classes every application per the label, since diamondback moth readily develops insecticide resistance.
Downy Mildew (Brassicas)
Diseasemoderate- CulturalImprove airflow and manage seedling moisturestrong evidence — extension confidence
Space plants, improve air circulation, and irrigate early in the day, since cool nights with high humidity, fog, or dew favor this oomycete, especially in seedling beds.
- CulturalRotate and use resistant varietiesstrong evidence — extension confidence
Rotate at least 2 years away from brassicas and choose downy-mildew-resistant varieties where available, recognizing resistance varies with local pathogen strains.
- ChemicalApply fungicide preventively in seedling/transplant stage· every 1 wkmoderate evidence — extension confidence
Protect transplants and young crops with an oomycete-active fungicide preventively, rotating modes of action per the label.
Harlequin bug
Pestmoderate- CulturalSanitation and exclusionstrong evidence — extension confidence
Destroy old cole crops and weedy mustards that serve as breeding sites, clean up debris in early spring before populations build, and use insect netting or row cover over young brassicas.
- CulturalHand-pick bugs and eggs· every 3 daysstrong evidence — extension confidence
Pick adults, nymphs, and the distinctive striped egg rows into soapy water; consistent removal early in the season keeps small plantings ahead of this pest.
- OrganicTreat nymphs if needed· every 1 wkmoderate evidence — extension confidence
If nymphs are abundant, a spinosad product can help per the label; essential-oil products have tested poorly, so rely mainly on sanitation, netting, and hand-picking.
Slugs & snails
Pestmoderate- CulturalTrap, hand-pick at night, reduce cover· every 2 days · ~3 wksstrong evidence — extension confidence
Pick at night with a flashlight, set shallow beer traps, water in the morning so soil dries by dusk, and clear damp hiding spots.
- OrganicIron-phosphate bait - label use only· every 1 wk · ~3 wksmoderate evidence — extension confidence
Scatter a labeled iron-phosphate slug bait sparingly per the label; it's pet- and wildlife-safer than metaldehyde.
Stink bugs (brown marmorated and native)
Pestmoderate- CulturalExclude with row cover and clear nearby weedsstrong evidence — extension confidence
Cover susceptible crops with floating row cover before bugs arrive, and remove weeds and groundcover near the garden in early spring where stink bugs feed before moving to crops. Lift covers on flowering crops that need pollination.
- CulturalHand-pick bugs and egg masses· every 3 daysstrong evidence — extension confidence
Scout in the morning and drop adults, nymphs, and egg clusters into a bucket of soapy water; regular hand-picking keeps low populations in check since most garden insecticides work poorly on adults.
- OrganicSpot-treat young nymphs if numbers climb· every 1 wkmoderate evidence — extension confidence
If small nymphs are abundant, a botanical such as pyrethrin or azadirachtin, or insecticidal oil, may give some suppression per the label; adults are largely unaffected, so rely mainly on exclusion and hand-picking.
Tarnished plant bug / lygus
Pestmoderate- CulturalManage surrounding weedsstrong evidence — extension confidence
Keep broadleaf weeds mowed or removed around the garden, since lygus build up on flowering weeds and move to crops as those weeds dry down; avoid mowing large weedy areas right beside fruiting crops at bloom.
- CulturalVacuum or shake plants to monitor and reduce· every 5 daysmoderate evidence — extension confidence
Tap plants over a light-colored tray to check for nymphs; a handheld vacuum used once or twice weekly can hold low to moderate numbers down on small plantings.
- OrganicTreat nymphs if damage is building· every 1 wkmoderate evidence — extension confidence
For active nymph infestations, azadirachtin or a Beauveria bassiana product can give some control per the label; preserve the parasitic wasps and other natural enemies that help suppress lygus.
White Rust (Brassicas/Crucifers)
Diseasemoderate- CulturalControl cruciferous weeds and rotatestrong evidence — extension confidence
Remove wild mustard and other cruciferous weeds, rotate about 3 years away from crucifers, and bury infected debris by deep tillage, since the pathogen survives on debris and weed hosts.
- CulturalAvoid overhead irrigationstrong evidence — extension confidence
Use drip irrigation and space for drying, since prolonged leaf wetness drives this oomycete disease.
Whiteflies
Pestmoderate- CulturalRemove infested leaves and hose off· every 4 daysmoderate evidence — extension confidence
Pick off and discard heavily infested lower leaves and rinse colonies off undersides with a strong spray of water; yellow sticky cards help monitor numbers.
- OrganicApply a labeled soap or oil· every 1 wk · ~3 wksmoderate evidence — extension confidence
Apply a labeled insecticidal soap or neem oil per the label, covering leaf undersides; these reduce but won't eliminate whiteflies, so repeat as needed.
Cabbage & onion root maggots
PestmoderateUnusual this time of year.
- CulturalCover at planting with floating row coverstrong evidence — extension confidence
Place floating row cover over the crop at seeding or transplanting and bury the edges so flies cannot lay eggs at the stem base; do not use if the same crop grew there last year, since trapped pupae would hatch underneath.
- CulturalRotate and delay plantingstrong evidence — extension confidence
Rotate susceptible crops to a new spot each year and, where possible, delay planting to late spring to miss the main egg-laying window.
Cutworms
PestmoderateUnusual this time of year.
- CulturalPlace stem collars on transplantsstrong evidence — extension confidence
Push a collar (cardboard tube, can, or cup with bottom removed) a couple inches into the soil around each stem so it extends a few inches above ground; this blocks cutworms from reaching the stem.
- CulturalScout soil and hand-remove· every 3 days · ~2 wksstrong evidence — extension confidence
In the evening or early morning, check the soil around damaged plants and remove curled larvae by hand; tilling beds about two weeks before planting also reduces larvae and pupae.
- OrganicApply a labeled Bt or spinosad· every 1 wk · ~3 wksmoderate evidence — extension confidence
If damage continues, apply a labeled Bacillus thuringiensis (kurstaki) or spinosad product per the label, targeting small larvae; Bt works best on young first- and second-instar cutworms.
Flea beetles
PestmoderateUnusual this time of year.
- CulturalRow cover seedlingsstrong evidence — extension confidence
Float insect netting over seedlings until they're large enough to outgrow damage; remove for flowering crops needing pollination.
- OrganicSpinosad or kaolin clay - label use only· every 1 wk · ~2 wksmoderate evidence — extension confidence
For heavy pressure on seedlings, a labeled spinosad or kaolin-clay product helps. Follow the label.
Aphids
Pestlow- CulturalBlast off with water· every 3 days · ~2 wksstrong evidence — extension confidence
Knock colonies off with a strong jet of water in the morning; repeat every few days. Light infestations rarely need more.
- OrganicInsecticidal soap - label use only· every 1 wk · ~3 wksmoderate evidence — extension confidence
For persistent colonies apply insecticidal soap to undersides per label. Avoid open flowers.
Bolting (premature flowering)
Disorderlow- CulturalShade and harvest before boltingstrong evidence — extension confidence
Once a plant bolts it can't be reversed, so harvest at the first sign of stalk formation; 30-50% shade cloth and steady watering during heat help delay bolting in cool-season crops.
- CulturalUse bolt-resistant varieties and succession sowmoderate evidence — extension confidence
Choose heat-tolerant, slow-bolt varieties and stagger small sowings so a heat spell doesn't take out the whole planting.
Earwigs
Pestlow- CulturalTrap and remove· every 1 days · ~2 wksstrong evidence — extension confidence
Set rolled damp newspaper, low tuna-style cans of oil, or short tubes near plants at dusk, then dump trapped earwigs into soapy water each morning; reduce mulch and damp hiding spots near vulnerable seedlings.
- OrganicApply a bait only if damage persists· every 1 wkmoderate evidence — extension confidence
Established plants usually tolerate earwigs, which also eat aphids; if seedlings are being destroyed, a spinosad-based bait labeled for earwigs can help per the label.
Edema (oedema)
Disorderlow- CulturalBalance watering and humiditystrong evidence — extension confidence
Edema comes from the plant taking up more water than it releases, not a pathogen, so water less often and water in the morning so roots aren't taking up water faster than leaves transpire on cool, humid days.
- CulturalImprove airflow and drainagestrong evidence — extension confidence
Space plants for good air movement, improve soil and container drainage, and avoid overcrowding under cover; affected leaves won't recover but new growth comes in normally once conditions balance.
Lettuce & cabbage tipburn
Disorderlow- CulturalKeep moisture even and ease off nitrogenstrong evidence — extension confidence
Tipburn is a transient calcium issue driven by water stress, not low soil calcium, so water steadily to avoid dry-wet cycles and don't over-apply nitrogen, which competes with calcium uptake.
- CulturalChoose tolerant varieties and harvest on timemoderate evidence — extension confidence
Pick tipburn-tolerant varieties and harvest heads promptly during hot spells rather than letting them sit and grow rapidly.
Nitrogen deficiency
Deficiencylow- CulturalFeed with balanced fertilizer· every 2 wks · ~4 wksstrong evidence — extension confidence
Apply a balanced organic fertilizer or fish emulsion; new growth greens up within ~2 weeks. Don't overcorrect.
Transplant shock
DisorderlowUnusual this time of year.
- CulturalWater in well and provide shade· every 1 days · ~1 wksstrong evidence — extension confidence
Water transplants in thoroughly at planting and keep the root zone evenly moist for the first week or two, and provide temporary shade during hot, sunny, or windy spells to reduce stress while roots establish.
- CulturalHarden off and plant gently next timestrong evidence — extension confidence
Most plants recover on their own; to prevent recurrence, harden off seedlings before planting, set them out in mild weather or evening, and avoid disturbing the roots when transplanting.