Choy sum

Care Guide: Planting, Soil & Watering

Overview: Choy sum is a fast, cool-season Asian brassica that grows best in full sun (or light shade where it is warm) and rich, moisture-retentive soil. The source calls for a slightly acidic, heavier soil kept steadily moist, since heat and dryness quickly turn the leaves bitter.

Quick Care Requirements

Requirement	Ideal Condition
Planting Season	Cool season – autumn-winter in frost-free areas, spring in temperate climates
Growth Rate	Fast
Soil Type	Rich, moisture-retentive (heavier) soil high in organic matter
Soil pH	Slightly acidic (just below neutral)
Water Need	Moderate to high – keep the soil consistently moist

Planting & Establishment

• Best Planting Season: These prize cool weather – in warm spells the leaves turn bitter and the plants bolt. In frost-free areas grow them through autumn and winter; in temperate climates plant in spring (and autumn), avoiding midsummer heat.
• How to Plant:
  • Hole Preparation: For transplants, make a hole a little wider than the root ball; for direct sowing, rake the bed to a fine, crumbly tilth and thin seedlings so each plant has room to develop.
  • Soil Amendments: Dig in plenty of well-rotted compost or organic matter before planting – leafy brassicas are hungry feeders that reward fertile, humus-rich ground.
  • Planting Depth: Set seedlings at the same depth they grew in the tray (cabbages can go a touch deeper, up to the first true leaves) and firm gently around them without burying the growing point.
• Growth Speed & Expectations: It grows fast when cool and well fed, reaching harvest in a matter of weeks; keep it moving with steady moisture and fertile soil.

Soil, Watering & Drainage Care

• Soil Mix & Drainage Needs: These prefer a heavier, moisture-retentive but still well-draining soil enriched with organic matter; avoid ground that stays waterlogged. In containers use a quality moisture-holding potting mix.
• Watering Schedule & Technique:
  • Young / Newly Planted: Water in well at planting and keep the bed consistently moist while seedlings establish – never let them wilt.
  • Established: Water deeply and evenly – any check from heat or dryness makes the leaves turn bitter and the plant bolt, so keep the soil reliably moist.
  • Seasonal Adjustments: Water more in warm, dry spells and ease back in cool, wet weather; a layer of mulch helps hold moisture in the soil.

Growing in Pots, Balconies & Indoors

choy sum is a cool-season leafy crop that thrives in pots, troughs and window boxes, which makes it a natural choice for a balcony or patio. The grower does not rate it as a true indoor houseplant, but a bright, sunny windowsill will still give you tender baby leaves and cut-and-come-again pickings.

Quick Details

• Container Size: A wide trough or pot at least about 20 cm (8 in) deep; grow several plants close together
• Indoor Suitability: Not a deep-room houseplant; a bright, sunny sill gives baby leaves and repeat cuttings
• Best Spot: full sun in cool climates, part shade where summers are hot – a bright balcony or patio
• Soil & Drainage: Rich, aerated organic mix (peat or coir with perlite or vermiculite); free-draining yet moisture-retentive
• Watering in Pots: Keep evenly moist – pots dry fast and brassica leaves turn tough and bitter if they dry out; never waterlogged

Indoors & On the Windowsill

• Houseplant limits: The grower lists choy sum as not suited to indoors; deep in a room the light is too weak for healthy, well-flavoured leaves.
• Windowsill growing: On a bright, sunny sill it earns its place as a cut-and-come-again crop – sow thickly, pick young leaves, and resow for a steady supply.
• Overwintering: As a hardy cool-season plant it shrugs off light frost outdoors; in a hard winter, shelter a pot in a cold porch or unheated greenhouse rather than a warm room, which is too dim.

On a Balcony or Patio

• Light & wind: Give it the brightest spot, but a little afternoon shade in hot weather helps stop it bolting. Walls and railings throw back heat and wind dries pots quickly, so check moisture daily in warm spells.
• Practicalities: A broad trough or several plants sharing a large planter works well; make sure surplus water can drain clear of the balcony floor.

Choosing the Pot, Soil & Long-Term Care

• Pot & drainage: A wide container about 20 cm deep with strong drainage holes; skip a standing-water saucer to avoid root rot. Terracotta breathes and dries faster, while glazed or plastic holds moisture longer – handy for a thirsty leaf crop.
• Potting mix: A rich, well-aerated organic mix – peat or coir with perlite or vermiculite – holds the steady moisture these greens like.
• Feeding: Potted greens use up their mix quickly and nutrients leach out with watering, so feed more often than plants in the ground, with a balanced, nitrogen-leaning liquid feed for lush leaves.
• Between crops: These are fast, short-lived croppers – refresh or replace the spent mix between sowings rather than nursing old plants along.

Bloom & Edible Flower Guide

Quick Details

• Bloom Season: Spring to summer
• Time to First Bloom: In its first season — choy sum is grown specifically for its flowering stems, which appear quickly as the plant runs up to bloom
• Flower Appearance: Small four-petalled yellow flowers on slender upright stems
• Edibility: Edible — the flowering stems, buds and open flowers are all eaten, lightly cooked, with a sweet, mild mustard flavor

Detailed Blooming Overview

Choy sum, whose name means “flowering heart,” is grown to be picked in bloom. The tender stems, topped with a few just-opening yellow cruciform flowers, are the whole point of the crop and are gathered when the first flowers show.

Flower Characteristics

• Small four-petalled (cruciform) yellow flowers on slender racemes.
• Both the buds and open flowers are eaten along with the stem.

Bloom Care & Thinning

• Harvesting the bloom: You can thin, but there is no need to — the flowers and stem are the harvest. Cut the stems as the first flowers open, which also prompts more shoots.
• Pollination: Pollinated by bees and also capable of self-pollination.

Bloom Health & Protection

• Cabbage aphids: Grey-green aphids often cluster on flowering shoots and buds; a strong jet of water, insecticidal soap or neem oil keeps them in check.
• Cabbage white caterpillars: These can graze buds and open flowers — a Bacillus thuringiensis (Bt) spray is a targeted, low-impact option.

Pruning, Training & Seasonal Maintenance

Choy sum is grown for its slender flowering stems with their tender buds and leaves, so — unlike the heading cabbages — bolting is the crop, not a fault. Harvest is a cut-and-come-again operation: cut the main flowering stem above a leaf node while the buds are still tight or just showing yellow, and side shoots follow for repeated picking. Beyond that, only dead or infected leaves are removed; there is no structural pruning.

Quick Pruning & Maintenance Specs

Pruning Tolerance	Low — harvest cuts drive side shoots; no shaping
Primary Pruning Window	When flowering stems form, buds tight to just opening
Typical Frequency	Main-stem cut, then repeated side-shoot cuts
Main Objective	Tender flowering stems and buds; drive further shoots
Young Plant Priority	Grow on fast; remove only damaged leaves
Mature Plant Priority	Cut flowering stems in time; harvest side shoots
Best Tool Type	Precision snips or a sharp knife
Avoid Heavy Pruning During	Heat spells, which make leaves bitter and coarse

Pruning by Plant Age & Size

Newly Established

Remove only dead or damaged leaves; let this quick crop grow away without check.

Young / Formative

No structural training. Grow it on until the flowering stems begin to rise from the leafy base.

Mature / Established

Cut the main flowering stem about 12 cm long, above a leaf node, while the buds are tight or barely open. Lower nodes then push side shoots, which are cut in turn over the following weeks.

Seasonal Pruning Schedule

Flowering-Stem Harvest

Objective — tender stems and buds. Remove — the main flowering stem above a node. Do NOT remove — the lower leaves and nodes that drive side shoots. Response — side shoots form for repeated cutting.

Ongoing Sanitary

Strip dead or infected leaves and check for Pieris and Spodoptera caterpillars, slugs and aphids in the leaf axils.

Special Growth to Remove

The deliberate cut is the flowering stem itself, taken above a node so side shoots break below it. Remove yellowing lower leaves, but keep healthy foliage, which fuels the side-shoot flush. The buds, flowers and stems are all edible together.

Container & Small-Space Pruning

Choy sum crops well in pots, and repeated flowering-stem cuts keep it compact and productive. In warm weather give light shade, since heat coarsens the leaves and shortens the picking window.

Tools

Precision snips or a sharp knife cut the tender stems cleanly above a node. No woody-pruning tools apply.

Tool Hygiene & Disease Risk

Increased risk — repeated cuts on a soft brassica leave many wounds, and the group carries soft rot and black rot. Keep the blade clean and sharp and disinfect it after cutting a diseased plant or between plants in an outbreak.

Cut Placement & Technique

Cut just above a healthy leaf node so the axillary buds there can break into a side shoot. A clean cut on the juicy hollow stem avoids crushing and rot.

Heavy Pruning & Rejuvenation

The repeated harvest cutting is the plant’s whole productive cycle — there is no separate hard rejuvenation. Once the plant is spent or heat-stressed, side-shoot production fades and it is cleared.

Post-Pruning Care

Water and lightly feed after the main-stem cut to support side shoots, and keep the plant cool and evenly moist to hold leaf and stem quality through repeated pickings.

Common Pruning Mistakes

• Cutting below the leaf nodes, leaving nothing to drive side shoots.
• Letting stems grow old and stringy before cutting, or harvesting in heat when they turn bitter.
• Stripping the healthy leaves the side-shoot flush depends on.

When NOT to Prune

Avoid harvesting hard in a heat spell or drought check, which coarsens the leaves and stems, and do not cut into a young plant before it has formed its flowering stems.

Recommended Tools (by task)

• precision_snips — clean cuts of flowering stems and side shoots just above a node.
• blade_disinfectant — cleaning the blade between plants when soft rot or black rot is present.

Pests, Diseases & Troubleshooting

Overview: Choy sum is a member of the cabbage family (Brassicaceae), so it shares the classic brassica pest and disease complex: leaf-chewing caterpillars, sap-sucking aphids, flea beetles and soil-borne root problems. The most reliable defence is cultural: rotate brassicas onto fresh ground each cycle, cover young plants with fine insect mesh from day one, keep plants unstressed and evenly watered, and clear crop debris promptly. Reach for sprays only after barriers and hand-picking.

Quick Troubleshooting Overview

Issue / Pest	Main Symptom	Primary Solution
Cabbage white caterpillars	Ragged holes in leaves, green/velvety caterpillars, dark frass	Insect mesh; hand-pick; spray Bt (Bacillus thuringiensis)
Cabbage aphid	Grey waxy colonies in leaf hearts, distorted growth	Blast off, encourage lacewings/ladybirds; insecticidal soap
Flea beetles	Tiny round ‘shot-hole’ pits in leaves, worst on seedlings	Mesh, keep soil moist, sticky traps; neem on heavy attack
Cabbage root fly	Wilting, blue-tinged foliage, maggots tunnelling the roots	Collars around stems, mesh barrier, crop rotation
Clubroot	Stunting, wilting in heat, swollen distorted roots	Lime to pH 7+, long rotation, remove & bin infected roots
Downy mildew	Yellow leaf blotches with grey mould beneath	Airflow, avoid wet foliage; copper if persistent

Common Pests & Management

• Cabbage white caterpillars (Pieris rapae & Pieris brassicae):
  • Symptoms: Velvety green (small white) or yellow-and-black hairy (large white) caterpillars chew large ragged holes and leave wet green-brown droppings in the leaf hearts. Clusters of yellow eggs sit on leaf undersides.
  • Prevention & Control: Cover plants with fine insect mesh from transplanting so egg-laying moths never reach them. Squash egg clusters and hand-pick caterpillars weekly. For heavy pressure spray Bacillus thuringiensis (Bt) or spinosad onto the caterpillars in the evening; encourage parasitic wasps by leaving flowering herbs nearby.
• Diamondback moth (Plutella xylostella):
  • Symptoms: Small, slender pale-green caterpillars that wriggle backwards when touched and graze the leaf underside, leaving thin ‘windowpane’ patches and small holes. Tiny grey moths flutter up when plants are disturbed.
  • Prevention & Control: Mesh exclusion and rotation. This pest resists many products, so rely on Bt/spinosad rotated with different modes of action, and protect the natural parasitoid wasps that keep it in check.
• Cabbage aphid (Brevicoryne brassicae):
  • Symptoms: Dense grey-green mealy, waxy colonies packed into growing points, leaf hearts and (on sprouts) inside the buttons; causes curling, stunting and sooty mould. Distinct from generalist green peach aphid by its powdery coating.
  • Prevention & Control: Inspect hearts regularly and dislodge early colonies with a water jet. Encourage ladybirds, hoverflies and lacewings. Spray insecticidal soap or neem, aiming into the leaf folds where they hide; remove badly infested outer leaves before they seed new colonies.
• Flea beetles (Phyllotreta spp.):
  • Symptoms: Tiny black (sometimes striped) beetles that jump when disturbed and pepper leaves with round ‘shot-hole’ pits; seedlings and thin-leaved mustards/mizuna can be shredded and checked badly.
  • Prevention & Control: Cover seedbeds with mesh, keep soil consistently moist (beetles prefer dry stressed plants), and use yellow sticky traps. A brassica-safe neem drench helps in severe outbreaks; grow past the vulnerable seedling stage under cover.
• Cabbage root fly (Delia radicum):
  • Symptoms: White maggots tunnel into the roots and stem base; plants wilt in warm spells, take on a blue-grey cast and may topple. Seedlings and transplants are most at risk.
  • Prevention & Control: Fit 12-15 cm cardboard or felt collars snug around each stem at planting to stop eggs reaching the soil, or grow under mesh. Rotate away from last season’s brassica ground and firm the soil around crowns.
• Cabbage looper & leaf miners (Trichoplusia ni):
  • Symptoms: Loopers are smooth green caterpillars that arch their bodies as they crawl and chew large holes; leaf-mining flies scribble pale tunnels through thin leafy-brassica foliage.
  • Prevention & Control: Hand-pick loopers and treat with Bt/spinosad as for cabbage whites. Remove mined leaves, keep mesh in place, and clear weeds that host both pests between crops.

Diseases & Fungal Issues

• Clubroot (Plasmodiophora brassicae):
  • Symptoms: Plants wilt in the heat of the day yet recover overnight, grow slowly and stay stunted; lifting reveals swollen, distorted, club-like galls on the roots. The soil-borne spores persist for many years.
  • Treatment & Management: There is no cure once soil is infested, so prevent: rotate brassicas on the longest cycle you can, raise soil pH to 7.0+ with lime, improve drainage, and never move infected soil or roots. Choose resistant cultivars where clubroot is known, and remove and bin (do not compost) affected roots.
• Downy mildew (Hyaloperonospora brassicae):
  • Symptoms: Angular yellow blotches on the upper leaf with a fluffy grey-white mould on the underside, worst in cool damp weather and on crowded seedlings; badly hit leaves brown and die.
  • Treatment & Management: Space plants for airflow, water at the base and keep foliage dry, and thin crowded seedlings. Remove infected leaves. Copper-based fungicide can protect new growth under persistent pressure.
• Black rot (Xanthomonas campestris pv. campestris):
  • Symptoms: Yellow V-shaped lesions spreading inward from the leaf margins, with blackened veins; the bacterium can rot heads and spread on seed and in warm wet weather.
  • Treatment & Management: Use clean, hot-water-treated or certified seed, rotate for at least three years, avoid working among wet plants, and remove infected plants promptly. No spray cures it, so sanitation and resistant varieties are key.
• Alternaria leaf spot (Alternaria brassicae / A. brassicicola):
  • Symptoms: Dark brown circular spots with concentric ‘target’ rings, often ringed by a yellow halo, on leaves and (in seed crops) pods; spots may drop out to leave holes.
  • Treatment & Management: Rotate, clear debris, and keep foliage dry with base watering and good spacing. Remove spotted lower leaves; a protectant copper or biofungicide helps in wet spells.

Growing Difficulties & Abiotic Problems

• Bolting:
  • Cause & Symptoms: Plants run to a flower stalk instead of forming a head or staying leafy, triggered by heat, long days, drought or transplant shock; leaves turn bitter.
  • Correction Strategy: Sow at the right season for your climate, keep water and nutrients steady, avoid root disturbance at transplanting, and choose bolt-resistant cultivars for warm spells. Harvest promptly once mature.
• Nutrient shortfalls:
  • Cause & Symptoms: Overall pale yellowing from the oldest leaves signals nitrogen shortage; purpling can indicate phosphorus lockout in cold soil. Brassicas are hungry, heavy feeders.
  • Correction Strategy: Enrich soil with compost before planting and side-dress leafy and heading types with a balanced or nitrogen-rich feed during active growth; warm soil before planting to ease phosphorus uptake.

What Helps — Products & Tools

For choy sum the core toolkit is fine insect mesh / floating row cover, stem collars against root fly, yellow sticky traps, and hand-picking. Biological and low-toxicity sprays cover the rest: Bacillus thuringiensis (Bt) or spinosad for caterpillars, insecticidal soap or neem oil for aphids, flea beetles and whitefly, and a copper-based fungicide for downy mildew and leaf spots. Lime corrects clubroot-prone acid soil. Always spray in the evening to protect pollinators and follow the label.

Propagation Guide

Choy sum is grown from seed, usually direct-sown, and needs no vegetative propagation; warmth makes it bolt and turn bitter, so it is grown in cool weather. The site records it as pollinated by bees and also self-pollinating, and while B. rapa is generally outcrossing, many choy sum are partly self-compatible — isolate plantings from other B. rapa greens if you want seed to come true. Fast and easy from seed.

Quick Propagation Specs

Best Propagation Method	Seed, usually direct-sown
Propagation Difficulty	Easy
Seed True-to-Type	Outcrossing species — crosses freely with other B. rapa greens, so isolate for true seed; F1 hybrids not true from saved seed
Best Propagation Season	Cool weather — autumn to spring in temperate zones, autumn and winter in frost-free areas (heat causes bolting and bitterness)
Seed Germination Time	Fast, often 3–7 days
Germination Temperature	Optimum around 20–25°C (68–77°F); germinates from about 7°C (45°F) upward
Seed Sowing Depth	About 1 cm (0.5 in)

Growing from Seed

Seed Handling & Viability

Brassica rapa seed keeps for several years stored cool and dry and needs no pre-treatment before sowing.

Sowing Season

Sow in the cool part of the year as the site advises; heat and root disturbance both trigger premature bolting and bitterness.

Sowing Depth & Thinning

Sow about 1 cm (0.5 in) deep where the plants are to grow, then thin seedlings — heading types need the most room, while cut-and-come-again leaves can stay closer.

Germination Conditions & Time

Keep evenly moist; germination is quick, often within 3–7 days.

Seedling Care

Sow in place where possible; if transplanting, move plants very small and only in cool weather, and keep them steadily moist to avoid a bolting check.