Cruciferous vegetables – broccoli, cauliflower, kohlrabi, cabbage

Cole Crops – Broccoli, Cauliflower, Kohlrabi, Cabbage

Cole crops (brassicas, Brassicaceae) rank among the most nutritious plants you can grow in your garden. Broccoli, cauliflower, kohlrabi, curly kale, Brussels sprouts and cabbage all belong to a single species Brassica oleracea, differing only in which part of the plant we harvest: dense florets (broccoli, cauliflower), swollen stem (kohlrabi), leaves (cabbage, kale) or small leaf buds (Brussels sprouts). While cole crops are more demanding in terms of nutrients and care than most vegetables, the reward is a bountiful harvest full of vitamins, fiber and bioactive compounds – sulforaphane and indole-3-carbinol with proven anti-cancer effects.

Common Reference Table – Quick Overview

1. Broccoli (Brassica oleracea var. italica)

Broccoli is a nutritional powerhouse of the garden – it contains sulforaphane with anti-cancer properties, vitamins C and K, folate and fiber. Although it ranks among the more demanding vegetables, even less experienced gardeners can succeed with it if they follow basic principles.

Varieties

• Early: Marathon F1, Batavia F1, Fiesta F1. Reliable varieties with large, compact main heads, suitable for spring cultivation.
• Late: Ironman F1, Belstar F1. Longer growing season, but after harvesting the main head they abundantly produce side shoots.
• Broccoli raab (cima di rapa): Italian type – instead of a compact head, small shoots with buds are harvested. Fast growth and distinctly different, mildly bitter taste.
• Purple Sprouting: Overwintering type – plant in summer, harvest the following spring. Excellent frost tolerance and provides fresh greens in spring earlier than most other varieties.

Pre-Growing

Broccoli is almost always pre-grown – direct sowing in the bed is unreliable, plants lag behind and are more vulnerable to pests.

Spring cultivation (most common approach):
1. Sow from mid-February into trays or multipots. Depth: 1 cm. Germination temperature: 18–22 °C.
2. Germination: 5–7 days.
3. Prick out into 8–10 cm pots immediately after cotyledons develop.
4. Hardening off: 7–10 days before planting, gradually accustom seedlings to outdoor temperatures – first in shade, then in direct sun.
5. Outdoor planting: April–May, after the last hard frosts. Spacing: 40–50 cm.

Fall cultivation:
Sow in June, plant in July. Harvest occurs in September and October. Fall broccoli is often higher quality than spring – cool nights slow head formation, pest pressure is lower and flavor is more pronounced.

Care

• Watering: Regular and generous, especially during head formation. Lack of water causes buds to open prematurely and heads to remain small. Roughly 25–30 l/m2 per week, more in hot weather.
• Fertilizing: Broccoli is a heavy nutrient consumer. The foundation is well-rotted compost worked in before planting, supplemented with 2–3 fertilizing applications of nitrogen and potassium-rich fertilizer during the season.
• Mulching: A layer of mulch 5–8 cm maintains soil moisture and prevents overheating of the root zone – broccoli poorly tolerates sustained heat.

Harvest

• Main head: Harvest when buds are dense, compact and firm, but not yet beginning to open into yellow flowers. Cut with 10–15 cm of stem – the stem is also edible and tasty.
• Side shoots: Most varieties continue producing smaller side shoots after the main head is harvested. Continuous harvesting can extend the season by 4–8 weeks.
• Don't wait – once buds begin to open and yellow flowers appear, broccoli rapidly loses flavor and nutritional value.

2. Cauliflower (Brassica oleracea var. botrytis)

Cauliflower is notorious among cole crops for its demanding nature – any stress during growth (drought, heat above 25 °C, temporary chilling, nutrient deficiency) will result in deformed, small or prematurely flowering heads. On the other hand, it rewards you with delicate flavor and culinary versatility.

Varieties

• White classics: Erfurt, Igloo, Boris F1. Firm white heads requiring blanching by covering with leaves.
• Green romanesco: Romanesco Natalino. Geometrically perfect fractal spirals, more delicate and nutty flavor. Better tolerates mild stress than white varieties.
• Purple: Graffiti F1, Di Sicilia Violetto. Attractive purple color – striking raw, color fades after cooking. No blanching needed.
• Orange: Cheddar F1. Natural orange color comes from high beta-carotene content. Blanching is also unnecessary.

Pre-Growing and Planting

The procedure is identical to broccoli, but with stricter requirements for stable conditions:

1. Sow: February–March for spring cultivation, June for fall.
2. Key warning: Cauliflower does not tolerate interrupted growth. Substrate drying, chilling or nutrient deficit at any stage will cause formation of small, underdeveloped "buttons" instead of full heads.
3. Outdoor planting: April–May. Spacing: 50–60 cm – cauliflower needs more space than broccoli to fully develop.

Blanching Heads

White varieties require blanching – without protection from sun, the head yellows, becomes bitter and loses its delicate texture.

Procedure:
1. Once the head reaches the size of a tennis ball, fold or tie the outer leaves over it.
2. The leaves form a natural shelter protecting from sun and rain. In cool, cloudy weather, checking every two days is sufficient.
3. Purple, green and orange varieties do not require blanching – their color is a natural characteristic and is not harmed by sun.

Care

• Watering: Absolutely critical. Cauliflower needs balanced soil moisture without significant fluctuations – even short drought in the critical growth phase damages head quality. Roughly 30–40 l/m2 per week, daily in dry conditions.
• Fertilizing: Highest nutrient requirements of all cole crops. Compost + 3–4 fertilizing applications per season. Specific problem: boron deficiency causes hollow, brown-discolored heads – preventively apply borax at 1 g/m2 or leaf fertilizer containing boron.
• Mulching: Essential for maintaining even moisture and cooling the root zone.

Harvest

• Harvest when the head is firm, compact and has full color according to variety. Overripe cauliflower loosens, falls apart into separate segments and flowers.
• Cut with 2–3 protective leaves, which protect the head during handling and storage.

3. Kohlrabi (Brassica oleracea var. gongylodes)

Kohlrabi is the fastest and most forgiving cole crop – from planting to harvest only 50–70 days pass. The edible part is the swollen stem (not the root), which is excellent raw in salads as well as cooked.

Varieties

• White (green): Luna, Lannro, Konan F1. Delicate flavor, fast growth, ideal for spring cultivation.
• Blue (purple): Blankyt, Violeta, Azur Star. Slightly thicker skin, but significantly better storability.
• Giant: Superschmelz – grows exceptionally over 5 kg while maintaining crisp, non-woody flesh. A curiosity that works.

Pre-Growing and Planting

1. Sow into trays: from March for spring harvest, June–July for fall cultivation.
2. Sowing depth: 1 cm. Germination: 5–10 days.
3. Outdoor planting: from April. Spacing: 25–30 cm.
4. Kohlrabi is excellent for successive planting – sow new seedlings at three-week intervals and get continuous harvest from spring to fall.
5. Kohlrabi seedlings are usually available in garden centers from April.

Care

• Watering: Regular and even – irregular watering causes bulbs to become woody and crack. Particularly critical during hot, dry periods.
• Fertilizing: Medium requirements. Compost worked in before planting supplemented with light fertilizing during growth usually suffices.
• Mulching: Helps maintain even moisture, which determines harvest quality.

Harvest

• Harvest at diameter 6–8 cm for white varieties and 8–10 cm for blue ones. Overgrown kohlrabi loses tenderness and becomes woody – with the exception of Superschmelz, which maintains quality even at large size.
• Cut just above ground. Remove leaves immediately after harvest – a bulb without greens keeps in the refrigerator for 2–3 weeks.

4. Brussels Sprouts (Brassica oleracea var. gemmifera)

Brussels sprouts is the marathon of cole crops – growing season lasts 120–180 days, but after the first fall frosts it offers sweet, nutty sprouts with no competition. Frost activates conversion of starches to sugars and significantly improves flavor.

Varieties

• Early: Jade Cross F1, Franklin F1. Harvest from September, suitable for regions with shorter fall.
• Late: Long Island Improved, Diablo F1. Harvest from November, excellent frost tolerance – in favorable winters can remain in the garden until February.
• Red: Red Bull F1, Falstaff. Purple sprouts with decorative effect and pronounced flavor.

Pre-Growing and Planting

1. Sow: March–April. Depth: 1 cm. Germination temperature: 15–20 °C.
2. Outdoor planting: May. Spacing: 50–60 cm – plants grow 60–100 cm tall and need space for air circulation.
3. Plant deep (up to the first true leaves) and hill up soil around the stem during summer to ensure stability of tall plants.

Care

• Watering: Regular throughout the season from May planting until November and beyond harvest.
• Fertilizing: High requirements. Compost worked in before planting and 2–3 fertilizing applications, especially potassium-rich fertilizer that supports sprout formation and firmness.
• Support: Tall plants are prone to being blown over in strong wind – stake them early in summer.
• Removing lower leaves: In September and October, gradually remove yellowing lower leaves. This improves air circulation, reduces risk of fungal diseases and accelerates sprout ripening.

Harvest

• Sprouts ripen from bottom to top. Harvest by breaking off once they reach 2–3 cm diameter and are firm to the touch.
• After the first fall frosts, sprouts are noticeably sweeter – the same effect as with curly kale.
• Harvest period ranges from September/October to January or February depending on variety and weather course.

5. Main Pests and Diseases of Cole Crops

Cole crops share the same range of pests and diseases, so protective measures can be applied broadly across the entire group.

Cabbage White Butterfly and Rape White Butterfly

Butterflies lay eggs on leaf undersides. Caterpillars then chew leaves down to bare skeleton – on untreated beds they can destroy entire crop.

Solutions:
1. Mesh or non-woven fabric – the most reliable and completely mechanical protection. Apply immediately after planting. Maximum mesh size 7 mm.
2. Bacillus thuringiensis (BT) – biological product acting exclusively on caterpillars, completely harmless to pollinators and other animals. Spray every 7–10 days during the growing season.
3. Hand picking: Regularly check leaf undersides and collect yellow eggs and caterpillars.
4. Plant protection products – use only as a last resort when biological methods are insufficient for severe infestation.

Flea Beetles

Small black beetles (1–3 mm) chew small holes in leaves. Particularly attack young seedlings and kohlrabi, which in extreme cases can die. Population explodes in hot, dry weather.

Solution: Non-woven fabric as physical barrier, regular watering (flea beetles prefer dry conditions), dusting with wood ash or diatomaceous earth as supplementary measure.

Cabbage Aphid

Tiny white flies lodged on leaf undersides suck plant sap and excrete honeydew, on which sooty mold settles. Colonization of weak plants significantly slows growth.

Solution: Yellow sticky traps for monitoring and population reduction, potassium soap spray, supporting natural predators – ladybugs and lacewings.

Clubroot (Plasmodiophora brassicae)

The most serious disease of the entire cole crop group – roots swell and deform into characteristic "tumors," plants progressively wilt and die. The pathogen survives in soil 15–20 years without a host, no cure exists.

Prevention is the only effective strategy:
1. Crop rotation: Do not grow brassicas on the same bed sooner than 5–7 years.
2. Liming: The pathogen thrives in acidic soil. Apply agricultural lime and maintain pH above 7.0 – at higher pH disease spread is significantly limited.
3. Healthy seedlings: Buy seedlings exclusively from verified suppliers, never transfer soil from infested beds.
4. Drainage: The pathogen spreads with stagnant water – waterlogged beds are highly risky.
5. Resistant varieties: Modern F1 hybrids such as Clapton F1 (cauliflower) or Kilaton F1 (cabbage) have partial genetic resistance.

Gray Mold and Bacterial Rots

Affect particularly cauliflower and broccoli in wet and cool weather. Prevention includes adequate spacing for air circulation, watering at the roots (not on foliage) and immediate removal of affected plant parts.

6. Nutrition of Cole Crops – Detailed Overview

Cole crops rank among the most nutrient-demanding vegetables. Insufficient fertilizing results in small, poor quality harvest, premature flowering and increased disease susceptibility.

Fertilizing Plan

Micronutrients

• Boron: Deficiency causes hollow, brown-discolored heads in cauliflower, stem browning in broccoli. Apply borax (1 g/m2) or leaf fertilizer containing boron as preventive measure, especially on light soils.
• Molybdenum: Deficiency shows as "whip tail" – leaves curl and become narrow. Occurs mainly in acidic soils; regular liming reliably prevents it.

7. Cole Crop Growing Calendar for Central Europe

8. Frequently Asked Questions (FAQ)

Why is my broccoli flowering instead of forming heads?
The cause is stress – drought, sustained heat above 26 °C, nutrient deficiency or planting seedlings without prior hardening off. Broccoli responds to any stress by premature flowering as a survival mechanism. Ensure consistent watering, regular fertilizing and shade plants during tropical heat.

Why are my cauliflower heads small and deformed?
The cause is interrupted growth – substrate drying, chilling young seedlings or nutrient deficiency. Cauliflower is the most sensitive cole crop. Maintain constant moisture, fertilize regularly and don't plant too early in spring when night frosts threaten.

How can I most reliably prevent cabbage worm caterpillars?
The most effective is mesh netting with holes up to 7 mm laid over the bed immediately after planting. If caterpillars are already present, use Bacillus thuringiensis (biological product) or hand-pick caterpillars and eggs daily.

What is clubroot and how do I get rid of it?
This is a fungal disease caused by Plasmodiophora brassicae that deforms roots into characteristic tumors. No cure exists for infected plants or soil. Prevention: crop rotation with minimum 7-year break, liming to pH 7.0 and above, buying healthy seedlings and ensuring bed drainage.

Can I grow kohlrabi in a container?
Yes – kohlrabi is one of the few cole crops directly suited to container growing. Container at least 20 cm deep, quality potting soil, regular watering and 20–25 cm spacing. In containers it's advisable to choose compact white varieties.

Why aren't my Brussels sprouts forming sprouts?
Common causes: too late planting (plant by May at latest), potassium deficiency in the critical period or spacing too close. Brussels sprouts requires 120–180 days of growth and spacing of at least 50–60 cm.

What is the best preceding crop for cole crops?
Legumes (peas, beans) – they leave soil nitrogen reserves that cole crops use excellently. Other suitable preceding crops are cucumbers, tomatoes or onion vegetables. Never plant cole crops after each other or after rapeseed.

Can I grow different cole crop types side by side?
Technically yes, but all share the same pests and diseases. If clubroot attacks or heavy butterfly moth presence occurs, problems easily spread across the entire cole crop block. It's better to scatter individual types across different garden areas.

9. Tips for Beginners

1. Start with kohlrabi – it's the fastest and most forgiving of the entire group. From planting to harvest in 50–70 days, tolerates even minor growing mistakes.
2. Broccoli is significantly easier than cauliflower – produces side shoots even after main head harvest and better tolerates weather fluctuations and watering variations.
3. Mesh netting is essential, not a luxury – without physical protection against cabbage butterflies, you lose the essence of the harvest.