How to Grow Cambridge Blue
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Cambridge Blue
Brassica oleracea var. capitata f. rubra
vegetableCambridge Blue is a red/purple cabbage variety known for its dense, compact heads and deep blue-purple coloring. This heirloom variety was developed at Cambridge University and produces solid, medium-sized heads with excellent flavor and storage capacity. It's prized for both culinary use and its ornamental appearance in the garden.
When should you plant Cambridge Blue in your zone?
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Example Cambridge Blue timeline · Pittsburgh, PA (Zone 6b)
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Plant Cambridge Blue
Around Apr 17Near Pittsburgh's average last spring frost.
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Tend & protect
Late spring–summerWatering, feeding, and pest-watch reminders.
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Harvest Cambridge Blue
Around Jul 16≈ 90 days after planting
Sample dates for Pittsburgh, PA. Sign up to get exact Cambridge Blue dates for your own zip code.
Growing Conditions
Soil
Growing Zones
Find your zone →Thrives in zones 3-9; prefers cooler weather, particularly suited to zones 4-8
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Get my Cambridge Blue timeline →Growth Stages
Seedling
2-3 weeksTiny seed leaves emerge; true leaves develop with characteristic cabbage texture. Plant is 1-2 inches tall.
Keep soil moist, maintain bright light (grow lights if indoors), maintain 60-70°F. Thin seedlings to prevent crowding.
Vegetative Growth
3-4 weeksPlant develops 6-8 true leaves; begins establishing root system. Leaves are blue-purple, initially looser before heading begins.
Transplant outdoors when 4-6 weeks old and 4-6 inches tall. Harden off gradually. Space 18 inches apart. Keep soil consistently moist.
Head Formation
4-6 weeksOuter leaves tighten around forming center head. Plant appears more compact; head is initially loose then gradually becomes denser.
Maintain consistent watering and nutrient availability. Feed with balanced fertilizer every 3-4 weeks. Remove any yellow or damaged outer leaves.
Head Maturation
3-4 weeksCompact, solid head forms with deep purple-blue color. Head feels firm and dense when squeezed gently. Leaves wrap tightly around head.
Continue regular watering and monitor for pests. Head is ready when it reaches desired size (4-6 inches diameter) and feels solid. Do not let heads split.
Harvest Ready
Continuous harvest window over 2-3 weeksHead is fully mature, dense, and solid with characteristic deep blue-purple color throughout. Outer wrapper leaves are turgid.
Harvest before temperatures drop to freezing or heads may crack. Cut head at base with sharp knife. Can be stored for weeks in cool conditions.
Companion Planting
Plan your garden →Plant with:
Avoid planting near:
Common Pests
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Row covers on young plants, hand-pick caterpillars, spray with Bacillus thuringiensis (Bt), neem oil
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Bacillus thuringiensis (Bt), spinosad, neem oil, encourage parasitic wasps
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Row covers, diatomaceous earth, neem oil, kaolin clay spray
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Yellow sticky traps, reflective mulch, neem oil, insecticidal soap
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Crop rotation (3-year minimum), lime application, remove infected plants, avoid planting in affected soil
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Use disease-resistant varieties, remove infected leaves, improve air circulation, avoid overhead watering
Uses
Fresh salads and slaws
CulinaryRaw purple cabbage adds vibrant color and a slightly sweet, mild flavor to salads and slaws. The anthocyanin pigments create a striking visual presentation while providing nutritional benefits. [source]
Fermented and pickled dishes
CulinaryCambridge Blue's firm texture makes it ideal for fermentation into sauerkraut and kimchi, and for pickling. The extended storage life allows preservation of the harvest. [source]
Nutritional and anti-inflammatory support
MedicinalRich in vitamins C and K, sulfur compounds, and anthocyanins that support digestive health and provide antioxidant benefits. Traditional use in promoting joint and digestive health. [source]
Natural dye production
HouseholdThe blue-purple pigment (anthocyanin) can be extracted and used as a natural dye for fabrics and paper crafts. pH changes cause color shifts from pink to blue. [source]
Ornamental garden display
CraftThe deep purple-blue color and compact form make Cambridge Blue an attractive addition to ornamental vegetable gardens and edible landscapes. Often grown as much for beauty as for food. [source]
This is not medical advice. LizPlants is not a medical resource. Always consult a qualified healthcare professional before using plants medicinally.
Harvest Tips
Harvest when heads are firm and solid, typically 90-120 days after transplanting. Cut the head at the base with a sharp knife, leaving the stem and outer leaves on the plant. Check for firmness by applying gentle pressure—a mature head will feel solid and dense. Harvest before the first hard freeze or heads may crack. Cambridge Blue stores exceptionally well in a cool root cellar or refrigerator (32-40°F, 90% humidity) for up to 5 months.
Fun Facts
- 🌱 Cambridge Blue was developed at Cambridge University in England and is an heirloom variety that has been cultivated since at least the 1800s, maintaining its reputation for reliability and storage quality.
- 🌱 The purple-blue color comes from anthocyanin pigments that intensify in cool weather, making fall-grown Cambridge Blue darker and more vibrant than spring-grown specimens.
- 🌱 A single Cambridge Blue plant can be harvested multiple times—if you leave the stem and roots in place after cutting the main head, smaller secondary heads will form below.
Gardening Terms
New to gardening? Learn about terms used in this guide:
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