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How to Grow Karl the Great Tomato

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Karl the Great Tomato

Solanum lycopersicum 'Karl the Great'

vegetable

Karl the Great is a determinate heirloom tomato variety known for producing large, meaty fruits with excellent flavor. This German heritage tomato bears deep red fruits weighing 10-16 ounces, perfect for slicing and fresh eating. The plants are compact and productive, making them ideal for both garden beds and containers.

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Example Karl the Great Tomato timeline · Pittsburgh, PA (Zone 6b)

  1. Plant Karl the Great Tomato

    Around Apr 17

    Near Pittsburgh's average last spring frost.

  2. Tend & protect

    Late spring–summer

    Watering, feeding, and pest-watch reminders.

  3. Harvest Karl the Great Tomato

    Around Jun 21

    ≈ 65 days after planting

Sample dates for Pittsburgh, PA. Sign up to get exact Karl the Great Tomato dates for your own zip code.

Growing Conditions

☀️
Sun: Full sun, 6-8 hours daily minimum, preferably 8+ hours
💧
Water: Consistent moisture; water deeply 1-2 inches per week. Keep soil evenly moist but not waterlogged. Drip irrigation or soaker hoses are ideal to prevent fungal diseases. Avoid wetting foliage.
📏
Spacing: 24 inches
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Days to maturity: 65-80 days from transplant
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Planting depth: 0.25 inches for seeds; transplants should be buried deeper (up to first true leaves)

Soil

Type: Rich, well-draining loamy soil with good organic matter
pH: 6.0-6.8
Amendments:
Compost Aged manure Bone meal Balanced organic fertilizer Calcium (crushed eggshells or gypsum to prevent blossom end rot)

Growing Zones

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Thrives in zones 5-8, can be grown as annual in zones 3-9

3b 4a 4b 5a 5b 6a 6b 7a 7b 8a 8b 9a

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Growth Stages

1

Seedling

4-6 weeks

Tiny plants with cotyledons (seed leaves) emerge within 5-10 days. True leaves appear within 1-2 weeks.

Provide bright light (grow lights 3-4 inches above seedlings). Keep soil moist but not waterlogged. Maintain 70-75°F temperature. Thin seedlings to strongest plant per cell.

2

Vegetative Growth

3-4 weeks after transplanting

Plant develops sturdy stems and multiple sets of leaflets. Compact, bushy growth pattern with no flowers yet. Plant reaches 12-18 inches tall.

Harden off transplants gradually over 7-10 days before planting outdoors. Plant in warm soil (60°F minimum, ideally 65-70°F). Pinch off lower leaves once established. Support with stakes or cages early.

3

Flowering

2-3 weeks

Yellow flowers appear in clusters (trusses). Flowers are self-fertile and will set fruit readily. Plant continues compact, determinate growth.

Maintain consistent watering to prevent flower drop. Avoid excess nitrogen which reduces flowering. Provide calcium to prevent blossom end rot. Light pruning of lower leaves improves air circulation.

4

Fruiting

3-4 weeks

Marble-sized green fruits develop at flower clusters. Fruits grow rapidly and begin color change from green to red. Multiple trusses develop simultaneously on determinate plants.

Maintain steady water supply—critical during fruit development. Apply mulch to regulate soil moisture and temperature. Remove yellowing lower leaves to improve air flow. Support heavily laden branches.

5

Harvest

3-6 weeks of continuous harvest

Fruits reach full deep red color, feel slightly soft when gently squeezed, and are 10-16 ounces. Peak flavor and ripeness achieved.

Harvest when fully red and slightly soft. Pick fruits regularly to encourage continued production. Can harvest breaker stage fruits (first blush of color) and ripen indoors if needed. Season ends with first frost.

Companion Planting

Plan your garden →

Plant with:

Basil Parsley Marigold Borage Carrot Onion Garlic Nasturtium Marigold

Avoid planting near:

Fennel Dill Cabbage Broccoli Potato Corn Brassicas

Common Pests

  • Hand-pick large caterpillars; use Bacillus thuringiensis (Bt); encourage natural predators like parasitic wasps; row covers on young plants

  • Spray with neem oil; increase humidity; strong water spray to dislodge; insecticidal soap; maintain plant health

  • Yellow sticky traps; neem oil; insecticidal soap; reflective mulch; encourage beneficial insects

  • Remove infected lower leaves; improve air circulation; water at soil level only; mulch; copper fungicide if needed; resistant variety selection

  • Remove infected leaves immediately; improve air flow; avoid overhead watering; copper or sulfur fungicide; crop rotation

  • Maintain consistent moisture; add calcium (eggshells, gypsum); mulch; avoid excessive nitrogen; proper watering schedule

Uses

🍳

Slicing and Fresh Eating

Culinary

Karl the Great's large, meaty fruits are perfect for slicing fresh into sandwiches, salads, and plates. The excellent balance of sweetness and acidity makes them ideal for eating raw without processing. [source]

🍳

Sauce and Preservation

Culinary

The dense flesh and rich flavor make Karl the Great excellent for making fresh tomato sauces, salsas, and pastes. Can be canned, frozen, or dried for long-term storage. [source]

💊

Nutritional and Cardiovascular Health

Medicinal

Heirloom tomatoes like Karl the Great are rich in lycopene and other antioxidants associated with heart health and disease prevention. Contains vitamin C, potassium, and folate. [source]

🏠

Garden Productivity

Household

As a determinate variety, Karl the Great produces a concentrated harvest ideal for batch cooking and preserving, making efficient use of garden space and time. [source]

🎨

Heirloom Seed Saving

Craft

Karl the Great is an open-pollinated heirloom variety that breeds true, allowing gardeners to save seeds year after year, preserving this German heritage variety. [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 fruits are fully red and slightly soft to the touch, typically 65-80 days after transplanting. Karl the Great is determinate (bush type) and produces most fruit within 3-4 week window. Pick regularly to encourage continuous production. Fruits can be harvested at 'breaker stage' (first blush of color) and ripened indoors in cool conditions. For maximum flavor, allow fruits to fully ripen on the vine. Harvest before first frost; pick remaining green fruits and ripen indoors.

Fun Facts

  • 🌱 Karl the Great is named after Charlemagne (Karl in German), the founder of the Holy Roman Empire, reflecting its status as a traditional German heirloom variety prized for centuries in European gardens.
  • 🌱 As a determinate (bush-type) tomato, Karl the Great produces its entire crop within 3-4 weeks rather than continuously throughout the season—perfect for gardeners wanting to harvest and preserve in bulk.
  • 🌱 This variety was nearly lost to history but has been revived by heirloom seed savers and specialty seed companies, making it a living connection to agricultural heritage and traditional European gardening practices.

Gardening Terms

New to gardening? Learn about terms used in this guide:

Full Sun Heirloom Mulch Transplant True Leaves
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