How to Grow Obsidian Tomato

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Obsidian Tomato

Solanum lycopersicum 'Obsidian'

vegetable

Obsidian is a striking indeterminate heirloom tomato variety prized for its deep purple-black coloring and rich, complex flavor. The fruits are medium-sized (3-4 oz), round, and develop a distinctive dark mahogany to nearly black hue as they mature. This variety combines exceptional taste with ornamental appeal, making it popular among gardeners seeking unique, flavorful tomatoes.

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Example Obsidian Tomato timeline · Pittsburgh, PA (Zone 6b)

Plant Obsidian Tomato
Around Apr 17

Near Pittsburgh's average last spring frost.
Tend & protect
Late spring–summer

Watering, feeding, and pest-watch reminders.
Harvest Obsidian Tomato
Around Jul 1

≈ 75 days after planting

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

Growing Conditions

☀️

Sun: Full sun, 8+ hours daily (minimum 6 hours)

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Water: Consistent moisture (1-2 inches weekly); water deeply at soil level to avoid foliage diseases; avoid overhead watering; more critical during fruiting

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Spacing: 24-36 inches

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Days to maturity: 75-85

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Planting depth: Seed: 0.25 inches deep; Transplant: bury stem up to first true leaves

Soil

Type: Rich, well-draining loamy soil with organic matter

pH: 6.0-6.8

Amendments:

Compost aged manure peat moss or coconut coir slow-release fertilizer

Growing Zones

Find your zone →

Zones 5-10; can be grown in zones 3-4 with season extension

3a 3b 4a 4b 5a 5b 6a 6b 7a 7b 8a 8b 9a 9b 10a 10b

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Growth Stages

Seedling

2-3 weeks

Tiny seedlings emerge with cotyledons (seed leaves), followed by true leaves. Plants are delicate and pale green.

Maintain 75-80°F soil temperature; provide bright grow lights 14-16 hours daily; keep soil consistently moist but not waterlogged; thin crowded seedlings

Vegetative Growth

4-6 weeks

Young transplants develop true leaves and strong stems; plants grow vigorously with alternating leaf clusters. Foliage is medium to dark green.

Harden off seedlings before transplanting outdoors; space 24-36 inches apart; support with stakes or cages early; remove lower leaves as plant grows to improve airflow

Flowering

3-4 weeks

Small yellow flowers appear in clusters (trusses) along the main stem and branches. Flowers are about 0.5 inches across.

Maintain consistent watering to prevent blossom end rot and flower drop; provide balanced or slightly higher phosphorus fertilizer; ensure good air circulation; avoid excessive nitrogen which promotes foliage at expense of flowers

Fruiting

5-6 weeks

Small green fruits develop and enlarge over 4-6 weeks. As maturity approaches, fruits gradually transition from green to dark purple-mahogany to nearly black at full ripeness.

Maintain consistent deep watering (1-2 inches weekly); apply mulch to regulate soil moisture and temperature; continue supporting heavy fruit clusters; remove some leaf cover to allow light penetration if needed; fertilize every 2-3 weeks with balanced formula

Harvest

8-12 weeks (ongoing until frost)

Mature fruits are dark purple-black, slightly soft when gently squeezed, and fully flavorful. The plant continues producing until frost.

Harvest when fully colored and slightly soft; pick in morning for best flavor; handle carefully as dark fruits may show blemishes easily; indeterminate plants will continue flowering and fruiting until frost

Companion Planting

Plan your garden →

Plant with:

Basil Parsley Marigold Borage Carrot Onion Chives Nasturtium

Avoid planting near:

Brassicas (cabbage, broccoli, cauliflower) Fennel Dill Walnut trees

Common Pests

Hand-pick daily, encourage parasitic wasps, use Bacillus thuringiensis (Bt), neem oil spray
Spray with neem oil or insecticidal soap, use yellow sticky traps, introduce parasitic wasps
Increase humidity and air circulation, spray with water, use neem oil or sulfur dust
Remove infected lower leaves, improve air circulation, mulch to prevent soil splash, avoid overhead watering, apply copper fungicide
Remove infected foliage promptly, improve air circulation, apply copper or chlorothalonil fungicide, avoid overhead watering
Use disease-resistant varieties, practice crop rotation, remove infected plants, sterilize tools

Uses

🍳

Slicing & Fresh Eating

Culinary

Obsidian tomatoes are exceptional for slicing due to their deep, complex flavor profile with subtle sweet and smoky notes. They make stunning salads both visually and culinarily, and are prized by chefs for their unique color and refined taste. [source]

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Sauces & Cooking

Culinary

The dark pigmentation and dense fruit make Obsidian excellent for homemade sauces, salsas, and cooked tomato dishes. Their bold flavor deepens when cooked, creating rich, nuanced sauces. [source]

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Ornamental & Display

Household

The striking dark purple-black fruits on green foliage make Obsidian tomatoes highly ornamental. They serve as attractive edible landscaping and make beautiful garnishes for dishes. [source]

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Antioxidant Content

Medicinal

Dark-pigmented tomato varieties like Obsidian contain elevated levels of anthocyanins and lycopene, potent antioxidants that may support cardiovascular health and reduce inflammation. [source]

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Seed Saving

Craft

As an heirloom open-pollinated variety, Obsidian tomatoes are ideal for seed saving. Gardeners can collect seeds from mature fruits and preserve the variety year to year. [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 dark purple-black and slightly yield to gentle pressure; pick in morning when flavor is most concentrated; Obsidian tomatoes can be harvested at the breaker stage (first color change) and ripened indoors; fruits continue ripening after picking; remove entire truss once most fruits are ripe; continue harvesting until first frost; typical yield is 10-20 lbs per mature plant

Fun Facts

🌱 Obsidian tomatoes get their deep purple-black color from high concentrations of anthocyanins, the same antioxidant pigments found in blueberries, blackberries, and red wine.
🌱 The color darkens as tomatoes mature and benefit from full sun exposure; fruits grown in partial shade may remain more purple than black, as the dark pigmentation requires significant UV light exposure.
🌱 Obsidian is an indeterminate variety, meaning it grows continuously and produces fruit until frost, potentially yielding 10+ pounds per plant over a season in ideal conditions.

Gardening Terms

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

Full Sun Heirloom Mulch pH Transplant True Leaves

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