How to Grow Kauai Blue

Wikimedia Commons

Kauai Blue

Solanum lycopersicum 'Kauai Blue'

vegetable

Kauai Blue is an indeterminate heirloom tomato variety producing medium-sized fruits with a distinctive blue-purple coloration and rich, complex flavor. The dark pigmentation comes from anthocyanins, giving it both visual appeal and potential health benefits. This Hawaiian cultivar is prized by gardeners seeking unique colors and exceptional taste.

When should you plant Kauai Blue in your zone?

Get a personalized planting timeline — when to start seeds, transplant, and harvest — based on your USDA zone and local frost dates. Free to start.

Get my Kauai Blue timeline →

Example Kauai Blue timeline · Pittsburgh, PA (Zone 6b)

Plant Kauai Blue
Around Apr 17

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

Watering, feeding, and pest-watch reminders.
Harvest Kauai Blue
Around Jul 1

≈ 75 days after planting

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

Growing Conditions

☀️

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

💧

Water: Consistent, deep watering 1-2 inches per week; more during hot periods. Water at soil level to avoid foliar diseases. Maintain even moisture; avoid drought stress followed by heavy watering which causes fruit cracking.

📏

Spacing: 24 inches

📅

Days to maturity: 75-85 days from transplant to first ripe fruit

🌱

Planting depth: ¼ inch for seeds; bury transplants up to first true leaf set, as tomatoes root along buried stems

Soil

Type: Well-draining, fertile loamy soil rich in organic matter

pH: 6.0-6.8

Amendments:

Compost Aged manure Peat moss or coconut coir Bone meal for phosphorus Kelp meal for trace minerals

Growing Zones

Find your zone →

Thrives in zones 5-10; can grow in zone 3-4 with season extension techniques

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

Get my Kauai Blue timeline →

Growth Stages

Seedling

3-4 weeks

Small plant with 2-4 true leaves, 2-4 weeks old, delicate and pale green

Provide bright light (grow lights 3-4 inches above leaves), keep soil moist but not waterlogged, maintain 65-75°F, thin to strongest seedling if direct seeding

Vegetative/Transplant

2-3 weeks after planting

6-12 inch tall plant with 8+ true leaves, developing strong stem and branching

Harden off transplants over 7-10 days before planting outdoors, bury deep in garden soil, install support cage or stake early, keep well-watered but not soggy

Flowering

3-4 weeks

Plant 12-24 inches tall with multiple flower clusters forming along stems, first flowers appearing in distinctive yellow clusters

Maintain consistent watering and nutrients, consider light fertilizing with balanced fertilizer (5-5-5) or tomato-specific blend, prune suckers to 1-2 main stems for larger fruit, support heavily with stakes or cages

Fruiting

4-6 weeks

Fruits setting and enlarging to marble, then golf ball, then full size; distinctive blue-purple color developing as fruit matures from green to dark purple-blue

Continue consistent deep watering, mulch around base with 2-3 inches organic mulch to regulate moisture and temperature, remove lower leaves after fruit set to improve air circulation, reduce nitrogen fertilizer, apply calcium (crushed eggshells) to prevent blossom end rot

Harvest/Mature Fruit

Until frost (6-10 weeks or more in warm zones)

Fruits reach full size (2-3 inches diameter), deep blue-purple color with some remaining red undertones, slightly soft to gentle pressure when ripe

Harvest when fully colored but still slightly firm for best flavor development; can pick at breaker stage and ripen indoors if frost threatens; continue watering and light pruning to encourage continued production until frost

Companion Planting

Plan your garden →

Plant with:

Basil Marigold Carrot Onion Parsley Borage Nasturtium Chives

Avoid planting near:

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

Common Pests

Hand-pick large caterpillars daily, use Bacillus thuringiensis (Bt) spray, encourage parasitic wasps
Spray undersides of leaves with neem oil or insecticidal soap, use yellow sticky traps, introduce beneficial insects
Increase humidity and misting, spray with neem oil or sulfur, use predatory mites in severe cases
Remove infected lower leaves, avoid overhead watering, improve air circulation, apply copper fungicide if needed
Remove affected plant parts immediately, apply chlorothalonil or copper-based fungicides, maintain good spacing and air flow
Remove infected leaves, avoid wetting foliage, apply copper fungicide, practice crop rotation

Uses

🍳

Fresh eating and gourmet salads

Culinary

Kauai Blue tomatoes have a rich, complex flavor with subtle smoky and slightly sweet notes, making them exceptional for eating fresh in salads, on sandwiches, or simply sliced with salt and olive oil. The unique color adds visual drama to any dish. [source]

🍳

Sauces and cooking

Culinary

The deep color and robust flavor make these tomatoes excellent for homemade pasta sauces, gazpacho, salsa, and cooked tomato dishes. The dense flesh resists wateriness better than some other varieties. [source]

💊

Anthocyanin-rich superfood

Medicinal

The blue-purple pigmentation indicates high anthocyanin content, compounds with antioxidant and anti-inflammatory properties. Regular consumption of these tomatoes may support cardiovascular health and reduce oxidative stress. [source]

🏠

Seed saving and heirloom preservation

Household

As an indeterminate heirloom variety, Kauai Blue seeds can be saved from fully ripe fruits and replanted year after year. This maintains genetic purity and connects gardeners to agricultural heritage. [source]

🎨

Ornamental garden display

Craft

The striking blue-purple fruits on vigorous vines create beautiful visual interest in vegetable gardens, edible landscapes, and containers, attracting both gardeners and pollinators. [source]

This is not medical advice. LizPlants is not a medical resource. Always consult a qualified healthcare professional before using plants medicinally.

Harvest Tips

Pick Kauai Blue tomatoes when fully colored (deep blue-purple throughout) and slightly soft to the touch. They can be harvested at the breaker stage (just showing color change) and ripened indoors at room temperature if needed, though vine-ripened fruit has superior flavor. For extended harvest in cool climates, pick green mature fruit 2-3 weeks before first frost and ripen indoors.

Fun Facts

🌱 Kauai Blue is believed to have originated from Hawaiian growers and represents a relatively rare example of naturally blue tomatoes; the blue pigment (anthocyanins) is more commonly found in blueberries and purple cabbage
🌱 Despite their exotic appearance, Kauai Blue tomatoes contain the same essential nutrients as red tomatoes plus additional anthocyanins, making them both beautiful and nutritionally superior
🌱 The variety name 'Kauai Blue' references the island of Kauai in Hawaii, though the exact origin story of who originally bred this variety has been somewhat lost to history, typical of many heirloom cultivars

Gardening Terms

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

Cultivar Full Sun Heirloom Mulch Sucker Transplant True Leaves

Shop Kauai Blue plants and related plants at Plant Addicts →

Join 30,000 gardeners planning their gardens with LizPlants.

Get your personalized Kauai Blue planting timeline

Tell us your zip code and we'll calculate exactly when to start Kauai Blue seeds, transplant seedlings, and harvest — based on your USDA zone and local frost dates. Includes calendar reminders and printable task lists. Free to start.

Get my Kauai Blue timeline →