Beyond Cannabis: Using HPS Lights for Vegetables (Tomatoes, Peppers, etc.)

While HPS lights are often associated with cannabis cultivation, they're equally effective for growing a wide variety of vegetables indoors. Their spectrum is particularly well-suited for fruiting plants like tomatoes and peppers, making them an excellent choice for year-round vegetable production.

Why HPS Works Well for Vegetables

Spectrum Advantages

The HPS spectrum offers several benefits for vegetable growing:

• Red-Orange Dominance: Rich in wavelengths that promote flowering and fruiting
• Penetration: Excellent light penetration for taller vegetable plants
• Proven Results: Decades of commercial use in greenhouse vegetable production

Vegetable-Specific Benefits

Different vegetables respond particularly well to HPS lighting:

Setting Up for Vegetable Growing

Light Intensity and Coverage

Proper light intensity is crucial for vegetable production:

• 400W HPS: Suitable for 2×2 to 3×3 ft area (4-9 sq ft)
• 600W HPS: Ideal for 3×3 to 4×4 ft area (9-16 sq ft)
• 1000W HPS: Best for 4×4 to 5×5 ft area (16-25 sq ft)

For determinate (bush) tomato varieties or pepper plants, aim for approximately 1-2 plants per square foot, depending on the variety and growing method.

Light Height and Positioning

Proper positioning is essential to avoid heat damage while providing adequate light:

• Seedlings: 24-30 inches above plants
• Vegetative Growth: 18-24 inches above canopy
• Flowering/Fruiting: 18-20 inches above canopy

Always monitor leaf temperature and watch for signs of heat stress (curling leaves, wilting). Adjust height as needed based on plant response.

Light Schedule for Vegetables

Optimal light schedules vary by growth stage:

• Seedling Stage: 16-18 hours on, 6-8 hours off
• Vegetative Growth: 16-18 hours on, 6-8 hours off
• Flowering/Fruiting: 12-14 hours on, 10-12 hours off

Unlike cannabis, most vegetables don't require strict dark periods to trigger flowering. The reduced hours during fruiting help manage energy costs while still providing adequate light for development.

Growing Specific Vegetables Under HPS

Tomatoes

Tomatoes are one of the most rewarding vegetables to grow under HPS lights:

• Recommended Varieties: Determinate types for smaller spaces (Bush Early Girl, Tiny Tim, Patio Princess), indeterminate for larger spaces with trellising (Better Boy, Beefsteak, Cherry varieties)
• Special Considerations: Require support/trellising, regular pruning of suckers, and consistent watering
• Pollination: Gently shake flowering stems daily or use a small electric toothbrush to vibrate flowers for pollination
• Typical Yield: 5-10 pounds per plant over a 3-4 month period, depending on variety

Peppers

Peppers thrive under the HPS spectrum:

• Recommended Varieties: Compact types (Hungarian Hot Wax, Cayenne, Jalapeño, Sweet Banana, California Wonder)
• Special Considerations: May need support when heavily fruiting, prefer slightly drier conditions than tomatoes
• Pollination: Same as tomatoes - gentle shaking or vibration of flowers
• Typical Yield: 20-50 peppers per plant over a 3-4 month period, depending on variety

Cucumbers

Cucumbers grow rapidly under HPS lights:

• Recommended Varieties: Bush varieties for smaller spaces (Bush Champion, Spacemaster), vining types for trellised setups (Marketmore, Straight Eight)
• Special Considerations: Require trellising for vining types, high water needs, benefit from higher humidity
• Pollination: Look for self-pollinating "gynecious" varieties for indoor growing
• Typical Yield: 10-20 cucumbers per plant over a 2-3 month period

Environmental Considerations

Temperature Management

Optimal temperatures for most fruiting vegetables:

• Day: 70-80°F (21-27°C)
• Night: 60-70°F (16-21°C)

The heat from HPS lights can be beneficial in maintaining these temperatures, particularly in cooler environments. In warmer conditions, additional cooling may be necessary.

Humidity Considerations

Most vegetables prefer moderate humidity levels:

• Seedling Stage: 65-70% RH
• Vegetative Growth: 50-70% RH
• Flowering/Fruiting: 40-60% RH

Lower humidity during fruiting helps prevent mold and disease issues. The heat from HPS lights naturally reduces humidity, which can be beneficial during fruiting stages.

Air Circulation

Proper air movement is essential when growing under HPS lights:

• Use oscillating fans to create gentle air movement throughout the canopy
• Ensure adequate ventilation to remove excess heat and maintain CO₂ levels
• Good air circulation helps prevent fungal issues and strengthens plant stems

Nutrient Requirements

Vegetables grown under HPS lights typically require:

• Vegetative Stage: Higher nitrogen (N) for leaf and stem development
• Flowering/Fruiting Stage: Higher phosphorus (P) and potassium (K) for flower and fruit development
• Calcium: Critical for preventing blossom end rot in tomatoes and peppers
• Micronutrients: Particularly important for flavor development in vegetables

Many commercial hydroponic or soil nutrient lines designed for tomatoes work well for most vegetables grown under HPS lights.

Common Challenges and Solutions

Pollination

Indoor vegetables need assistance with pollination:

• Hand pollinate using a small brush or electric toothbrush
• Gently shake flowering stems daily during flowering period
• Consider self-pollinating varieties when available

Stretching

Plants may stretch under HPS lights, especially if light intensity is insufficient:

• Maintain proper light distance
• Use gentle air movement to strengthen stems
• Consider supplemental blue light during vegetative growth

Pest Management

Common pests in indoor vegetable gardens:

• Spider Mites: Particularly problematic in the warm, dry environment created by HPS lights
• Aphids: Can quickly infest new growth
• Whiteflies: Common in indoor growing environments

Implement regular inspection routines and consider preventative biological controls like predatory mites or neem oil treatments.

Harvest and Yield Expectations

With proper care, you can expect:

• Tomatoes: First harvest 60-80 days after transplanting, continuing for 3-4 months
• Peppers: First harvest 70-90 days after transplanting, continuing for 3-4 months
• Cucumbers: First harvest 50-70 days after transplanting, continuing for 2-3 months

Under a 600W HPS in a 4×4 space, you might grow 4-6 tomato plants yielding 20-60 pounds total over a growing season, or 8-12 pepper plants yielding hundreds of peppers.

Cost-Benefit Analysis

Growing vegetables under HPS lights involves both costs and benefits:

Costs

• Electricity: A 600W HPS running 16 hours daily costs approximately £1.50-2.00 per day
• Bulb Replacement: Every 10,000-12,000 hours (approximately annual for most growers)
• Growing Medium and Nutrients: £10-20 per month for a 4×4 space

Benefits

• Year-round Production: Fresh vegetables regardless of season
• Quality Control: No pesticides, perfect ripeness, superior flavor
• Variety Selection: Grow varieties not commonly available in stores
• Educational Value: Learning experience for families and children

While growing vegetables under HPS lights may not always be cost-effective compared to store-bought produce, the quality, variety, and satisfaction of growing your own food year-round provides value beyond simple economics.