How to Grow Organic Vegetables in a Greenhouse: A Complete Guide

How to Grow Organic Vegetables in a Greenhouse

A comprehensive guide to sustainable, year-round vegetable production

Why Grow Organic Vegetables in a Greenhouse?

Extended Growing Season

Grow vegetables year-round regardless of external weather conditions, extending your harvest well beyond traditional seasons.

Controlled Environment

Manage temperature, humidity, and watering with precision, creating ideal growing conditions for various vegetables.

Pest Protection

Reduce pest problems naturally and minimize the need for intervention by creating a protected growing environment.

Planning Your Greenhouse

Structure & Location

1

Southern Exposure – Position your greenhouse to receive maximum sunlight, ideally with southern exposure for northern hemisphere locations.
2

Size & Height – Consider ceiling height for tall plants like tomatoes. Minimum recommended height: 7-8 feet at center.
3

Materials – Choose between glass (excellent light, durable), polycarbonate (good insulation, diffused light), or polyethylene film (affordable, needs replacement every few years).

Essential Components

Ventilation System

Include roof vents, side vents, and possibly fans to maintain air circulation and prevent disease.

Irrigation Setup

Drip irrigation systems are most efficient for greenhouses, conserving water and providing consistent moisture.

Temperature Control

Consider both heating for winter and cooling/shading for summer to maintain optimal growing temperatures.

Raised Beds vs. Container Systems

Raised Beds

Ideal depth: 15-30cm (6-12″) for most vegetables
30cm (12″) or deeper for root crops
Better soil temperature stability
Improved drainage and root development
Lower watering frequency needed

Container Systems

More flexible arrangement
Easier to rotate crops and manage diseases
Better for limited space greenhouses
May require more frequent watering
Good for shallow-rooted crops and herbs

Organic Soil Preparation

The foundation of successful organic greenhouse growing is healthy, living soil. Unlike conventional methods that rely on synthetic fertilizers, organic growing focuses on building soil ecosystem.

Base Soil Mix

40% high-quality topsoil
30% finished compost
20% coconut coir or peat moss
10% perlite or vermiculite

Organic Amendments

Worm castings (microbe-rich)
Bone meal (phosphorus source)
Kelp meal (micronutrients)
Rock dust (minerals)

Natural Fertilizers

Compost tea for microbial boost
Fish emulsion for fast nitrogen
Alfalfa meal for slow-release nutrients
Bat guano for flowering/fruiting

Making Compost for Your Greenhouse

Ingredients to Include:

Green materials (nitrogen): vegetable scraps, coffee grounds, fresh grass clippings
Brown materials (carbon): dry leaves, straw, shredded paper, wood chips
Maintain a ratio of approximately 2:1 browns to greens
Small amounts of soil to introduce beneficial microorganisms

Composting Process:

Layer browns and greens in your compost bin
Keep moisture level similar to a wrung-out sponge
Turn pile every 1-2 weeks to aerate
Finished compost should be dark, crumbly, and earthy-smelling
Typically takes 2-6 months depending on conditions

Pro Tip: Soil Testing

Test your greenhouse soil annually to monitor pH and nutrient levels. Most vegetables prefer a pH between 6.0 and 7.0. Adjust accordingly using organic materials like lime (to raise pH) or sulfur (to lower pH).

Climate Control & Watering

The primary advantage of greenhouse growing is environmental control. Maintaining optimal conditions ensures healthy plant growth and maximum yields.

Temperature Management

Vegetable Type	Day Temp (°F)	Night Temp (°F)
Cool Season (lettuce, spinach)	65-75	45-55
Warm Season (tomatoes, peppers)	75-85	60-70
Root Vegetables (carrots, beets)	60-70	50-60

Temperature Control Methods:

Heating: Electric heaters, solar heat storage, compost heat systems
Cooling: Shade cloth (30-50% density), roof vents, evaporative coolers
Automation: Thermostat-controlled fans and vents reduce manual management

Humidity & Ventilation

Most vegetables thrive in 60-80% humidity. Higher levels increase disease risk; lower levels stress plants.

Effective Ventilation Strategy:

Install roof vents at the highest point of the greenhouse
Add side vents near the bottom for air circulation
Use oscillating fans to prevent stagnant air pockets
Ventilate daily, even in winter (briefly during mid-day)

Watering Systems

Drip Irrigation

Best choice for most greenhouse crops. Delivers water directly to soil, reducing disease and water waste.

Self-Watering Containers

Reduces frequency of watering and provides consistent moisture levels.

Smart Irrigation

Sensors monitor soil moisture and automate watering based on actual needs.

Rainwater Collection

Sustainable water source free of chlorine and other chemicals.

Pro Tip: Morning Watering

Water in the morning to allow foliage to dry during the day, reducing disease pressure. Avoid evening watering which can create damp conditions overnight.

Planting & Growing Techniques

Crop Selection & Timing

Choose vegetables based on your greenhouse conditions and available space. Consider succession planting to maximize yields.

Season	Best Greenhouse Crops
Winter	Spinach, kale, mâche, chard, carrots, radishes
Spring	Lettuce, peas, arugula, Asian greens, early tomatoes
Summer	Tomatoes, cucumbers, peppers, eggplant, basil
Fall	Broccoli, cauliflower, cabbage, beets, turnips

Spacing Guidelines:

Tomatoes: 18-24 inches between plants
Peppers/Eggplant: 15-18 inches between plants
Cucumbers: 12-18 inches (with vertical trellising)
Leafy Greens: 6-10 inches between plants
Root Vegetables: 2-4 inches (carrots, radishes), 4-6 inches (beets)

Companion Planting

Strategically plant compatible vegetables together to enhance growth, deter pests, and improve flavor.

Vegetable	Good Companions	Poor Companions
Tomatoes	Basil, carrots, onions	Potatoes, cabbage, corn
Cucumbers	Beans, peas, sunflowers	Potatoes, aromatic herbs
Lettuce	Carrots, radishes, strawberries	None significant
Peppers	Basil, onions, carrots	Fennel, kohlrabi

Crop Rotation

Even in greenhouse settings, practice crop rotation to prevent soil-borne disease buildup and nutrient depletion.

4-Year Rotation System:

Year 1: Leafy crops (lettuce, spinach)
Year 2: Fruit crops (tomatoes, peppers)
Year 3: Root crops (carrots, beets)
Year 4: Legumes (peas, beans)

Vertical Growing Strategies

Maximize your greenhouse space by growing upward. Vertical techniques can double or triple your growing area.

Trellising

Use string, netting, or premade trellises for tomatoes, cucumbers, and peas. Train plants weekly.

Hanging Baskets

Perfect for strawberries, herbs, and trailing cherry tomatoes. Position to avoid shading other plants.

Tiered Shelving

Place shorter plants (lettuce, herbs) on shelves above root crops or shade-tolerant varieties.

Organic Pest & Disease Management

Preventing problems is easier than treating them. Regular monitoring and early intervention are key to organic pest management.

Common Greenhouse Pests

Pest	Signs	Organic Controls
Aphids	Curling leaves, sticky residue	Insecticidal soap, neem oil, ladybugs
Spider Mites	Fine webbing, stippled leaves	Increasing humidity, predatory mites
Whiteflies	Tiny white insects that fly when disturbed	Yellow sticky traps, insecticidal soap
Fungus Gnats	Small flies around soil, weak plants	Dry top soil, BTI treatments, yellow traps

DIY Insecticidal Soap Recipe:

1 tablespoon mild liquid soap (not detergent)
1 quart (4 cups) water
Optional: 5 drops of neem oil
Mix in spray bottle and apply to affected plants
Test on a small leaf area first

Disease Prevention

Proper Air Circulation – Use fans to keep air moving. Prune plants for better airflow between leaves.

Proper Watering – Water at soil level rather than on foliage. Morning watering allows leaves to dry during the day.

Plant Spacing – Avoid overcrowding to reduce humidity around plants and prevent disease spread.

Sanitation – Remove diseased plant material immediately. Clean tools between plants when disease is present.

Beneficial Insects

Introduce nature’s pest controllers to maintain ecological balance in your greenhouse:

Ladybugs

Controls aphids, mites, and small soft-bodied insects

Lacewings

Voracious predators of aphids, thrips, and mealybugs

Predatory Mites

Specifically target spider mites and thrips

Parasitic Wasps

Control caterpillars, aphids, and whiteflies

Pro Tip: Weekly Scouting

Set a regular time each week to examine plants closely. Look under leaves and at stem joints where pests often hide. Early detection is critical for successful organic pest management.

Harvesting & Maintenance

Harvesting Best Practices

Proper harvesting techniques improve flavor and can increase overall yield.

Harvest in the Morning – Vegetables have the highest water content and crispness in the morning.
Use Sharp Tools – Clean, sharp scissors or knives make clean cuts that heal quickly and prevent disease entry.
Regular Harvesting – Many vegetables (like cucumbers, beans, and zucchini) produce more when harvested frequently.
Handle with Care – Avoid bruising produce, as damage reduces storage life and can introduce pathogens.

Harvesting Timelines:

Leafy Greens: Pick outer leaves as needed or harvest entire plant
Tomatoes: Harvest when fully colored but still firm
Cucumbers: Pick when 6-8 inches long (slicing) or 3-5 inches (pickling)
Peppers: Harvest at green stage or wait for color change (red, yellow, orange)
Root Vegetables: Pull when they reach desired size

Seasonal Maintenance

Spring Tasks:

Clean and disinfect all surfaces
Check and repair greenhouse structure
Prepare soil beds and add fresh compost
Test and repair irrigation systems
Start heat-loving crops (tomatoes, peppers) indoors

Summer Tasks:

Install shade cloth before temperatures peak
Check ventilation systems are working properly
Monitor for pests more frequently (every 2-3 days)
Increase watering as needed
Harvest regularly and start fall crops

Fall Tasks:

Remove shade cloth as temperatures decrease
Test heating systems before cold weather
Plant cold-hardy winter crops
Clean gutters and drainage systems
Prepare insulation if needed for winter

Winter Tasks:

Check greenhouse for drafts and heat loss
Remove snow from roof when accumulating
Reduce watering frequency
Plan next season’s layout and order seeds
Maintain heating system

Pro Tip: Record Keeping

Maintain a greenhouse journal documenting planting dates, varieties, yields, pest issues, and what worked well. This information becomes invaluable for planning future seasons and improving your results year after year.

Getting Started: Your First Steps

1

Start Small – Begin with a manageable greenhouse size and a few vegetable varieties you enjoy eating.
2

Focus on Soil – Invest time in building healthy, living soil as the foundation of your greenhouse garden.
3

Monitor Daily – Spend time each day observing your plants and greenhouse environment.
4

Learn and Adapt – Each season will teach you something new. Be willing to adjust your methods based on results.
5

Connect with Other Growers – Join local gardening groups or online forums to share knowledge and experiences.

Happy Gardening…