Greenhouse gardening offers a controlled and efficient environment for growing crops during the summer, allowing for extended growing seasons and protection from external weather fluctuations. By choosing the right crops that are scientifically suited for greenhouse conditions, growers can significantly improve yields and reduce pest and disease risks.
Summer poses unique challenges for greenhouse cultivation, such as managing heat buildup, regulating humidity, and optimizing light exposure. However, these challenges also create opportunities for cultivating high-demand crops that thrive under warm, humid, and light-rich conditions.
This article explores the best summer crops for greenhouses, grounded in scientific research and horticultural best practices. From fruiting vegetables like Solanum lycopersicum (tomato) to nutrient-rich leafy greens and specialty herbs, we provide a data-driven guide to help greenhouse growers maximize productivity and quality during the summer season.
Understanding Summer Growing Conditions in Greenhouses
Successfully growing crops in summer greenhouses requires a deep understanding of microclimate management. Key factors such as temperature, humidity, and light intensity must be precisely controlled to mimic optimal growing conditions.
Temperature and Humidity Control
USDA and horticultural studies show that most summer crops thrive between 70–85°F (21–29°C). To maintain this range, growers should utilize ventilation systems, automated fans, and shading cloths. High humidity above 70% can increase the risk of fungal infections like powdery mildew, while low humidity can hinder transpiration and nutrient uptake.
Light Requirements and Shading
Photosynthetically Active Radiation (PAR) plays a vital role in plant development. Crops like tomatoes and peppers require 14–18 hours of light daily. Supplemental LED lighting and reflective surfaces can be used to maintain light intensity. During peak summer, shade cloths (30–50%) help prevent heat stress and photoinhibition.
Pest and Disease Management
Warm, humid environments are conducive to pests such as whiteflies, aphids, and spider mites. Integrated Pest Management (IPM) practices, including introducing predatory insects like Encarsia formosa and environmental control strategies, effectively maintain a pest-free greenhouse.
Top Fruit-Bearing Crops for Summer Greenhouses
Fruit-bearing crops are a favorite for greenhouse growers during summer due to their high market value and productivity. Crops like tomatoes, peppers, and cucumbers can reach peak performance when optimal growing conditions are provided in a controlled environment. Each crop has specific physiological needs that can be effectively met within a greenhouse setup.
Tomatoes (Solanum lycopersicum)
Tomatoes are arguably the most popular summer greenhouse crop. They are highly responsive to controlled environments, where temperature, humidity, and light exposure can be finely tuned to support flowering, fruit set, and ripening.
Best Greenhouse Varieties
Research from the University of California Cooperative Extension suggests that indeterminate varieties like 'Trust F1', 'Geronimo', and 'Sakura' perform best in greenhouses due to their continuous production and disease resistance. Cherry and grape types also thrive, especially in smaller greenhouses with vertical space.
Pollination and Pruning
Greenhouse tomatoes require manual or assisted pollination. Vibrating tools or using bumblebees (Bombus terrestris) can significantly increase fruit set. Pruning to a single stem and regularly removing suckers improves airflow and directs nutrients to fruit development.
Soil and Nutritional Needs
Optimal soil pH ranges from 6.0 to 6.8. Tomatoes are heavy feeders; therefore, a balanced N-P-K ratio (10-10-10 or 5-10-10 during fruiting) and calcium and magnesium supplementation are recommended. Monitoring the soil's electrical conductivity (EC) can help maintain nutrient balance.
Peppers (Capsicum annuum, Capsicum chinense)
Peppers thrive in warm, sunny greenhouse environments, including sweet bell peppers and hot chili varieties. They benefit significantly from stable conditions, which reduce blossom drop and increase fruit yield.
Varietal Selection
Greenhouse-recommended varieties include 'California Wonder' for bell peppers and 'Habanero Orange' for hot types. These cultivars resist common greenhouse pests and diseases, such as aphids and bacterial spots.
Temperature and Watering Needs
Peppers grow optimally between 75–85°F (24–29°C). Soil moisture should be kept consistent to prevent blossom end rot, often caused by calcium deficiency. Mulching and drip irrigation are recommended to maintain stable moisture levels.
Scientific Insights
Studies published in the Journal of Horticultural Science show that peppers respond well to potassium-rich fertilizers during the flowering and fruiting stages. Using reflective mulches can also increase yield by enhancing light distribution in the lower canopy.
Cucumbers (Cucumis sativus)
Cucumbers are fast-growing and prolific in greenhouses when provided with vertical support and consistent moisture. They require high light and humidity for optimal fruit set and disease resistance.
Bush vs. Vining Types
Vining cucumbers such as 'Telegraph Improved' or 'Socrates F1' are favored in greenhouses for their high yield and adaptability. Bush varieties can be used in more miniature greenhouses with limited space.
Trellising and Growth Optimization
Trellising cucumbers vertically increases airflow, reduces disease risk, and maximizes space efficiency. It also encourages uniform fruit development and easier harvesting.
Scientific Notes
According to research from Wageningen University, optimal fruit production in cucumbers occurs when relative humidity is maintained between 60% and 70%, and CO2 enrichment enhances vegetative growth and fruit size.
Lettuce prefers soil pH between 6.0 and 6.5 with high organic matter. Cornell University studies support compost teas and fish emulsions to boost growth without causing nitrate accumulation.
Spinach (Spinacia oleracea) and Swiss Chard (Beta vulgaris subsp.. cicla)
Both spinach and Swiss chard are nutrient-rich leafy greens with moderate tolerance to greenhouse heat when bolting-resistant varieties are used.
Varietal Recommendations
For spinach, 'Tyee' and 'Corvair' are favored due to their resistance to bolting and downy mildew. For Swiss chard, 'Bright Lights' and 'Fordhook Giant' offer vibrant colors and adaptability to warm conditions.
Scientific Cultivation Tips
Research from the International Society for Horticultural Science suggests planting in slightly shaded zones with frequent irrigation reduces leaf bitterness and prevents stress-induced bolting. Soil should remain consistently moist but well-drained.
Nutrient Profile and Soil Management
Both crops benefit from nitrogen-rich soil, but excess levels must be avoided, especially in spinach, which is prone to nitrate buildup. A balanced organic fertilizer (e.g., 4-3-3) is often sufficient.
Basil and Other Herbs (Ocimum basilicum)
Basil thrives in warm, sunny greenhouses and is a key aromatic herb with medicinal and culinary uses. Its fast growth and high demand make it an ideal summer crop.
Companion Planting and Benefits
Basil is known to repel pests and can be intercropped with tomatoes or peppers to enhance flavor and reduce insect pressure. Studies show that allelopathic properties from basil roots can positively influence nearby crops.
Harvesting for Best Flavor
Scientific findings suggest harvesting in the early morning preserves the highest essential oil concentration. Continuous harvesting of top leaves encourages bushier growth and more yield over time.
Greenhouse Management Tips
Ideal growth occurs at 70–85°F (21–29°C) with well-drained, fertile soil. Basil prefers a pH range of 6.0 to 7.0. Avoid water on leaves to prevent fungal infections such as Fusarium wilt.
Managing Soil Health and Fertility in Summer
Healthy soil is the foundation for successful greenhouse crop production. Managing fertility, moisture retention, and microbial activity in summer is crucial to preventing nutrient leaching and heat-related soil degradation.
Organic vs. Inorganic Fertilizers
Organic fertilizers such as compost, worm castings, and well-aged manure provide slow-release nutrients and enhance soil microbial diversity. In contrast, inorganic options offer immediate nutrient availability but may lead to salt buildup in enclosed greenhouse systems if overused.
Crop Rotation and Soil Amendments
Rotating crops within raised beds or containers reduces pathogen buildup and pest cycles. Studies from the American Society for Horticultural Science emphasize rotating heavy feeders (like tomatoes) with legumes to improve nitrogen availability naturally. Adding perlite, vermiculite, or biochar enhances aeration and water retention in summer heat.
Scientific Approach to Fertility
Soil testing and pH monitoring are essential. Maintaining a pH of 6.0–6.8 for most summer crops supports nutrient uptake. Supplementing with mycorrhizal fungi enhances root surface area and nutrient absorption efficiency, especially in phosphorus-poor soils.
Integrated Pest Management (IPM) Strategies
IPM involves a combination of biological, cultural, physical, and chemical tools to manage pests with minimal environmental impact. This approach is highly effective in greenhouses where the ecosystem can be closely monitored and controlled.
Beneficial Insects
Predatory insects such as Encarsia formosa (whitefly control), Phytoseiulus persimilis (spider mite control), and Aphidius colemani (aphid control) are widely used. These biological agents offer targeted control without the risk of chemical residues.
Organic Pesticides and Biological Controls
Neem oil, insecticidal soap, and Bacillus thuringiensis (Bt) are standard organic solutions. University extension trials show that neem oil effectively disrupts insect growth cycles when applied in the early morning or late evening to avoid plant burn.
Scientific IPM Planning
Regular monitoring using yellow sticky traps and biweekly scouting helps detect pest outbreaks early. Implementing crop sanitation, air circulation, and companion planting (e.g., marigolds) enhances overall pest resistance.
Watering Techniques for Summer Crops
Adequate irrigation during summer prevents heat stress and nutrient imbalances while minimizing water waste. Greenhouse growers must balance soil moisture and humidity to maintain optimal crop health.
Drip Irrigation vs. Overhead Watering
Drip systems offer precise, root-zone watering and reduce leaf wetness, which minimizes disease risk. While overhead systems are easier to install, they can raise humidity and spread fungal spores. Most scientific studies favor drip irrigation for its efficiency and consistency.
Managing Humidity and Fungal Issues
High humidity in summer can encourage fungal growth. Evapotranspiration models recommend watering early in the day to allow foliage to dry before nightfall. Mulching and using hygrometers to monitor air moisture help regulate the greenhouse environment.
Soil Moisture Monitoring Tools
Soil tensiometers and digital moisture meters provide real-time feedback to prevent overwatering or drought stress. Maintaining a consistent moisture level, without saturation, supports nutrient uptake and root respiration.
Harvesting and Post-Harvest Handling
Harvesting at the right time ensures peak flavor, nutritional content, and marketability. Proper post-harvest handling extends the shelf life of crops and reduces losses due to spoilage or physical damage.
Best Time to Pick Summer Crops
Tomatoes should be harvested when fully colored but still firm. Leafy greens like lettuce and spinach should be picked in the early morning when turgor pressure is highest, improving crispness. Fruits like melons should be harvested when the "slip" stage is reached—when the fruit naturally detaches from the stem.
Storage Tips for Extended Shelf Life
Different crops require unique storage conditions. To preserve flavor, tomatoes are best stored at 55–70°F (13–21°C), while leafy greens prefer cooler, high-humidity conditions around 32–36°F (0–2°C). Using breathable containers and rapid cooling after harvest can reduce microbial activity.
Scientific Insights
Research from the Postharvest Technology Center at UC Davis emphasizes the importance of minimizing ethylene exposure among ethylene-sensitive crops (e.g., lettuce near tomatoes). Proper sanitation of tools and storage areas prevents cross-contamination and decay.
Conclusion
Greenhouse gardening in the summer offers unique opportunities for producing high-yield, high-quality crops. Growers can ensure a successful and sustainable harvest by selecting scientifically backed varieties, managing microclimates, and employing integrated soil, water, and pest control strategies.
Whether cultivating tomatoes, herbs, or specialty fruits, careful planning and adherence to best practices can transform your greenhouse into a productive oasis. Don’t hesitate to experiment and adapt your practices based on ongoing observations and research findings.
FAQs
1. What are the best greenhouse varieties of tomatoes for summer?
Indeterminate varieties like Gothic Arch Cypress Greenhouse are ideal due to their disease resistance and continuous fruiting habits.
Shop the Gothic Arch Cypress Greenhouse – Elegant Design, Superior Durability
2. Can I grow tropical fruits in my summer greenhouse?
Yes, crops like bananas, pineapples, and papayas can be grown with controlled temperature and humidity, but they require significant space and resources.
3. How do I use scientific methods to control humidity in a summer greenhouse?
Use ventilation, shade cloth, and hygrometers to monitor and adjust humidity. Watering early in the day allows foliage to dry and reduces fungal risks.
4. What is the ideal greenhouse temperature range for summer crops?
Most summer crops thrive between 70–85°F (21–29°C) during the day and above 60°F (15°C) at night. Avoid temperature fluctuations to reduce plant stress.
5. Do I need specially formulated soil for optimal crop nutrition?
While standard potting mixes can work, compost-rich, well-draining soil with balanced pH and added biochar or perlite improves fertility and moisture retention.