The Hoop House UK - Sun Protection for Tomato Plants
Sun protection inside a polytunnel (aka a hoop house, hot house) is essential to maintain optimal growing conditions and prevent plant damage from excessive heat and sunlight. While polytunnels allow for controlled environments, they can trap heat and light, which might harm sensitive crops. Here’s how you can manage sun protection in a polytunnel:
1. Shade Cloth
What it is: A shade cloth is a mesh-like fabric that blocks a percentage of sunlight from entering the polytunnel.
How it works: Shade cloths come in different densities, typically ranging from 30% to 90% shade. A 30% shade cloth blocks 30% of sunlight and is suitable for sun-loving plants, while a 50% or 60% shade cloth might be more appropriate for sensitive plants like leafy greens or flowers.
Installation: Shade cloths can be draped over the exterior of the polytunnel or installed inside the tunnel as an internal layer. You can either place the cloth permanently during hot periods or use it temporarily when the sun is at its peak.
Benefits: Provides controlled sun protection and reduces heat buildup without blocking too much light needed for photosynthesis.
2. Whitewash or Shading Paint
What it is: Shading paint or whitewash is a liquid solution that can be applied to the polytunnel’s plastic cover. It creates a semi-transparent coating that reflects a portion of the sunlight.
How it works: Once applied, the whitewash diffuses the sunlight entering the tunnel, reducing the intensity. This helps keep the polytunnel cooler and protects plants from getting scorched by direct sun.
Application: The whitewash can be sprayed or painted onto the outside of the tunnel. It can be washed off later in the season when less shade is needed, typically with water or rain.
Benefits: It’s an inexpensive and temporary method to manage excessive sunlight and heat. It can be adjusted based on seasonal needs.
3. Ventilation
Natural Ventilation: Keep the polytunnel ventilated by opening doors, windows, or side vents. Proper airflow can reduce excessive heat buildup and keep the environment inside the polytunnel cooler, which is important for sun protection.
Fans: For large polytunnels, you can install circulation fans to promote airflow. This helps distribute the air evenly, reducing hotspots and heat stress on plants.
Roll-Up Sides: Some polytunnels have roll-up sides that allow you to control airflow more effectively. This helps cool the interior while still protecting plants from wind or heavy rain.
4. Mulching
What it is: Mulching involves covering the soil surface with organic or synthetic materials, like straw, compost, or black plastic.
How it works: Mulch helps to insulate the soil, reduce moisture evaporation, and protect the plant’s root system from overheating. It keeps the soil cooler, even when temperatures inside the polytunnel rise.
Benefits: Mulch reduces the need for frequent watering and helps maintain stable soil temperatures.
5. Watering Techniques
Drip Irrigation: Use a drip irrigation system to provide consistent moisture to the roots of your plants without oversaturating the air inside the polytunnel. This reduces humidity, which can contribute to heat stress.
Water in the Early Morning or Evening: Water your plants early in the day or late in the evening to prevent moisture from evaporating too quickly and to cool the soil, reducing heat stress on the plants during the hottest part of the day.
6. Use of Reflective Mulch or Ground Cover
What it is: Reflective ground covers, such as white or silver plastic mulch, are designed to reflect sunlight away from the soil surface and the base of the plants.
How it works: Reflective mulch helps reduce the amount of sunlight absorbed by the soil, which lowers the temperature in the polytunnel and prevents plants from overheating.
Benefits: It keeps plants cooler, especially those close to the ground, and reduces water evaporation.
7. Double Layer Covering
What it is: Some polytunnels use double layers of polyethylene with an air gap in between. This setup helps to insulate the tunnel from extreme temperature fluctuations.
How it works: The air gap acts as an insulating barrier, reducing heat buildup from the sun and keeping the tunnel cooler during the day.
Benefits: In addition to sun protection, double layering also helps retain heat during colder periods, making it useful for year-round growing.
8. Orient the Polytunnel Properly
East-West Orientation: In areas with intense sun, positioning your polytunnel along an east-west axis ensures more even sunlight exposure throughout the day, reducing the risk of plants being scorched by the midday sun.
North-South Orientation: In regions where the sun is less intense, a north-south orientation may provide better light exposure, but you may need more shade protection during hotter months.
9. Grow Taller Plants or Companion Plants for Shade
Planting taller crops like corn or sunflowers along the sides or inside the tunnel can create natural shade for more delicate plants. These taller plants absorb some of the sun's energy and provide partial protection for the crops growing below.
Summary
To protect plants from excessive sun and heat inside a polytunnel / hoop house, you can use a variety of methods such as installing shade cloth, applying whitewash, improving ventilation, mulching, and using drip irrigation. The goal is to balance the amount of sunlight entering the tunnel while preventing overheating, ensuring your plants thrive under optimal conditions. By using these techniques, you can create a controlled environment where plants get the sunlight they need without being damaged by excess heat.
