Can I use grow lights in a greenhouse?

Using grow lights in a greenhouse can be highly beneficial for supporting plant growth. Greenhouses allow gardeners to grow plants year-round by creating an ideal microclimate, but natural light levels can be too low during cloudy weather or winter months. Supplementing with artificial grow lights provides the intense light that plants need for robust growth and maximum yields.

What are the benefits of using grow lights in a greenhouse?

There are several key benefits to using grow lights in a greenhouse:

• Extend the growing season – Grow lights allow earlier seed starting and later harvests by supplementing natural light in early spring, late fall, and winter.
• Boost growth and yields – The intense light drives faster growth, bigger plants, and higher yields compared to relying solely on natural light.
• Grow light-loving plants – Certain plants like orchids and cacti thrive under direct grow lights. Supplemental lighting enables growing these light-hungry plants in a greenhouse.
• Consistency – Grow lights provide steady, reliable light levels compared to fluctuating natural light. This consistency benefits plant growth.
• Control – Being able to adjust the timing, intensity, color, and positioning of grow lights allows for precise control over the light environment.

The controlled environment of a greenhouse paired with customized grow light settings creates ideal growing conditions resulting in healthy, productive plants.

What types of grow lights work well in a greenhouse?

There are several types of grow lights suitable for greenhouse use:

LED Grow Lights

LED (light emitting diode) grow lights are one of the most popular options for greenhouses. Benefits of LEDs include:

• Energy efficiency – LEDs consume up to 50% less electricity than other types of grow lights.
• Long lifespan – LEDs can last up to 50,000 hours before needing replacement.
• Cool operation – LEDs produce very little heat, avoiding the need for ventilation systems.
• Compact size – Small, lightweight design makes LEDs easy to install in any space.
• Directional light – LEDs focus light directly downward, maximizing intensity for plants.
• Customizable spectra – Choose LED systems that provide the ideal light colors for each crop.

High-Intensity Discharge (HID) Lights

HID grow lights include metal halide and high-pressure sodium options. Benefits include:

• Intensity – HID lights produce an extremely bright, penetrating light that is suitable even for large greenhouse spaces.
• Light color options – Metal halide emits a blue-toned light while high-pressure sodium produces orange-red hues. The ability to alternate between the two provides different benefits at various growth stages.
• Proven results – HID lighting has been the industry standard for decades, with a reputation for reliably producing robust plant growth.

Fluorescent Grow Lights

Standard fluorescent tubes or compact fluorescents are inexpensive options for small greenhouses. Pros of fluorescent lighting include:

• Wide availability – Fluorescents lights are readily available at hardware stores and garden centers.
• Low cost – Both purchase price and operating costs are lower compared to other grow light systems.
• Simple setup – Fluorescents can run on standard outlets and are easy to install.
• Low heat – Fluorescents operate cooler than HID options, reducing the need for greenhouse ventilation.

What factors should be considered when using grow lights in a greenhouse?

Successfully installing and operating grow lights in a greenhouse depends on several factors:

Type of Plants

Consider the exact plants you intend to grow. Leafy greens, herbs, and flowers generally require lower light levels than fruiting vegetables and cannabis. Make sure to choose a grow light intensity adequate for the crops you want to cultivate.

Time of Year

Determine when your greenhouse will require supplemental lighting. In northern climates, grow lights may be needed year-round. In southern regions, they may only be necessary in winter. Installing timers or connecting lights to a photoperiod controller can automate seasonal adjustments.

Greenhouse Size & Layout

Size the grow light system appropriately for the square footage being illuminated. Layout greenhouse benches and hanging grids to ensure an even distribution of light. Factor in headroom required between the tops of plants and lights.

Humidity & Temperature Control

Consider how the heat from grow lights may impact temperature and humidity inside the greenhouse. Proper ventilation and air circulation are important to prevent issues. You may need to install exhaust fans, passive vents, or other climate control mechanisms when adding grow lights.

Energy Efficiency

Choose energy efficient LED or fluorescent lights whenever possible to save on electrical costs. Installing timers, photoperiod controllers, and motion sensors also help optimize energy use based on real-time light and equipment needs.

What are the best practices for using grow lights in a greenhouse?

Following some key best practices will help ensure your supplemental greenhouse lighting is effective:

• Provide 16-18 hours of light per day for most plants. Time lights to switch on before sunrise and switch off after sunset.
• Position top-mounted lights 1-2 feet above plants and adjust height as crops grow taller.
• Angle lights to hit plants directly and maximize coverage across the entire greenhouse.
• Use reflective surfaces on walls and floors to increase light diffusion throughout the space.
• Clean bulbs, lenses, and reflectors regularly to maintain peak light intensity.
• Ventilate greenhouse and/or use circulation fans to prevent excessive heat buildup.
• Start seeds and young plants under fluorescent or LED lights before moving to higher output HID lights.

Should grow lights be used for all plants in a greenhouse?

While most plants benefit from supplemental lighting, grow lights may not be required for all crops in a greenhouse. Consider the natural light needs and peak lighting hours for each variety you intend to grow.

Low light plants like African violets, orchids, and succulents often require less than 12 hours of light per day. Too much intense light can actually damage these species. They would thrive under a combination of natural daylight and minimal grow light exposure.

Leafy greens like lettuce, kale, arugula, and herbs also grow well under ambient greenhouse light during sunny months. Supplementing with grow lights may be unnecessary if the greenhouse receives a suitable amount of natural light already.

Prioritize grow light installation over plants that require high intensity light for robust growth and fruiting. This includes tomatoes, peppers, cucumbers, cannabis, and most flowering and fruiting crops. The extra light drives faster growth and greater yields.

What are the potential drawbacks of using grow lights in a greenhouse?

While grow lights provide many benefits, there are also some potential downsides to consider:

• Heat – Excessive heat from grow lights can damage plants. Proper ventilation and air circulation are essential.
• Altered growth habits – Too much uninterrupted light can cause abnormal stretching and affect fruiting.
• Higher energy costs – Grow lights increase electricity usage, especially with outdated HID lighting.
• Light pollution – Excessive glare and light trespass can affect nearby properties and disrupt natural cycles.
• Hazardous bulbs – HID and fluorescents contain hazardous materials requiring specialized disposal.
• High upfront costs – Installing grow light systems can require a hefty upfront investment.

Being mindful of these factors and taking the proper precautions will help avoid potential issues.

Conclusion

Grow lights are a worthwhile investment for greenhouses to optimize light conditions for healthy, thriving plants year-round. LED and HID lighting provides intense supplemental light that drives faster growth and higher yields for most crops. When installing greenhouse grow lights, it is important to choose an appropriate system for your space, control heat buildup, provide adequate height for adjustments, and tailor exposure times to the needs of each plant variety. Following best practices for positioning and maintaining the grow lights will ensure your greenhouse receives the maximum benefits.