Dialing In Your Greenhouse

For commercial greenhouse growers, providing the optimal growing conditions for plants is vital to success. From humidity, temperature and lighting levels, to CO2 dispersal and ventilation, everything must be dialed in perfectly to achieve maximum yields. Here’s how the commercial operators are doing it.

It doesn’t matter if you’re a hobby or commercial grower—getting the environmental conditions just right is essential for optimal plant growth. Different stages of growth require controlled changes to replicate seasonal variations outdoors. In this article, I’ll investigate how the latest multi-million-dollar greenhouses are providing perfect environments for plants.

Many farmers have lost sleep worrying about inbound weather problems and the detrimental effects on their crop. With modern technology, farmers can rest easy knowing they can monitor and control their greenhouses from their smartphones or computers. Advanced climate control systems are capable of actively monitoring and precisely adjusting the temperature, humidity, air circulation, CO2 dispersal, UV radiation and many other parameters within a protected environment. So how do they fine-tune such wildly varying circumstances and compensate for the influences of the crop and the external ecosystem?

Start With the Layout

Initial climate control starts with a sophisticated greenhouse layout. The first aspect of this is an orientation that accounts for the changes in sun positioning during the different seasons and maximizes the potential solar energy. A gentle slope of 1-2% throughout the site increases solar gain, provides appropriate drainage and reduces site preparation costs.

Heat Management

In warmer climates, especially when you’re using HID lights, heat management is often the biggest challenge during the productive warmer months. Advanced growers use a multi-faceted approach to heat management, with a combination of vents, fans, thermal screens, water heating and cooling, and retractable roofing. Temperature probes can continuously monitor the internal and external environments and adjust the above-mentioned equipment accordingly.

A ventilation system allows natural air currents and wind gradients to remove excessive heat. The airflow circulating inside can be refreshed with circulation fans, exhaust fans and evaporative cooling fans. Horizontal airflow provides the most effective air movement through the crop and this helps with a number of plant-growth factors.

Maintaining a healthy airflow reduces fungal diseases, increases transpiration and provides fresh CO2 to plants, accelerating growth and improving overall plant health and vigor. Growers can use evaporative cooling fans to drastically reduce temperatures and maintain optimal humidity levels. This is a low-energy means of environmental control that is common for both indoor and glasshouse production systems.

The air circulation system usually works alongside automated thermal curtains, screens and shades. Thermal screens open and close to prevent excessive temperatures, provide shade and diffuse intense light energy. They maintain a more constant and comfortable greenhouse climate for the crop and staff, resulting in a more consistent harvested product. The steadier temperatures also minimize the dew that forms on crops, which reduces the risk of fungal diseases. Screens and shades are some of the most effective, budget-friendly technologies used in commercial greenhouses. By diffusing the light through specialized materials, the light energy approaches from more angles, reducing shadows and penetrating deeper into the canopy.

Adjusting for Plant Development

Different crops influence the greenhouse environment through a range of physiological processes, and growers need to be able to monitor plant growth alongside the environmental conditions and adjust accordingly. Recent technological updates allow farmers to obtain detailed plant growth analyses, giving them the ability to learn from previous results and predict future progressions in their harvests.

As plants progress through the different stages of growth, they react differently to their environments. For example, seedlings and vegetative crops generally require higher humidity levels (55-75%) than fruiting or flowering crops (45-55%). Maintaining these levels promotes more effective leaf, shoot and root development, while reducing the chances of mold or rot problems in the generative stage. If the air is too dry, plants will transpire faster, which causes slower growth, stress and trauma.

Correspondingly, plants can influence their environment by exercising their own biological processes. Large, mature, vegetative plants will transpire significantly more than seedlings or heavily fruiting crops. This can drastically influence the greenhouse’s humidity and temperature levels. A plant’s ability to transpire is influenced by the growing area’s humidity, temperature, wind and sunlight levels. The plant reacts to these factors by controlling the size of stomatal apertures to regulate the flow of water. This flow of water within the plant cools and regulates leaf and stem temperature, changes the osmotic pressure of cells and enables mass flow of mineral nutrients and water from roots to shoots.

Maintaining Humidity Levels

As we already established, if humidity levels are not appropriate for the selected crop, transpiration and growth rates are negatively affected. Automated computer programs use misting systems alongside evaporative coolers to maintain consistency and provide optimal surroundings. Misting systems are also occasionally used to deliver foliar feeding applications in certain circumstances, although this can cause problems with the fine water particle size. Most sprayers are difficult to maintain and can quickly become blocked.

Using Artificial Lighting

One factor that drastically influences environmental control is using horticultural lighting. Commercial greenhouse growers often use 1,000-W HPS luminaires, which provide a strong, yellow spectral energy to promote floral development. These lamps are used to prolong the day length during the colder months and promote faster growth, regardless of sun or cloud cover.

When using artificial lighting, higher temperature control measures are necessary, as the lamps output a significant amount of heat above the canopy. The up-front costs of the fixtures and the ongoing electricity costs must also be factored into initial greenhouse planning, along with a used-bulb recycling program.

Overhead lighting has been effectively used in horticulture for decades, but growers are starting to use lighting between the rows. Inter-lighting LED fixtures are heavily promoted in all fields of agriculture as exceptionally powerful supplementary lighting that can penetrate beneath the canopy to ripen fruit more consistently and drastically improve the yield per square foot.

Sunlight is still the most effective luminaire for plant growth and using a combination of solar energy, natural light diffusion and supplementary lighting can provide incredibly powerful conditions for growth. One limiting factor for this rapid growth is the restricted amount of carbon dioxide found naturally within an enclosed area. Many growers solve this problem by adding supplemental CO2.

Adding Carbon Dioxide

Carbon-dioxide enrichment has been used in commercial greenhouses for more than 40 years. CO2 is an essential component of photosynthesis and adding supplementary amounts stimulates speedier vegetative development by as much as 30%. CO2-enriched plants also require more water and nutrients to support the increased foliage production. Accordingly, they cannot be limited by any other critical element for life, such as low light levels or nutrient dependability.

In commercial greenhouse applications, CO2 can be added via generators, large compressed gas tanks or by capturing the flue emissions generated from a boiler. The gases are dispersed through the crop via a range of mechanisms and spread by fans. Advanced systems monitor CO2 levels and account for ambient air exchange to accurately dose the enclosed space. For most crops, CO2 levels of 800-900 ppm are ideal for maximum yields, but only if everything else is tuned to perfection.

An integrated and multi-faceted approach to environmental control provides ideal conditions in commercial greenhouses, while drastically lowering the chance of pest and disease infestations. Although it might seem challenging to achieve such ideal conditions in your home garden, it’s easier than you might think. Ask your local retailer for tips and tricks to manage climatic extremes in your area. Every greenhouse is different and has its own set of challenges to overcome, but nothing is insurmountable with a bit of logical thinking!

Original article written by Tom Forrest and published in Maximum Yield Indoor Gardening Magazine.

Online version available here