What Color Should A Greenhouse Be? What Science Says

Greenhouses often come in either transparent or green. Is this because plants need light to grow or for something else? Green is a good color for growing flowers but what about vegetables? Well here are some secrets that may help your greens get big faster!

Greenhouses should be transparent to allow the entire spectrum of sunlight to penetrate the surface and be absorbed by plants. Blue and red greenhouse can promote better fruit yield and growth. Plastic polyethylene is the most common material due to its low cost and easy deployment.

Light is an all-important factor in allowing plants to produce their own food for their growth. The color of your greenhouse can have an influential effect so be informed!

Does Color Have An Effect on Plants?

The color of a greenhouse has an effect on the growth of plants. Colored greenhouse filters a certain “fraction” of light that influences plant growth and photosynthesis.

Greenhouses are made of translucent or transparent materials which act as a light filter. The color of the cover will allow different light part (also called lightwave) colors to pass while blocking others.

Example: When sunlight or any other light really passes through red-colored glass, the red light will pass through while other wavelengths will be absorbed. Magenta-colored glass will absorb green light but will allow blue and red light to pass through.

This is why stained glass illuminates the insides of a cathedral with different hues of light when light strikes the glass.

What Is the Best Color for a Greenhouse?

The best color for a greenhouse should be clear, transparent plastic or glass. Clear and transparent materials allow for most of the light spectrum to penetrate the greenhouse and the plants therein.

Fortunately, most commercially available greenhouses come in clear covers to allow most of natural light to penetrate and be absorbed by the plants.

Effect of Greenhouse Color on Plant Growth

Scientific sources have differing conclusions on the effects of different greenhouse cover colors on plant growth. This depends on the type of plants with some being more or less receptive to certain bands of light relative to others.

Just to be clear,

This section can only provide a general guide. Different plants react differently to different light wavelengths (or colors). We can infer some conclusions based on a limited amount of studies or our and other expert gardener anecdotes.

1 – Clear/Transparent

Clear and transparent greenhouses allow the full-light spectrum to penetrate the greenhouse is the best for plant growth and development since this is the light plants naturally absorb from sunlight.

Using clear/transparent plastic, glass, polycarbonates, or fiberglass covers on a greenhouse provides for a controlled growing environment. Studies have often used clear/transparent materials as the “control” group by which all other variables are compared against.

Clear and transparent greenhouses are the most common greenhouse option available in the market because of these qualities.

2 – Green-Colored

Green-colored greenhouse colors and green light are less influential on plants. Michigan State University states that while green light might be useful for plant architecture or structure regulation, it is the least efficient wavelength in the visible spectrum for photosynthesis.

However, it is curious that green covers are commonplace for greenhouses in the market. Sometimes the green is integrated into the plastic, sometimes the transparent greenhouse is covered by a green net.

One explanation is that the green covers help reflect excess light, reducing light intensity and temperature inside the greenhouse. Another practical reason why green covers are so commonplace for greenhouses is that they’re more aesthetically pleasing than just clear plastic, allowing a better blend in a field or garden.

3 – Red-Colored

Red-colored greenhouses and red light result in reduced plant height but greater fruit yield and accelerated flowering. This process is even more significant if a red light source is used in conjunction with red covers.

Some scientific sources and gardener anecdotes report that red light (600-850 nm) promotes faster and prolonged flowering. In this case, red-colored greenhouses would be best suited to flower or fruit gardening.

Given the general effect of reduced stem and overall height, red should not be selected if those are the desired qualities. Plants grown under red light generally have a stretched and elongated appearance with thin, large leaves.

4 – Blue-Colored

Blue-colored greenhouses and blue light result in higher fruit number, weight, and yield. At higher intensities, it promotes flowering in long-day plants and inhibits flowering in short-day plants. Plants under blue light exhibited darker, greener leaves and shorter height overall.

Blue light is radiation with wavelengths between 400-500 nm and has high energy which is useful for plant growth. Low intensities of blue light present in regular light are enough to promote proper plant growth and development. At higher intensities, its effect may vary – some plants being more receptive than others.

Generally, plant growth is suppressed under blue light. Leaves may respond positively under blue light like in leafy greens wherein there is an increase in antioxidants and vitamins.

At high intensities, flowering is promoted for long-day plants, those which flower with just a few daylight hours (less than 12) such as spinach and lettuce. On the other hand, flowering is inhibited for short-day plants, those which flower only during summers when days are way longer than nights (more than 12 hours) such as soybeans and chrysanthemums.

5 – Yellow-Colored

Yellow-colored greenhouses and yellow lights have the least effect on plant growth and development and so are not generally recommended

Studies and gardener anecdotes report that removing or reducing yellow light (580 nm) may improve plant growth and development when growing in a greenhouse.

4 Common Greenhouse Cover Materials

Apart from knowing the color of your greenhouse, it’s also important to know what kind of material they’re made of. The material has an effect on the durability and the ability of light to pass through the greenhouse.

The materials that greenhouses are generally made of are: 1) plastic polyethylene (PE), 2) glass, 3) polycarbonate, and 4) fiberglass.

1 – Plastic Polyethylene (PE)

Polyethylene (PE) is a common material for greenhouses because it allows ~85% of natural light to penetrate the greenhouse and reach the plants while still being inexpensive.

Inexpensive polyethylene plastic covers will only last for a year or two. More expensive and more durable polyethylene materials with UV-resistant coating are available which allow it to last 4-8 years with proper washing.

This is indeed the most common option for greenhouses.

2 – Glass

Glass is a durable material that allows (when clean) around 90% of natural light to pass through and reach the plants.

Glass is a better material for permanent greenhouse installations since it is the longest-lasting greenhouse material available. It is also the most expensive, with tempered glass costing more than the double-strength glass panes commonly used.

3 – Polycarbonate

Polycarbonate is a flexible, durable, plastic material that allows ~90% of light to penetrate the greenhouse and reach the plants.

Polycarbonates can last for around 10 years but can be quite costly. This cost is attributed to its flexibility, durability, available coating options, and more difficult manufacturing process. As such, polycarbonate is better suited for a more permanent greenhouse installation.

4 – Fiberglass

Fiberglass is another durable plastic material that allows ~75-90% of light to penetrate the greenhouse and reach the plants.

This material can last for around 20 years making it another good option for a permanent greenhouse installation. Fiberglass also has good heat retention qualities which make it a suitable candidate in colder climates. They can also come in greenhouse quality clear or frosted panels.

Fiberglass is way more expensive than polyethylene covers and is much better for long-term growing.

Shade Cloth or Shade Nets

Greenhouse shade cloths (aka shade nets) are made from knitted polyethylene fabric, providing protection and shade over a greenhouse. Shade cloths are ideal in areas with long hours of clear sky and high summer temperatures to protect plants from excessive heat.

Shade cloths provide improved ventilation and light diffusion. It also has the added benefit of reflecting the harsh summer heat and keeping plants cool.

They come in a variety of sizes and densities to fit different purposes, from agricultural to animal husbandry. Shade cloths can also be used for grazing animals in the field to shield them from the heat.

A study states that peppers grown under four different shade cloths with a relative shading of 40-50% have improved fruit yield by 113-131% compared to those grown in an open field. The increased productivity is attributed to the shade net moderating climatic extremes, making sure that plants are shielded from excess heat.

Takeaways

1. The color of the greenhouse has a significant effect on the growth of plants therein. The color of the greenhouse can filter out and only allow certain wavelengths of light.
2. A clear or transparent greenhouse covers are the best choice since it allows most wavelengths of natural light to penetrate it and reach the plants.
3. A shade cloth or net can be a good way to improve plant yield by protecting them from climatic extremes.

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