Understand shade cloth & how its colour impacts plants ...

Weather patterns have become more inconsistent, leading to hot, dry summers in many parts of the country. Shade cloth is a tool that I’m here to tell you all about if you haven’t heard of it! So what is it exactly, and how can it help in your garden?

Shade cloth is black, white, or colored UV-treated polyethylene fabric, knitted or woven loosely or tightly. The density of the knit or weave changes the light transmittance level, which can be 30%-90%. The percentage level refers to the amount of light it blocks out.

In northern regions where the days may be long but the sun is farther from the equator and thus less likely to scald plants, many growers use 30% cloth. Most vegetables elsewhere can stand to benefit from 40% cloth for crops like tomatoes and lettuce. In hot desert regions where the sun can be damaging and brutal, growers can use 50% cloth during the peak of summer. 

The higher the percentage of cloth, the tighter the knit or weave, resulting in less light transmission. The cloth ranges in sizes to fit just one garden bed width over the top of hoops, all the way up to a gothic-style greenhouse.

Many companies offer custom-fitted sized shade cloth if you have a uniquely sized building you are looking to cover. So how can it actually help your garden? Let’s take a deeper look at what shade cloth does and the benefits it offers for gardeners.

Contents

What Does Shade Cloth Do? 

It is commonly used to cover crops like lettuce and kale, which thrive in cooler temperatures.

Shade cloth protects plants from the sun’s direct radiation and from being sunburnt, similar to how sunscreen protects humans. This UV protective layer is used on low tunnels outdoors over crops like lettuce and cool weather-loving kale. The reduction in solar radiation around the plants creates a slightly cooler temperature, which in turn decreases the need to water and increases the ability of air circulation to assist in cooling down plants during the heat. 

Shade cloth is an excellent tool to use in the garden during a heat wave.

Along with other forms of UV, shade cloth blocks harmful Ultraviolet-B Radiation (UVB radiation). The National Cancer Institute defines UVB radiation as:

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It’s pretty common knowledge that the sun can cause more damage in humans than just sunburn, and the same goes for plants. Overexposure to harmful rays can damage plant cells and DNA, decreasing plant growth and productivity.

But in addition to the UV protection that shade cloth can convey, it has an additional purpose: it blocks some of the light transmission. While the ultraviolet factor of the cloth (UVF) plays a significant role in reducing harmful ultraviolet radiation, simply blocking the light will also have a key role to play here.

Lighter-colored shade cloth can cause rays of light to refract, redirecting some of the light away from our plants. Darker-colored shade cloth simply prevents the sun’s light from fully reaching the plants by absorbing the light. In both cases, it reduces the sunlight that’s directly reaching the plants — and for some species, particularly shade-loving plants, a denser shade cloth can be the only way to grow those plants at certain times of year.

Benefits of Shade Cloth

• Helps reduce soil moisture evaporation, resulting in less watering.
• Allows natural airflow to cool the air temperatures beneath.
• You can clip it to existing hoops, raising and lowering it as needed.
• Rainwater passes through.
• Prevents excess light from reaching plants, especially when using a white or light cloth.
• Protects plants from sunscald and drying out.
• Is thought to improve light utilization by reducing harmful UV rays, resulting in increased photosynthetic activity.
• Light still reflects enough to allow plants to grow but block potentially damaging rays.
• Can be used over the top of greenhouses to cool areas where young plants are kept.
• Can be used over shade-loving perennials if you grow in a full-sun area.
• It is lightweight and easy to store.
• Fairly inexpensive with a long life expectancy.

Woven vs. Knitted Cloth 

Consider using a woven, 100% polyethylene fabric if you are growing in winter months or living in a colder region.

Most often, you’ll see that shade cloth is offered in a knitted, polyethylene blend, which helps deflect the heat of the sun while still allowing good breathability, which is important in the hotter months.  

If you are growing in winter months or live in a colder region, you might consider the alternative, which is a woven, 100% polyethylene fabric, which is a bit heavier and will help hold in the heat from the sun. 

Black vs. White Cloth 

To cope with hot summers, consider using a shade cloth in a lighter color.

Just like the clothes we wear outside in the sun, black can attract and hold in more heat, causing you to feel hot, whereas lighter colors deflect the sun’s rays, keeping you cooler. You might think that’s the same for shade cloth — but ironically, it’s not.

For most people in the southwestern US where scorching summer heat is common, black is the preferred fabric color. That’s because in most cases, black shade cloth blocks more UV rays from reaching your plants underneath. You will have a heat layer that forms just under the cloth, but as long as the cloth isn’t directly touching your plants and there is airflow, heat rises up and through the fabric.

Other colors of fabric may be more beneficial for blocking UV rays than lighter colors like yellow and white. A 2009 study identified that darker or more intense colors often blocked more UV rays than lighter-colored fabrics.

Where lighter colors are better is in their refraction rate. White or yellow shade cloth bounce more of the sun’s light away. They also still block a lot of UV; if you’re using a 40% shade cloth, you’ll still have 40% shade, but you’ll also have less of a heat layer underneath the cloth because the lighter color won’t retain the heat as well.

As a result, it’s encouraged to select lighter-colored shade cloth for areas where you plan to spend the most time, simply because it’s more likely that you’ll be up in that warm patch by the cloth itself when standing up or moving around under the cloth. Lighter-colored shade cloth is also great in desert regions where you want to reduce the intensity of the light itself by refracting it away.

When Should I Skip Shade Cloth?

Shade cloth is not universally necessary – but there are times when it can actually be detrimental, as well.

Plants considered heat-tolerant are typically bred or adapted to hot climates. These plants often can experience decreased productivity, loss of sweetness or flavor, or other changes if placed under a 50% shade cloth environment. In particular, some heat-tolerant romaine lettuces have shown negative effects from shade cloth coverage.

The same holds true of many heat-loving plants such as eggplant, many pepper species, tomatoes, and other solanaceous plants. While they can still use a little shade during peak summer heat (such as when the temperatures spike over 95 degrees Fahrenheit), these plants often love the 80-90 degree range and thrive in those temperatures, provided they have enough water.

Typically, shade cloth is only beneficial during hot weather. Areas of the country that experience significant heat for months at a time may benefit from shade cloth during the peak heat season, but only if they use shade cloth in the 30-40% range during that peak season. In other seasons, such as the spring or fall, temperatures often drop to the point where shade cloth is no longer required.

Which Shade Cloth Should I Choose?

Shade density level  Areas commonly used in

Crops 

30%

Northern regions

Most cool-weather loving plants, tender perennials, some part-shade annuals. Sometimes used for sun-lovers like tomatoes, peppers, eggplant, squash to prevent sunscald during peak summer.

40%

Most of the United States

Flowering plants, most vegetative crops during peak summer heat.

50%

Deserts or extremely humid, hot regions in zone 10+

Most vegetative crops throughout the summer

60%-90%

To shield humans in extremely hot regions, and may sometimes be used for shade plants

Shade-loving crops and ornamental plants such as orchids and ferns

Many standard crops you plan on growing in your garden this year may benefit from 30%-40% shade cloth. Typically cloth in the 80%-90% range is used to shield people, so, for instance, wrapped around an outdoor seating area, but it has been discovered that they can also be used to help grow shade-loving plants in a sunny region. 

Colored Shade Cloth

It is important to note that each color has a unique impact on crops.

While color spectrums do have an impact on plant development under LED lighting (which is why so many people use red or blue grow lights indoors), sunlight is a full-spectrum light that contains all of the available colors. As a result, while we might think that adding a red or blue shade cloth might increase the red or blue lighting to the plant, this is in error — we’re actually blocking a percentage of all light from reaching the plant.

Shade cloth comes in red, green, blue, yellow, brown, black, or white/off white. These all have different diffusions of the UV rays as mentioned above, but it also can have a dramatic impact on the efficiency of the plant’s water use.

The water use efficiency of sweet peppers while using shade cloth was tested in a 2021 study by the American Society for Horticultural Science. No shade cloth was a control group, and white, green, and black 50% shade cloth were tested. Green enabled the plants to have the highest water use efficiency, followed by black and then white; no shade cloth had the least efficiency. As a result, sweet pepper growth, plant health, and fruit quality increased most under green shade cloth.

Getting Started With Shade Cloth

Before buying a lot of material, conduct a small-scale experiment to ensure that you like the results.

Keep it simple at first. If you are growing vegetables and flowers outdoors in average climates, pick a 40% cloth, black or green, for your peak summer months.

Do your own experimentation on a small scale and make sure you like the results before you invest in a lot of product. 

How to Test 

Try growing two beds of the same crop side by side and covering only one of them with shade cloth.

Grow the same crop in beds next to each other and cover only one of them with shade cloth. Take notes throughout the crop’s life. Pay attention to root length, stem diameter, days to maturity, overall leaf size, regrowth, sun spots, height, harvest size, etc. Then try it again with another crop.

The best research will be done in your own growing space due to additional factors such as humidity, wind, soil, sun exposure, etc. Studies have shown that overall, plant growth increases if used properly. 

Like any tool you are using for the first time, it’s suggested you use shade cloth for the whole hot season to really get a feel for how it affects your crops in your specific region. 

Using Shade Cloth to Transition Your Plants

To ensure proper growth, we begin growing temperature-sensitive crops like tomatoes and peppers indoors using artificial lighting.

We start some of our most temperature-sensitive crops, such as tomatoes and peppers, inside our home and use artificial lighting. We allow them to grow to an appropriate size before bringing them out into our greenhouse. Then, we place them on a metal shelving unit draped with 30% black shade cloth.

Trays newly brought out into the greenhouse live on the shelves for a few days. This helps them to acclimate to real sun versus artificial grow lights. 

On days one through three, we drape two layers of the shade cloth over the shelving unit. This blocks most direct light and keeps the air cool.

This is especially important if the first few days are sunny. We could probably get away with one layer of cloth on a cloudier day.

After a few days of getting used to the new environment, we remove the trays from the shelves. We then place them on the greenhouse tables. This extra yet simple step drastically decreases any stress on the young plants in their new home. 

Final Thoughts

If you live in a growing region where summers are hot, or weather patterns have become a bit more unpredictable, I encourage you to try using shade cloth to offer added protection for your crops. I believe the benefits of healthy and unstressed plants outweigh the possible risks.

The worst that can happen is your crops take just a little while longer to mature due to a bit less sun, which can be offset with a little extra planning. 

Keep in mind, shade cloth is just as easy as removing row cover for frost protection, so you can use it for a few days and then remove it pretty seamlessly. With all the different sizes, light transmission levels, and colors to experiment with, surely there is something for your garden.

Contact us to discuss your requirements of use of green shade net. Our experienced sales team can help you identify the options that best suit your needs.