Shade Cloth: Does it Actually Work in the Garden?
Are you thinking of using shade cloth, but aren't sure if there's a true benefit to utilizing it in your garden? In this article, gardening expert Jenna Rich examines all you need to know about shade cloth use, including benefits and drawbacks.
Contents
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 range from 30% to 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 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 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.
What Does Shade Cloth Do?
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.
Along with other forms of UV, shade cloth blocks harmful Ultraviolet-B Radiation (UVB radiation). The National Cancer Institute defines UVB radiation as:
“Invisible rays are part of the energy that comes from the sun. UVB radiation causes sunburn, darkening and thickening of the outer layer of the skin, and melanoma and other types of skin cancer. It may also cause problems with the eyes and the immune system.”
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 directly reaching the plants. 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
Most often, you’ll see that shade cloth comes 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. This is a bit heavier and will help hold in the heat from the sun.
Black vs. White Cloth
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. A heat layer will form 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 block more 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 excel is in their refraction rate. White or yellow shade cloth bounces 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, selecting lighter-colored shade cloth for areas where you plan to spend the most time makes sense, simply because you’re more likely to be up in that warm patch by the cloth itself when standing up or moving around. 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, and there are times when it can actually be detrimental.
Breeders typically develop heat-tolerant plants to thrive in 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°F/35°C), these plants often love the 80°F to 90°F (27-32°C) range and thrive in those temperatures, provided they have enough water.
Typically, shade cloth only benefits plants 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 cloth in the 30%-40% range during that peak season. In other seasons, such as 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. Cloth in the 80%-90% range is typically used to shield people (for instance, wrapped around an outdoor seating area), but growers have also discovered that it can help grow shade-loving plants in a sunny region.
Colored Shade Cloth
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 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 color can also have a dramatic impact on the efficiency of the plant’s water use.
The American Society for Horticultural Science tested the water use efficiency of sweet peppers under shade cloth in a 2021 study. No shade cloth served as a control group, and researchers tested white, green, and black 50% shade cloth. Green enabled the plants to achieve 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
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
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 come from your own growing space due to additional factors such as humidity, wind, soil, sun exposure, etc. Studies have shown that overall, plant growth increases when growers use shade cloth properly.
Like any tool you are using for the first time, 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
We start some of our most temperature-sensitive crops, such as tomatoes and peppers, inside our home using 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 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 and place them on the greenhouse tables. This extra yet simple step drastically decreases any stress on the young plants in their new home.
