Shade Cloth for Cannabis: When to Use It and How Much Shade
Shade cloth helps outdoor cannabis through extreme heat by cutting the sunlight that reaches the canopy. A Maryland vegetable trial used 30% black shade cloth during the hottest weeks. Hang the cloth on hoops or a frame above the plants, never on them. Keep the sides open for airflow, and take it down when the heat passes.
When Does Cannabis Need Shade Cloth?
Cannabis loves sun. Shade cloth earns its place during stretches of extreme heat. For signs of heat stress, see the effects of environmental stress.
Our guide to sunlight and cannabis plants explains how much light plants really use. Growing in different climates covers how hot regions change the plan. Our guide to wind burn is worth a read too.
Shade cloth is a short-term tool for stretches of extreme heat, not a permanent roof.
What Shade Percentage Should You Use?
The percentage is the share of sunlight the cloth blocks, as rated by the manufacturer. A 30% cloth lets about 70% of the light through.
The vegetable research points to light shading:
- University of Maryland Extension vegetable specialist Jerry Brust reports that 30% black shade cloth increased marketable tomato and pepper fruit in Maryland trials.
- The University of Delaware’s Weekly Crop Update notes that shade netting “is commonly used at the 20-30% shade levels.” It also found that 30% black shade from early June to early August improved bell pepper yield and quality, and that shade cloth cut soil temperature by about 5 °F.
- K-State Research and Extension suggests 30% to 50% for cool-season crops carried through summer.
These are vegetable results, not cannabis trials. For a sun-loving plant like cannabis, the light end of that range makes sense. Start around 30% and only go heavier if the heat is severe.
Black, White or Aluminized: Which Color Works Best?
Black cloth was the color used in the Maryland and Delaware trials. White and aluminized (reflective) cloth are also sold, and the Delaware overview notes they may offer additional cooling. The Delaware shadecloth overview describes the main types. You will also see red cloth. It is simply another colored option, and you can choose it the same way as the others, by shade percentage.
How Do You Hang Shade Cloth Over Plants?
Never lay the cloth on the plants. K-State notes it can break limbs or smother plants. K-State recommends resting the cloth on a support structure such as low-tunnel hoops. Taller plants need a taller frame, such as metal poles with wire.
- Leave the ends and sides open so air moves freely. Still, humid air under a cover invites disease.
- Hold the edges down with bricks or sandbags. K-State notes that landscape staples can tear the fabric.
If you grow under cover, our page on greenhouse growing covers shading and venting a structure.
When Should You Take Shade Cloth Down?
Once the heat breaks and daytime highs settle back to normal, roll the cloth up. Plants grow best in full sun the rest of the time. Many growers leave the hoops in place and keep the cloth rolled along the top, ready for the next hot spell.
FAQ
Will shade cloth lower yield?
There is no cannabis trial data to answer that directly. In vegetable trials, light shading at 30% during the hottest weeks improved marketable tomato and pepper harvests. Heavy, constant shade cuts the light plants need, so use it only when heat is extreme.
Is 50% shade too much?
There is no cannabis trial data. In vegetable trials, 30% black cloth improved tomato and pepper results, and Delaware notes 20 to 30% is the common range. K-State's 30% to 50% is for cool-season crops. Start around 30% and only go heavier if the heat is severe.
Can you leave shade cloth up all season?
It is better not to. Cannabis grows best in full sun, and heavy, constant shade cuts the light plants need. Put the cloth up for extreme heat, then roll it along the top of the hoops, ready for the next hot spell.
Shade cloth vs row cover: what's the difference?
Shade cloth blocks a set share of sunlight to reduce heat. A 30% cloth, for example, lets about 70% of the light through. Row cover is a light fabric used mainly to keep out insects or hold in warmth, and it sits much closer to the plants.
