A mesh is not a roof. Rain goes straight through the weave, and you can prove that in a second. Hold a piece up against a bright sky and look at the open gaps between the threads. Light passes through them, and so does the water that falls on your bed. Rain through shade cloth is not the part to worry about. The real question is whether enough water reaches the root zone. Fabric stretched tight over a bed can shed part of a shower off its low corner before a drop lands on the soil.
The fabric is a knitted or woven polyethylene or polypropylene mesh, and it earns its rating from the share of sunlight it blocks. Nothing in that build seals your bed. Threads cross, air moves between them, and water takes the same route. A shade cloth mesh filters light rather than blocking it, which is the point of the material. Knitted fabric gives a little under tension, and woven fabric holds a stiffer grid. Rain comes through both as scattered drips rather than an even sheet, so what you see under a panel is a patchy soaking.
Where you put the cloth changes what the bed gets. A panel pitched on a frame sheds water toward its low side the way a tent fly does, so the row under that edge can catch more of it than the far row does. A flat panel that sags in the middle gathers a pool and dumps it in one spot. Pull the fabric tight, or give it a slope that runs off the end of the bed rather than over the middle of it.
Watering under shade cloth is where growers get tripped up. K-State Research and Extension calls the cover a temporary one and says to remove it for watering and harvesting. You will see why the first time you try to run a hose under a taut panel. Some of the spray beads on top of the fabric and runs to the edge. Lift the cloth, water the soil, put it back. A drip line or soaker hose under the fabric works too, since it puts the water at the surface and skips the mesh.
Rain that does land under your cover does more than fill the soil. Well-watered soil runs cooler than dry soil, so the water and the shade work on the same problem from two directions. Your plants cool themselves by evaporating water from their leaves. A plant short on water closes its stomates to avoid wilting, and it loses that cooling at the moment it needs it most. The cloth drops both the soil temperature and the air temperature around the crop, and it still cannot replace what the leaves give off.
The cover has a cost too. Air that stops moving under the cloth raises the humidity around the leaves and promotes disease. A shower makes it worse, since your wet foliage then sits in still, damp air. Open the sides. Leave a gap at the bottom, or lift a corner after a storm so your canopy dries. Black plastic mulch pushes soil temperature the wrong way, so it has no place in a bed you are trying to cool down.
Check the soil by hand instead of trusting the sky. Push a finger past the surface crust after a shower and feel whether the water went anywhere. A light rain can darken the top of your bed and leave dry soil 1 inch (2.5 cm) down. None of the extension sources here put a number on how much rain passes through the mesh, so treat any figure you see quoted as a guess. Your finger settles it in five seconds, and the answer shifts with the fabric and with how hard it rained.
Read the full article: Shade Cloth: Why Less Shade Grows More
