True story: a few days after I built my first misting beds it rained for two days, and we received about an inch of rain. I went out to look at my beds to see how they fared. They looked great! I had used very course sand for my rooting media because it was very inexpensive and drains extremely well, and my property slopes down to a pond. I walked around the beds and decided to step in to see how soggy the sand was. Dumb move! I sunk up to my knees!
I had built the beds by digging and removing the sod so the grass would not grow up into the sand. When I did that, I created a small bathtub where the water collected. Because the sand could not drain, it turned to something that resembled quicksand. How was I going to fix this, I asked myself.
Because the beds were higher than the pond I knew the water would flow in that direction if I could get the bathtub I had created to drain. I had to move the water 75 feet across my lawn to the pond and knew it would not be easy. My lawn is peppered with rock ranging from fist sized to some that are larger than a microwave! No easy digging, especially if I was to use the round perforated pipe that most people use.
I took a trip to Home Depot and found a product that is used to drain water away from foundations. It is plastic honeycomb wrapped with a fabric that allows water to pass through it. It is about 6″ wide and 1″ thick, and came in 50′ rolls. I purchased two rolls and then decided on a plan. I would take my landscapers spade and jam it in the earth, wiggle it back and forth to create a slot about an inch wide. I did this and created a small ditch from under my mist beds to the pond. I then placed the drainage material into the ditch and covered it over with soil. By the time I was done and had everything run to the pond, the sand was completely drained and I could stand on it!
That drainage material works so good I have used it in two other locations on the lawn that had natural springs bubbling even during the driest periods of summer. The two areas were so bad that every time I tried to mow the grass over them I would sink up to the axles and mud would be sprayed everywhere ! Now that the drainage is installed, I can mow those areas directly after a storm.
The moral of the story is to plan on moving the water away from your misting beds BEFORE you discover you need to. Simply place either perforated pipe or the cloth covered drainage material I mentioned under your sand to carry the water away. Even if you have to cut a hole in the wood of your bed to dump the water onto the surrounding lawn it is better than your sand being saturated.