Hey @David Smith I'm still fairly new to microgreens, but in my experience a 14# paving stone works just fine (assuming you are using 10x20 trays). There are some specialty crops that are more nuanced in their weight requirements, but most of your common microgreen crops (like broccoli, kale, radish, peas, etc) will do fine with that much weight. Some of the other more experienced growers will have to speak to the requirements of the specialty crops as I don't have experience with them yet. I currently can't justify using an entire 10x20 tray for most grows as I'm still building up a customer base, so when growing in smaller trays I reduce the weight in proportion to the size of the tray I'm using, like so: 10x20 @ 14# 10x10 @10# 5x5 @ 5#