Seed Starting and Indoor Containers Growing Kit. Not all 5-inch pots and 10x20 tray kits are created equal. This heavy-duty kit will save you countless headaches in the greenhouse! This kit includes eight 5-inch pots, a 1020 tray, and a carrying tray insert for easy stability and spacing. All are made from heavy-duty plastic made to last year after year. The inserts hug the pots and prevent them from tipping over. The 5-inch pots are a go-to size for starting seeds intended for indoor growing, potting up seedlings, nursery growing, and prepping transplants for the garden.