Rootrainers Rapid Rootrainers - 3 Inches Deep, 32 Count, Black Greatest and most convenient root training system out there Unique design allows air pruning for optimum root formation - and better roots mean better plants every time Grooved cell design directs main root to grow straight down towards the large drainage opening at the bottom Cells open for easy removal of plugs and damage-free roots Reusable from year to year and includes detailed instructions and planting tips