All sorts of seeds can be sown in rootrainers, but we mainly use them for beans and sweetcorn. Use them to sow seeds early in the year and protect them from frosts. When they frosts come to an end in May you'll be planting vigourous plants, rather than sowing seeds - guaranteeing an early harvest.
The long, ridged cells encourage vigorous root development, and they're narrow enough to fit on a windowsill inside. Each one comes with a waterproof tray.