Jiffy 16 Pellet Tomato & Vegetable Greenhouse, 50mm Pellets. Start up to 16 plants in the Jiffy 16 Pellet Tomato & Vegetable Greenhouse. Featuring our largest peat pellets, they are the perfect size for tomato seedlings and other plants with large, complex root systems. As a bonus, get your seedlings started off strong with a sample of SUPERthrive, a kelp-based vitamin for plants! 16 50mm diameter peat pellets. Base watertight plastic tray. Clear greenhouse humidity dome. Bonus SUPERthrive Plant Vitamin sample and plant markers.