You need a good potting soil mix with a well balanced nutrient supply.

I haven't used this myself, but am planning to order it soon. It's in Mellenger's catalog...called "Rootblast, root stimulator....micronutrient granules create huge root systems so plants grow bigger, faster, and yield more blooms and vegetables! Use on all seeds, flowers, vegetables, cuttingss, transplants, trees, and grass. Rootblast is friendly to the environment, not petroleum based, and hormone free. Use once per season. No mixing with water. 2.5 lbs. is enough for 150 plants. 2-1-2." Check it out at mellemgers.com. under organic plant food.

That should read Mellingers.

Here is a link that might be useful: Mellinger's catalog