Seaweed Foliar Spray
The product you are referring to is a seaweed foliar spray. The active ingredient, kelp, can grow a foot a day and the same hormones that prompt this rapid growth can have a more subtle but similar effect when sprayed on plants in our gardens. Applied directly onto the foliage, the spray seems to promote faster, stronger stem and leaf growth.
When added to the soil at the base of a plant the same hormones can also stimulate root growth. This also seems to help reduce transplantation shock for young seedlings and newly planted bare root stock.
You should be able to find kelp foliar spray at your local garden center. If you cannot find it there, try Gardens Alive. They carry a product called Sea-Rich Foliar Spray.