I am looking for information about planting floating emergent plants (e.g., water shield, yellow pond lily) in natural ponds. If planting young plant material in the soil, what is the recommended water depth? Is it okay to submerge the entire shoot? If yes, what is a safe depth from top of shoot to water surface?
There are several different types of plants that are grown in ponds. A great resource on planting floating plants is The Water Gardener’s Bible: A step-by-step guide to building, planting, stocking, and maintaining a backyard water garden by Ben Helm and Kelly Billing (Rodale Inc., 2008). In the book they explain that floating plants will either float on the pond surface or be slightly submerged. The most popular floating plants are Frog’s bit (Hydrocharis morsus-ranae), Water hyacinth (Eichornia crassipes), Water chestnut (Trapa natans), and Water soldier (Pistia stratiotes). They also explain submerged plants that will inhabit a pond at all levels, from those whose roots sit on the bottom to those that emerge from the pond, getting only their feet wet. For planting a water lily, place on a stack of bricks in the position where the lily will be sited, so that the top of the planted basket is no more than 1 inch (3 cm) below the surface. As the leaves start to extend, remove the bricks until the basket is on the pond bottom.
Another great book is Plants for Water Gardens: The Complete Guide to Aquatic Plants by Helen Nash and Steve Stroupe (Sterling, 1998). The book contains a huge list of a variety of lily plants and specifications for planting and survival.
Texas A & M Extension has a website on water gardening with useful information on planting aquatic plants. You may want to check your local list of invasive species before planting.