Fill the seed-starting tray almost to the top with sterile potting soil. Do not reuse potting soil or seed-starting trays when you are starting hosta plants. This is because there may be pathogens in the soil and on the tray that may harm the new hosta plants.
Plant the hosta seeds on the top of the potting soil in the seed-starting tray. Due to the irregular germination of many hosta varieties, you must sprinkle the hosta seeds in a thick layer on the top of the soil. As few as one out of every five hosta seeds will probably germinate. Cover the hosta seeds with 1/4-inch of potting soil.
Spray the surface of the soil lightly with the spray bottle. Place the dome lid over the seed-starting tray.
Place the seed-starting tray in a location where the temperature is between 60 and 70 degrees Fahrenheit. Spray the surface of the soil daily with the spray bottle.
Watch for the hosta seeds to sprout. Move the seed-starting tray to beneath the grow light after the seeds sprout, and remove the dome lid. Keep the grow light on continuously. Continue to spray the seedlings daily with the spray bottle.
Harden off the seedlings when the outside temperature stays above 50 degrees Fahrenheit. Place the seed-starting tray outside in the afternoon in a sheltered location. Keep the seed-starting tray outdoors for 3 hours the first day and gradually lengthen the time outside over the course of 1 week. Move the seedlings to a location where they will receive some morning sun after several days also. At the end of 1 week, the seedlings will be ready for outside planting.
Transplant the hosta seedlings outside. Prepare the planting area by working the soil with the garden spade down to a depth of approximately 6 inches. Add a 2-inch layer of compost and work this in with the garden spade. Dig holes for the hosta plants, spacing large hosta plants 3 feet apart, medium hosta plants 2 feet apart and small hosta plants 1 foot apart. Place the hosta seedlings into the prepared holes and fill the soil back in around the roots. Water the newly transplanted hosta seedlings generously.
Add 1/4-inch of sand around the base of the hosta plants to minimize mildew.
Water the hosta plants by saturating the roots at the soil level. Do not get the foliage wet when you water. Provide approximately 1 inch of water each week. Fertilize by mixing the fertilizer with water according to package recommendations for the size of your growing area. Fertilize after the new hosta plants have grown a third leaf.
Cut off the hosta foliage in the fall after the first frost.