Sphagnum peat moss is a sterile component of many potting soil mixes. It doesn't harbor diseases or weed seeds like garden soil does. It also helps retain moisture in the soil without becoming soggy, which is beneficial for most annual plants. Due to the sterile nature of the sphagnum moss, other elements must be added to the potting mix to add nutrients for the plants. Creating the right mix of these elements creates a potting medium annuals thrive in.
Mix one part sphagnum moss, one part perlite and one part sterile soil or compost and place it in a plant pot. Water the mix with warm water until it begins to drain freely from the bottom drainage holes in the pot, ensuring the mix is evenly moist throughout.
Plant the annual flower transplants in the sphagnum mix to the same depth they were at in their nursery pots. Space most plants 2 to 4 inches apart, or at half the recommended distance for garden bed planting.
Water the plants immediately after sowing. This collapses air pockets in the soil around the roots and helps to avoid transplant shock.
Water as needed to keep the soil moist. Most annuals require moist but not soggy growing medium to thrive. Water when the surface of the mix begins to feel dry, and add water until it begins to drain from the bottom drainage holes in the container.
Fertilize once a week with a water-soluble fertilizer. Apply at a quarter the rate recommended on the fertilizer label. Alternately, use a slow-release fertilizer, following label instructions for amount and frequency.