Seedling Soil and Peat Pellets
Soil can also dry out rapidly and harm delicate seedlings; for this reason, it is best to use a soil-less recipe that is light and fluffy with a fine even texture and should hold water without becoming soggy. Overly wet conditions can rot seeds and encourage fungal diseases such as damping off. Starting soil should not be too high in nutrients, which could harm the delicate growing embryo. Compost can be used as a base since it slowly releases nutrients to feed seedlings as they grow.
Although it may be tempting to plant seeds shallowly, it is essential to follow the recommended planting depth, so they emerge sooner. Planting too shallow can result in insufficient soil moisture for germination or a weak root system. On the other hand, planting seeds too deeply causes them to use all of their stored energy before reaching the soil surface.
Like temperature and moisture, ideal planting depth varies by plant species. As a general rule of thumb, larger seeds can be planted deeper because they contain more stored energy to reach the soil surface than smaller seeds.
However, some seeds like carrots & some lettuce varieties need light to germinate. The stimulus of light causes them to break dormancy and start germination once exposed to water and proper warmth. These seeds germinate best when planted on the soil surface or just barely covered with soil.
Peat pellets are made from compressed soil that expands when you add water and come in two sizes, 1 inch and 3 inches. The 3-inch pellets are large enough to accommodate the growing seedlings during the 4 to a 6-week growing period when they are ready for planting in the raised bed garden. The smaller one-inch pellets may need to be placed in a larger container to provide them with more time to grow and develop.
I also occasionally use seed trays filled with seedling soil, in which I also grow seeds. Growlight boxes also make it easier to control the micro-environment, particularly the water requirements for germination of seeds and the light conditions for growing seedlings.