Petunias, zinnias and marigolds are among the most popular annuals for summer gardens. They can be started from seeds but the seeds should not be planted outdoors until the ground is thoroughly warm. This also goes for celosia (cockscomb), sunflower, morning glory, portulaca and periwinkle. Even if the seeds germinate, the plants may be stunted by cool weather.
Organic materials such as compost, sphagnum peat or decayed leaves should be mixed thoroughly with the soil before planting. Little soil preparation is necessary for those planted in bulb or shrub beds. Still, a light cultivation along with some additional organic matter often helps establish annuals.
Seeds do not always sprout, usually because they were planted too deep or lacked moisture. Directions for depth of planting will be on the seed packet.
Very small seeds that should be merely dusted on the soil are particularly hard to keep moist because the soil surface dries so quickly. Sprinkling them lightly two or three times a day will take care of it.
Too much water is as bad as too little because the soil become waterlogged. A moist surface over dry soil encourages germination and the roots die when they fail to find moisture.
A large percentage of small-seed species require both moisture and a small amount of red light in order to start germination. Such requirements also suit most weeds, which invade disturbed soil.
Light requirement is common in most small seeds rather than larger ones. The red wavelengths necessary for germination can penetrate about one inch of sandy soil, and less then half of that with ordinary garden soil.
Seeds that will germinate in either light or darkness include rinnia, wall flower, gloriosa daisy, alyssum, aster, candyturf and cockscomb.