Zinnias are one of the easiest annuals to grow, grow quickly, and bloom heavily. They make a massive burst of color in your garden. Zinnias have bright, solitary, daisy-like flowerheads on a single, erect stem. Plant them in full sun. Zinnias are adaptable but prefer fertile, humus-rich, well drained soil. If the soil is amended with compost, the flowers will grow more quickly. Deadhead to prolong flowering. Maintain moderate soil moisture and fertilize lightly.