The best flowers to plant in April are annuals, which are plants that come up from seed, flower and set seed in one growing season. Some flowers re-seed themselves from year to year, so unless you want more plants in a different area you may not need to plant these every year. Cosmos is an example of a flower that may re-seed itself. Plant other flowers such as zinnia and marigold yearly.
Zinnia is one of the best flowers to plant in April. Direct sow seeds of this plant in the garden where you wish them to grow. An alternative to this is to start the seeds indoors five to six weeks before the last frost date for your location.
If you start zinnia seeds indoors, set the young plants outdoors in a protected area for a short amount of time each day so they become accustomed to outdoor weather conditions. The proper term for this procedure is hardening off. Once the zinnia plants are hardened off, plant them into the garden in an area that receives full sun.
Use row cover, a lightweight polyester or polyethylene fabric, to protect both seeds and young zinnia plants from unexpected frost so you can plant them in the garden in April. Use tomato cages or similar wire structures to suspend the row cover above the plants so it does not touch the foliage.
The roots of the marigold help control nematodes in vegetable gardens. The white, orange or yellow flowers can bring a lot of color to the edge of a flowerbed. Marigolds also do well in containers.
One of the best flowers to plant in April, some varieties of marigolds make a wonderful border plant because of their small size. Other varieties of marigolds are better used further back in the flowerbed. Read the packet to see how tall the variety you select will grow. As with zinnia, use row cover to protect both the seeds and young plants when planting marigolds before your last frost date.
Once cosmos establish themselves in your garden, you may find there is not a need to plant them every year. Cosmos often re-seed themselves, even in colder USDA zones where they should behave as an annual. It is best to save seed from year to year just in case they don't come back. Direct sow cosmos seed in the garden.
Cosmos are the best flowers to plant in April because they are not typically affected by light frost. If heavy frost threatens, cover the plants with row cover.