By the time summer appears, you'd like your garden and landscaping to be full of bright annuals that will last until the first frost. You can purchase ready-to-go flower plants from your local nursery or garden center. However, it can cost you hundreds of dollars to fill your landscaping each year. When you start with seeds indoors, you can have seedlings such as sunflowers, cosmos, marigolds, zinnias, petunias, alyssums and pansies ready for spring planting at a fraction of the cost.
Make a list of the summer flowers you would like to grow in your garden. Once the seeds are purchased, read the manufacturer's information on the back of the packet. Find the germination and seedling planting times. Every flower will be different. Sunflowers can take five to seven days to germinate and are ready to plant outdoors in three to four weeks. Cosmos take five to seven days to germinate and are ready to plant outdoors in four to six weeks. You can plant the summer flower seeds at the same time and plant the seedlings at various outdoor times, as they are ready (see Resources).
Fill small planting containers, such as peat pots, commercial seeding trays, reused food containers or paper cups, with soil, up to half an inch from the top.
Spray some water over the soil and mix it up. Do not over-water the soil, as new seeds do not like a sopping soil, only a moist one.
Poke a hole in the top of each of the containers' soil using the top end of a pencil. The holes should be as deep as the seeds that are to be planted. This will vary according to the type of summer flower seeds and their variety. The manufacturer's suggested seed planting depth will be listed on the back of the seed packet. Larger seeds, generally, are planted deeper than smaller seeds.
Pop a flower seed in each soil hole and cover it with soil. Mark the container as to the name of the flower seed planted. If you don't, it will just be a guessing game when it's time to plant the summer flower seedlings outdoors.
Place all of the seeded containers into a tray. Place a sheet of plastic wrap over the top of the tray, but do not seal it. This will keep the soil warm and hasten germination. Put the tray by a window that receives sunshine during most of the day.
Spray the top of the soil when it begins to dry. Remove the plastic wrap after the seeds germinate (sprout). Continue to spray water on them as the soil dries.
Plant the summer flower seedlings when they are approximately three to four inches tall and the last frost has passed. Take special notice of the need for sunshine or partial shade for each type of flower. Also, notice how far apart they should be planted. This will be listed on the back of the seed packet. Zinnias will be ready to plant in five weeks, but petunias won't be ready for eight to 10 weeks from seeding.
Dig a hole in your outdoor landscaping soil to the depth of the seedling container, but a little larger around. Remove the seedling and its soil from the container and put it in the ground soil.
Push additional soil into the sides of the seedling soil until it is compact. Repeat this process for each seedling as it is ready to be planted outdoors. Give your new summer flower plants a thorough watering.