While flowers can be planted from both seed and from bulbs, annual flowers planted in the spring or early summer of each year are often pre-started seedlings that are already rooted in potting soil. Flower seedlings can be bought in many locations online.
Go to a website that sells pre-started plants. Burpee and Nature Hills Nursery are two websites that sell flower seedlings in individual pots or multi-seedling trays.
Choose the flowers option on the main page. Burpee's flower options include annual and perennial flowers and are listed at the top of the main page of the Burpee site. Nature Hills Nursery has a list of perennials flowers and a list of annual flowers right on the main page.
Select the flower that you want to buy from the flower list and you will be transferred to that individual flower page. Nature Hills Nursery has pre-started plants only and Burpee offers a choice of either plant or seed on the flower page.
Type in the quantity that you would like to buy of the flower and click the "Add to Cart" button to add the flower to your purchase list. Be sure to type the number into the plant box on Burpee and not the seed box. Once you have added the correct number of a specific flower to your cart, go back through the same process to add additional flower types to the cart.
Press the "Proceed to Checkout" button on Nature Hills Nursery or the "Checkout" button on Burpee to get to the checkout. Both sites require registration in order to make a purchase, during which you will create a username, a password and enter your contact information.
Enter your payment information. After registering, you will be asked to enter a form of payment to continue checking out. You will need a credit card to buy flowers for planting online.
Confirm the payment information and your ship to address and your payment will be processed. The flowers will be shipped directly to you.