Summarize:

Keep fresh flower wreaths fresher longer by using a foam base and soaking it in water. You can buy a foam base from a craft store, like Hobby Lobby, depending on your location. Choose a foam base that is about the size you would like your wreath to be. Keep in mind that the wreath will appear larger once the flowers are on it. Fill a basin, like your kitchen sink, with water. The basin should be at least the same thickness as the foam base you are using. About a gallon of water should be enough. Place the base in the water. The base will start to sink as it fills with water. Allow it to sit in the water for one or two minutes. Then, take the foam base out of the water, allow the excess water to fall off, and pat it gently with a towel. If using the kitchen sink as your basis, make sure to clean it thoroughly with soap and water first. Put the stems into the foam base while it is still wet. You will need to stick the stems of the flowers into the foam base so they will soak up water. You can either stick the individual flowers directly in the foam, or wire them first. Wiring them first will make for a tighter hold. To wire them, wrap floral wire around a bundle of stems. Then, put the stems into the foam. It may take some effort to insert the flowers into the foam. Don't use too much force, or you could break the foam. Continue attaching flowers until the wreath is mostly filled. There is no correct design. Fill it in however pleases the eye. You can plan it beforehand before you attach them if you have a specific idea. Tuck in extra flowers, leaves, or other embellishments to complete the wreath. You can use pins or glue to secure flowers if you are having trouble making them stay in position. Spritz with water daily to keep the flowers alive longer, or allow them to dry naturally.
Buy a foam base. Soak the foam in water. Attach the flowers. Fill in the wreath.