As another suggestion in addition to the current answers, a perhaps more productive method to achieve this goal is to complete the requirements to unlock the island. This can be achieved as early as day four (source) and will allow you access to several mini-games that generate temporary locations with flowers already planted. You can pick up these flowers and they will remain in your inventory after the mini-game has ended. You can store the flowers in the box near Leilani, which holds up to 40 items. When you leave the island, you will be able to collect any items in the box located on the dock.
Collecting flowers from the island will allow you to plant new flowers instead of tricking the game counter by planting existing flowers, and to begin any landscaping goals (or progress towards particular badges) earlier. It is a useful source of flowers even after the gardening shop opens, as you can collect many more flowers on the island than you can each day in the shop.