If you have an inground garden, just choose a day when your garden is looking attractive. An overcast day will give you the best results as bright sunlight bleaches colours out. Then take your photos.
If you have a container garden you have an extra challenge as most, if not all, of your plants are probably annuals. We have deliberately provided a long entry period to allow your plantings time to become established before you take your photos, so we suggest you time your entry towards the end of the month. Don't worry if your display is not at its best – all entrants are in the same situation.