Identifying a deciduous ornamental shrub can seem like a challenging task to the uninitiated. However, the task becomes immensely simpler once you learn what to look for. In order to identify a deciduous ornamental shrub you will need to look at, and take note of any, and all, characteristics that you can identify, no matter how inconsequential they seem. After you have this information, you can consult an online database (See Resources) or a horticultural encyclopedia to make your identification. There are some common characteristics you should look for when you are attempting to identify a shrub.
One of the first characteristics you should look at when identifying an ornamental deciduous shrub is its size and shape. When noting size you do not need to be overly concerned with specifics. Sometimes just a range in feet (or meters) will be helpful. Remember though that the plant may only be in a juvenile state and it may grow many more feet. This is why size, when used as an identifier by itself, is not entirely conclusive. However, when used in combination with other identifying characteristics, size can very well become an important factor. For example, if you believe you have identified the shrub as a sprirea (Spirea japonica) but you noticed that it is only two feet tall and very compact, then chances are you are dealing with a dwarf variety (such as Little Princess or Alpine).
It is important to note the overall shape of the shrub. Is it tall and skinny? Or is it short and wide? Does the plant seem to spread out across the ground? Anything you notice about the size of the plant will be helpful later on. Remember, as with size, the shrub's shape will not generally lead you to a positive identification by itself but it will be helpful when combined with other characteristics. As with size identifiers, shape identifiers can help you distinguish between different cultivars of the same plant. For example, assume you have otherwise identified a plant as Hypericum (St. John's Wort) but it doesn't seem to completely match the picture you have. However, you notice a spreading or trailing shape, as opposed to a compact or upright one. Your identification may be spot on and the difference in shape will help you determine if this specific cultivar is simply a spreading variety.
The leaf is probably the single most important piece of information that you can use to identify a deciduous ornamental shrub. The reason the leaf is so useful is that it contains a whole host of information that can be used in an identification. If possible, grab a small sample of stem that has a couple leaves on it. If taking a sample is not possible, write down anything you notice about the leaf. For instance, you should take note of the leaf's shape, size, colour, and even minute details like how the edges of the leaf look and what the texture of the leaf is. Leaves, especially those from the same species of plant, may seem identical but if you scrutinise them closely you will notice tell tale details that will help distinguish them.
If you are lucky enough to be identifying an ornamental deciduous shrub when it is in bloom, take special note of the flower. Again, if possible, take a flower as a sample which you can reference later on when you are doing your identification. If grabbing a flower is not an option, note the flower's colour, its size, whether or not it is fragrant, and anything else about the flower you notice. For example, suppose you believe you have identified the plant as a viburnum but notice that its flower is white and similar to many other varieties of viburnum. If you do a quick smell test and notice a distinct, almost spicy, fragrance, this well help you to distinguish the plant as a particular kind of viburnum (Korean Sprice).
Remember, even seemingly inconsequential details can be crucial later on so it is important to write them down.
Be careful when handling plants you are unfamiliar with, if you are not careful you can hurt them, or vice-versa.