We seem to be a civilization that is constantly catching up, rather than one that is proactive. This can relate to many aspects of our lives, whether it is in our own health and wellness or how we take care of our responsibilities. Trees and plant material are an example that I notice, probably has something to do with being a landscape architect.
We can always tell if a plant is in need of water based on its appearance. Specifically, we see the need in the color of the plant’s foliage. However, not all plants are created equally in this respect. Trees in particular do not show their need for water until they have either become stunted for the rest of their lives, or they slowly die off. A lot of this has to do with the storage capacity of a tree for water. Trees gather and conserve water for use during drought periods so that it can be used when it is not naturally, or manually receiving precipitation. Shrubs, turfgrass, perennials and annuals show their need for water much faster.
This leads to my hypothesis which is: An urban street tree has a greater success rate when it is planted with annuals, perennials or other small plant material than when it is located in isolation.
Owners, passerbys and those who appreciate the landscape will naturally notice the need for water for the low-growing plant material and supply the water to bring it back to it’s living state. The tree, on the other hand, does not have this luxury. The tree does not show its need for water to the degree of the flower, therefore it does not receive supplemental water. The exception to this, is when the tree is provided supplemental irrigation, however even this is not fool-proof.
The sketch above illustrates an elegant urban option where flowers surround the base of the tree. Also notice that rainwater runoff is also accepted for infiltration and natural irrigation with weep holes between the concrete walk and low border.