Second mistake: manage the realization of the garden without a project
The garden must reflect our tastes, it has to harmonize with our home, it should not require too much work or too high management costs, and finally should push us to spend more time outdoors.
To have all this you need a reasoned and shared project between designer and client.
The garden design must show its appearance with views and renderings, must illustrate all the proposed plants, must include the direction of the works and must provide for future management.
Without a project you face the realization cost of the garden without having a clear idea of the final result, nor the total costs of realization and management.
So: do not proceed with the realization of the garden without a clear, exhaustive project that satisfies us in all its parts.