Answer: Good drainage is important to plant health so improving the drainage is extremely important. Since the bed is already planted you may be able to improve the drainage by repeatedly driving a metal stake 12-18" into the soil to create channels for the water to drain below the layer of caliche. Simply poke the metal rod into the soil as far as you can, every 8-10 inches all over the flower bed. This process will have to be repeated a couple of times during the growing season.
Or, you can dig out the existing plants and rototil the area, incorporating lots of organic matter to help loosen the soil. Till at least 12-18 inches deep so the roots of your shrubs and perennials will have nice, loose soil in which to grow.
Best wishes with your garden!
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