I've done the tiered beds and the one single disadvantage was
water. The top
tier could get bone dry in a hurry.
That's why I asked Bev about rooting medium and water. As I mentioned
earlier, the higher garden bed walls go, the more perfect the
drainage and the more difficult it is to keep elevated soil moist. I
only know two solutions: 1] have very-high-ratio organic matter soil;
2] have a built-in watering system that is either on a timer or
constant drip that keeps putting water into that top area.
Lugging hoses sucks. I am working toward a system that takes care of
watering needs whether I get out of bed or not. I have succeeded in
doing this here at the Phoenix property, so I know I can do it at
Heartwood.