Here is a portable micro garden (aka sub-irrigated planter - SIP) made from recycled plastics installed in a mortar box.
The same method works in any watertight container including a traditional raised bed lined with sheet plastic. It is a universal method.
This is one sure way to avoid the hazard of often-contaminated city soil. The bonus is increased productivity in the range of 50% more vegetables per square foot vs. in-ground growing while saving up to 90% of the water.
The recycled plastic containers create water and oxygen reservoirs. The front row is an inverted nursery flat, the second is a row of strawberry containers and the third (blue containers) held mushrooms. Note that there are aeration holes drilled (or use a hot poker) in the tops of the reservoirs.
The fill tube (upper left) is a water bottle with the bottom cut off. Note that there is no need for connection pipes between the reservoirs. The bottom of the planter acts as the connection "pipe". Water will flow and fill each reservoir.
The soil in the spaces between the recycled containers forms a wicking system. The photo shows the planter only partially filled for demonstration purposes. It is now ready for filling to the top with soil mix and planting of either seeds or starter plants.
A key element is the overflow drain hole. The plastic tube at the front goes through the container sidewall into the nursery flat at the highest point as you can see. As the water rises by capillary action, air pockets are formed at the tops of the reservoirs. This gives the plants a valuable reservoir of oxygen. These oxygen reservoirs coupled with the overflow drain hole prevent over watering.
These planters are very simple to use. A child can water it. Simply add water through the fill tube until a small amount exits the overflow drain hole. This indicates that all of the reservoirs are full and that the water level is no higher than the height of the overflow drain hole.
All sorts of recycled food containers can be upcycled in this way. Recycled ½ gallon milk containers or juice bottles would work just as well. Can you think of a better way to recycle plastic containers than to use them to grow fresh food in the crowded city?
This post shows a way to make SIPs like this using perforated corrugated drain pipe.