If you cut off the protruding edge of the barrel top it will slide right inside the bottom half leaving
enough space for about 10 or so gallons of
water. A reciprocating saw makes this a quick job.
Drill a water overflow hole only after the soil is in and the two halves have settled down as far as they'll go.
I used actual wicking matt from a seed starting kit but it is expensive.
Styrofoam under the landscape fabric so soil doesn't plug the drain holes.
Ready to fill in this pic, I spread out the cloth through the soil as its filled.
I've since added rope handles so I can drag it indoors over the winter to keep my bay laurel bush alive.
Fresh bay leaves since 2011!
The black pipe on the right is the fill pipe. The left one (hidden by the cloth strips) has a styrofoam "stick" inside as a water level gauge.