Step 1 - Measure 3 1/2" from bottom of a 22 1/2" Plastic Whiskey Barrel (Home Depot) and drill a 7/8" hole at 3.5" from the bottom for the 1/2" PVC pipe overflow. The elbow connector is glued to the outside to shoot overflow down (less messy). I use a straight connector glued to the inside to hold the PVC Overflow connector in place. If you don’t want to make a PVC overflow simplydrill 1 or more 3/8" holes from the bottom for drainage.
Step 2 - Cut a 5 gallon bucket bottom off at the bottom 3 1/2" to make a support base. Cut about a 6" diameter hole in the center of the bottom, drill 3/8" holes on top and the sides for sides for irrigation then make 3 - 4 cuts at the lip that will allow water to flow through this platform when it is inverted. Place the support platform in the center of the whiskey barrel bottom end up.
Step 3 - Cut your 20 gallon plastic container bottom off at the indentation to make your platform (holds the potting mix up in place). Cut about a 6" hole in the center and drill 3/8" holes all over it for aeration and drainage. You will need to cut a hole for the PVC pipe watering hole. I use 3'4" PVC pipe so I drilled a 1 1/8" hole near one edge for this.
Step 4 - Take a 6" plastic pot (Home Depot) and drill 3/8" holes in it to work as your wicker system and insert in the 6" diameter hole you cut in the support platform.
Step 5 - Drill (2) 1/4" holes the side near the top you insert plastic zip ties into to hold the PVC pipe from being moved. Cut a 20" piece of 3/4" PVC and cut off a piece at the bottom lip (taper it) so it doesn’t sit flush restricting watering from flowing into the base. Insert PVC pipe (taper end down) into your hole your drilled in the support platform and secure the PVC pipe with a plastic zip tie.
Step 6 - Cut half of a 7ft x 7ft (approximate) burlap sack and line this on top of your SIP that will preventing potting mix from entering your wicker system and roots from growing into your aeration and drainage holes making it easier to remove the tree from the container when root pruning. Trim your burlap sack so it doesn’t drag on the ground.
Step 7 - Wet your potting mix and whatever nutrients (Lime, Mycorrhizal Fungi etc.) you want to add every time you set your tree up till the next root pruning and set your tree up centered in the SIP.
Step 8 - Place your 4 mil thick plastic tarp over the top and secure it with either connected plastic zip ties or other cord material. Tighten and trim the ends of the zip ties off and any extra plastic tarp hanging off more than 6" from where it is secured.
Step 9 - Cut a full size 7ft x 7ft burlap sack half way down the middle to place over your SIP and secure it with a clamp and trim as needed. This protects your plastic whiskey barrel from degrading faster from the heat and protects the trees roots when reaching the outside of the SIP from being burned up in the extreme heat of places like zone 9 and 10.
Step 10 - Water and fertilize when called for! You can use a slow release fertilizer. People in Zone 6 can fertilize like that once a year with this system but in my hotter zone (9) I get a longer growing season so I might fertilize like that twice a year like that in Feb/March and then again in June/July. I prefer to use water soluble fertilizers like Miracle grow to start working faster and stop working faster. I might use just MG the first year to get the tree to leaf out. After that I would use 2 parts MG to 1 part Super Bloom that would yield a 7 - 7 - 5 ratio increasing phosphorous without having to worry about bone meal or superphosphate. You can adjust your own ratio obviously.
22 1/2 " Plastic Whiskey Barrel (Home Depot) Container Cost $20
Support Stand (5 Gallon Bucket cut and drilled) $3
Support Platform Plastic 22" inch rope handle tub (cut and drilled) $8 or $9
1 ft piece of 3/4" PVC Watering Pipe $1
1/2 7ft x 7ft Burlap Sack (place over support platform to keep roots from going through holes) $3
1 Burlap Sack (7ft x 7ft) top cover protecting roots from burning in summer $6 (Home Depot)
Clamp for top cover $1 (Home Depot)
plastic Zip Ties $1 (guesstimate)
4 mm Thick Plastic Tarp Cover $1 (guesstimate) worth (but you have to buy a roll)
6" Plastic Container used a wicker $1 + (Home Depot)
* Optional PVC Overflow $5? - 1/2" PVC cut 1 7/8" in length connecting a 3/4" elbow (spout) and 3/4" straight connector (inside the SIP) glued together
Estimated Container Cost $44 plus tax without the overflow piece maybe $50 with it.