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Sub-Irrigating Planter (SIP)

A sub-irrigating planter can be made from a plastic tote, a 5 gallon plastic bucket, or a design of your own using wood to build the planter. As long as you have a water reservoir below the soil, some way to fill the reservoir, and some way to wick the water up into the soil, the SIP can take on any form depending on your creativity and the materials that you have available. Check out Alternatives and the Rooftop Gardens Project in Montreal for more information on the subject, including ways to connect many sub-irrigating planters together: www.alternatives.ca / www.rooftopgardens.ca

The following instructions outline my design using a plastic storage tote from Home Depot and 3" plastic hydroponic baskets ordered from amazon.

Materials:
- 18 gallon/68 L plastic storage tote
- 16" piece of 4" thick PVC (for support base)*
- 2' piece of 1.5" thick PVC (for watering spout and centre support)
- 3" hydroponic baskets**
- zip ties

*there will be one support in each corner of the tote to hold up the base for the soil. You could use 4 glass jars of the same size, bricks, or anything else that can safely rest in the water reservoir and that's sturdy enough to support the weight of the soil. 

**you could use any recycled plastic container that you can cut vertical slats into, such as sour cream or yogurt containers, 2L pop bottles, etc.

Tools:
- sharpie marker
- tin snips (a razor knife will work, but it's sloppier and not as safe)
- hack saw
- measuring tape
- drill
- knife

Method:

1. Determine the appropriate levels for the water reservoir and the base of the soil substrate. 

Markings on inside of container and drill holes
This will depend on the height and volume of your container and what you plan on growing. Measure from the bottom of the container and mark the water level and the soil base level with a sharpie. Do this on all four sides and then drill a hole just above the water level. My 18 gallon plastic rubbermaid tote is around 15" tall and I went with the following spacing: 

3.25" water
0.75" air between water and soil base
soil base starting at 4"
8-9" soil substrate
2-3" mulch

2. Cut holes in the lid for wicking mechanisms and drill holes for air.

Wicking baskets and their four holes evenly spaced on soil base.
Place the lid on the container and determine the spacing of your wicking mechanisms, remembering that some areas (in my design, the four corners) will be occupied by supports for the soil base. Around 10-15% of the lid (or flat area for the soil) should be devoted to the wicking mechanisms that will rest in the water. Distribute them evenly and then trace a circle. If using hydro baskets, draw another smaller circle inside this outer circle to accommodate the width of the lip. If using plastic containers or pop bottles with no lip, you'll be using zip ties instead to secure them to the soil base. Cut into the centre of the circle with a knife and then use tin snips to cut out the plastic.

3. Cut PVC to length. 

Four 4" PVC pieces to support soil base. One with water spout attached.
Using a hack saw, cut the 16" piece of 4" wide PVC into four 4" pieces. Cut off a 4" piece of 1.5" PVC to use as an extra support for centre of the soil base. The remaining 20" piece will be the water filling spout. 

4. Attach the centre support for soil base.

Bottom of soil base with centre support.
Drill a hole in the exact centre of the lid. Place the small piece of 1.5" PVC over the hole and trace a circle. With the sharpie, make three marks on the bottom of the PVC near the lid and three corresponding marks on the lid. Use a knife to twist a hole into each mark and then attach the PVC to the lid using zip ties. 

5. Cut out the inner part of the lid to act as a base for the soil substrate.

Cut the inner part of the lid a little bit bigger and whittle it down to fit snug.
Measure the length and width of the inside of the container at the 4" mark, which will be where the plastic will lay on top of the soil base supports. Place the lid back on the tote and place markings on all four sides. Trace a line around the perimeter of the lid, taking into consideration the unique shape of your container, and also leaving about 1/8  of an inch extra (it's better to cut too big the first time rather than too small). Start the cut with a knife and then cut all the way around with the tin snips. Place the soil base into the container and wherever it's too wide cut back a little bit at a time until it rests evenly on the supports and snug against all four sides of the container.

6. Attach the water spout.


Cut out a 2" deep, 1.5" wide section of one of the soil base support PVCs and attach the water spout PVC to it using zip ties. This will help to keep it in place. Cut out a small section of the soil base (plastic lid) to make room for the water spout. The water spout should rise 3-4" above the top of the container to allow for easy filling.

7. Fill your container with soil substrate and water. 

Fill wicking mechanisms with pure peat or coir.
The rest with mixed growing medium.
Do this at least a week or two before planting or transplanting into the container. When soil is settling it looks like tiny earthquakes under microscope, which can be a significant stressor for the tender roots of young transplants. Use a substrate that is primarily peat moss or coconut coir (best wicking effect and light weight). Pack the wicking mechanisms tightly (but not too compact) with pure peat or coir and then fill the rest of the container with your growing medium (soil, peat, coir, compost, perlite, etc), allowing a few inches at the top for mulch. For the first few days the water reservoir will deplete rapidly, and you'll have to add water a few times a day. Eventually the soil and water will reach a point of equilibrium and the entire container should be evenly moist. Pour water slowly into the spout until it starts to dribble out of the overflow hole.





















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