Urban Gardening: DIY Sub-Irrigation Planter

Last year we tried a DIY Sub Irrigation Planter (SIP) for the first time. A SIP is a planter system where water is introduced from the bottom of the planter. This allows plants to have a constant source of water, and also saves you, the gardener, from having to water as often. We have an upper deck that gets pretty good light and were interested in a having a few container plants. We had tried cherry tomatoes in the past, but had issues with them splitting in the heat. Especially in the middle of the summer, we’d water the plant in the morning, and by the time we got home from work the soil was completely dried out. This also made it hard to leave for more than a few days, and we didn’t want to be reliant on friends coming by to water for us.

We got a book from Jesse’s brother called Fresh Food From Small Spaces, and this is where we first learned about SIP container gardening. We were intrigued, and Jesse did lots more internet research (he loves to research things) to learn more about how we could apply this ourselves (this is a pretty good site to learn more). You can purchase SIP containers read to go, but I wanted something that was a little more aesthetically pleasing than what is out in the market, and we already had two tall planters my mom had gifted to us (and I really like overcomplicating things). We tried this for the first time last year, and it worked out pretty well. We had more success with the cherry tomatoes than the bell peppers, but that could be for a variety of reasons.

Our planters worked out great to convert to a SIP. The extra height allows enough room in the base for the water reservoir. Dimensions will vary depending on the planter you use, but as a reference, here is what we were working with. Tulip planter (widens at the top): 20”tall, 14” diameter at the top, 9.5” diameter at the base. 2 gallon bucket: 9” tall, 9”diameter.

SUPPLIES 

Planter, bucket/container for the water reservoir, PVC pipe for the fill tube, plastic water bottle for the soil wick, plywood/wood/bucket lid for the platform, landscaping cloth (not mandatory), and a mason jar to fit over the fill tube opening.

1. Find an appropriate planter (my mom purchased ours from Piney Ridge in Johnston, Iowa).

2. Find a bucket/container (the water reservoir) that fits snugly into the bottom of the planter. It still needs to have a little extra space on the sides, so when the reservoir becomes full*, the extra w­ater will spill over the edges, and out the bottom of the planter. Our bucket is made of HDPE (high-density polyethylene) food grade plastic.

*If you can/want to drill holes into your planter, you can drill drainage holes near the top of the water reservoir, and this will allow the extra water to flow out through the openings.

3. The platform piece should fit on top of the bucket/container. We used untreated plywood*. The platform is the same diameter as the bucket. You will need to cut two holes, one the diameter of the water bottle you will use for the wick (placed in the middle), and a smaller hole that is the diameter of the fill tube (off to the side).

*We may try finding a bucket with a lid next year, and using the lid as the platform. This may be more efficient than what we currently have.

4. We purchased a large bottled water to use for the wick (the extra large size). Jesse cut the top off, and drilled several holes into the plastic. It wasn’t quite tall enough to touch the bottom (it should be slightly taller than the bucket), so he added a few pieces of leftover plywood to the bottom. Gradually fill plastic bottle with soil, watering the soil and compacting down the soil as you add more so it is very dense. 

5. Place wick in center hole, make sure top is flush with the platform.

6. Cut the bottom of the PVC pipe (fill tube) at an angle to ensure the water can flow into the bucket. Add fill tube through smaller hole in platform. 

7. Add landscaping fabric*. You won’t need much landscaping fabric, so we asked some friends who were homeowners, and one had lots of extra that he was happy to pass onto us. You can adjust the fabric as you add the soil. If you can, try to keep the fabric above the soil line.

*Not mandatory, but can prevent roots from getting into the water reservoir. We used landscaping fabric last year, and the bell pepper roots still made it around the landscaping fabric and started down the side of the fill tube. I don’t think this affected the peppers at all though.

8. Fill with soil.

9. Place plant into dirt. Place a cover over the fill tube when not in use. A mason jar works well. This does a couple things; it keeps mosquitoes from going into the tube and laying their eggs in the water, and also keeps other stuff from clogging up the tube.

Depending on how much rain you have, and how hot it is will effect how often you need to water. If the dirt is dry, I like to start by watering from the top, so the plant and top soil are wet. Than we fill up the reservoir by pouring water into the fill tube. We continue to fill it with water until we see water pool up in the tray on the bottom. Since we have a 2 gallon container, we also know roughly how much will fill it up (this also allows us to see how much water was soaked up within a period of time). A gallon milk jug works well for this part, since it also lets you measure and track how much you have put in.­­

We’ve figured out a water management system, but now need a pest control system. We made it about half way through last season before the squirrels found our tomatoes (they left the pepper and other plants alone). They have already found the plant this year, and started to eat the leaves of the tomato plant! It really pisses me off, and we are working on a system to keep them out of it. We are trying bird netting, but haven’t quite figured out the logistics yet. If you have any suggestions, let me know!