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Sub-irrigated planters (SIPs) will save you time and money. They’ll also help you grow healthier plants than standard garden pots produce.
Do you have a patio or container garden? If you’re using traditional pots, you know that it can take a lot of work to keep the plants in them properly watered and fertilized – especially during the summer.
Growing plants in traditional pots/containers
In the summer, pots are being heated from all sides, as the potting soil inside wicks moisture up and out into the air. In the middle of the summer, the extreme heat makes daily or twice-daily watering a necessity when you’re growing plants in pots.
Meanwhile, your potted plants also require regular applications of liquid fertilizer or slow-release pelleted fertilizers because:
1. Limited space
The plants’ fast growth can only be fueled by whatever nutrition is in the pot. (Unlike in-ground plants whose roots and mycorrhizal partners can constantly grow outward, sourcing nutrition from greater distances.)
2. Nutrient loss
The constant flushes of water through the potting soil quickly washes the fertilizer/nutrients through the potting mix and out of the bottom of the pot. By the end of the growing season, your patio or deck has probably received as much fertilizer as your potted plant has!
Next thing you know, gardening goes from being a fun pastime that puts delicious food on your table to a burdensome chore. You can’t even go on vacation without recruiting a potted plant sitter!
Growing in Sub-Irrigated Planters
Thankfully, there are ways to do container gardening that drastically reduce the time, effort, and resources required.
One of our top recommendations? Use sub-irrigated planters (SIPs).
What is a sub-irrigated planter?
Sub-irrigated planters (SIPs) are planting containers designed so that irrigation is provided by a sub-surface water chamber, wherein water wicks up to the plant’s roots via capillary action (wicking) rather than being irrigated from the surface.
If you want to see the gravity-defying power of wicking, place the bottom of a towel in a bowl of water then come back a little while later. The whole towel will be soaked, despite the downward pressure of gravity.
In case you’re having trouble picturing a SIP, here’s a diagram we sketched showing how SIPs work:
Do SIPs Work?
Now you might be thinking: do SIPs actually work better than conventional pots and containers? The answer: YES!
That’s not just based on our opinion… A 2016 study on wicking bed irrigation (same process utilized by SIPs) conducted on tomatoes by the School of Natural and Built Environments, University of South Australia, found that:
“WBs (Wicking Beds) performed as well or better than precision surface irrigated pots, showing statistically significant improvement in WUE (water use efficiency), yield and fruit quality. The results also suggest an optimum design exists for soil depth (where 300 mm outperformed 600 mm) but not reservoir depth (no difference between 150 and 300 mm). The WBs were more labour efficient, requiring significantly less frequent watering to achieve the same or better WUE. WBs are inherently low-tech and scalable and appear well-suited to a variety of urban agriculture settings.”
Notice that the researchers mentioned “low-tech” in that last sentence. SIPs don’t have to be super fancy and expensive. In fact, many people make their own SIPs, and the internet abounds with DIY sub-irrigated planter guides.
However, if you’d prefer to get more aesthetically attractive, pre-made SIPs, here are a few options that we highly recommend:
Organic Tomato Success Kit
If you want to easily grow your own organic tomatoes, peppers, etc. in a planter, this SIP kit will do it. Includes a self-watering planter, cage supports for your plants, and organic soil mix with all the nutrition and beneficial microorganisms your plants need to stay healthy, well-fed, and productive. Also has a steel trolley (extra) to raise it up.
Sizes: 26″ L x 19 3/4″ W x 10 1/2″ H
Price:
Organic EarthBoxes
EarthBoxes are another great option for growing organic veggies in a small space. We’ve been amazed by some of the patio garden photos sent to us by GrowJourney members who use EarthBoxes to grow everything from large tomatoes, to squash, to corn. Designed to drastically reduce irrigation and make growing organic food on a patio easy.
Size: 29″ L x 14″ W x 11″ H
Price:
Terrazza Trough Planter
This SIP planter is used throughout Italy and is much deeper (16″) than most American planters of a similar style. A dual action watering system that can hold up to 4 gallons of water means you’ll only need to water once or twice a week. You can also get rollers/casters to make it super easy to move around on your deck or patio.
Size: 16 1/2″ W x 39 1/4″ L x 16″ H
Price:
We hope this article was helpful! Have questions about gardening in SIPs or other containers? Ask away in the comments below.
Related articles you’ll want to read:
- Finally! Garden pot sizes decoded
- Ceramic pots vs plastic pots vs fabric pots: which is best?
- Potting soil vs seed starting mix vs garden soil
- Container gardening questions answered (on our sister site, Tyrant Farms)
- Root pouches: a helpful new tool for patio and container gardening (on our sister site, Tyrant Farms)
Sips: I have 5ltr pots for my tomatoes the bottom has some small chippings in then soil/ compost mix. I have stood the pots in a level controlled water trough of about 25mm (1”) of water in my greenhouse. I can adjust the water level if it’s not enough in summer will this work.
PS like your site.
Sounds like a great SIP setup for growing tomatoes, Roger! Keep us posted as the growing season progresses.
Hello! I am hoping you can give me some advice or recommendations on some SIPs I have made this summer. I have created several garden boxes for my deck using SIP information found on various websites. Two of the boxes are 2′ x 8′ x 12″ high. I used three 4′ irrigation pipes in each. The irrigation pipes came covered in a “sock”. I used miraclegro moisture control potting mix. I did not lay down a layer of landscape fabric on top of the pipes because the pipes were already covered with fabric. I am wondering if I have too much water:soil ratio (if possible). I have what looks to be a thin layer of green moss/algae/? growing on the top of the soil. The soil at the surface is continuously moist. Not wet, but definitely moist. I have beets growing in one box and they seem to be doing fine. I have green beans in the other box and they seem to be having some issues that may be related to the roots being too wet. This is my first attempt at SIPs – so I can definitely use any advice or recommendations ;-). Thank you!
Hi Donna! There’s no hard and fast way to make a SIP, so each DIY SIP setup is likely going to be different. However, it does sound like your setup may be creating too much moisture in your potting mix if you have moss/algae growing on the soil surface. In this article, we have a diagram showing how we recommend constructing a SIP, which prevents too much moisture from getting into the soil. Does your setup have an aeration screen or air chamber above the water reservoir, as shown in our diagram? If not, can you maybe provide a bit more of a description of your setup so we can help you figure out how to lower your soil moisture levels?