Sub Irrigated Planters for the Garden

There is limited space in the garden. Some areas were not originally excavated with a back-hoe and cannot be used for planting.

In 2013, Tim Colson (email) read an article in Mary Jane magazine about building sub-irrigated planters from galvanized steel horse troughs. The advantage of this type of planter is less water use and ability to be setup anywhere. After talking it over with some of the community gardeners and parents, Tim proposed a grant to the FFO which was funded.

SIP_angleThe planters went into use fall of 2014-2015! The 5th grade classes are using them and Tim is working with the teachers to come up with ideas for learning science and math skills.

Pictured on the right is a planter before being filled with soil mixture. On the bottom are sections of 4″ drain pipe, cut to support a perforated plastic base. The base will elevate the soil above the water reservoir so the plant roots can breath, and not drown in the monsoon rains.

There will be five soil feet that will bring water up into the soil mixture through capillary action. On the right is a fill tube tube that can be used to add ~40-50 gallons of water to feed the plants and hopefully regulate the heat.

On the right bottom side, is a small black pipe, which is the over-flow to prevent getting too much water when we do have rain.

The soil mixture will consist of compost for nutrients, vermiculite for water retention, perlite for aeration, and Coco Peat as a main anchor in the pot.

The coco peat, supplied by EcoGro in Tucson, is ground husks of coconuts washed in fresh water to reduce salts and compressed into blocks that expand with water to 2.2 cubic feet. The coco peat is more sustainable and absorbs moisture more readily than peat moss which is hydrophobic when it dries out.

IMG_7019There will be three 2x2x6 feet planters in the garden.

Look for them and soon, plus an automatic gravity-fed watering system to feed them from the water harvesting tanks!

Update 2014-Sep-24 : Arbico Organics stopped selling their wasp-compost today, due to massive amounts of rain in Catalina that has soaked the pile. They expect it to dry out in 10-30 days.

2014-Sep-28 : Tim mixed up the first batch of soil! It wasn’t as easy as expected, taking a couple of hours to hydrate three blocks of coco-peat, wet down and add perlite, vermiculite, and ~7 CU FT of  Tank’s compost, plus 2 cups of organic fertilizer (5-3-2.5), and then mix together.


2014-Dec : Of the three planters, we made two with compost and different levels of fertilizer, and the third with a steer manure compost blend. The two with coir and compost are doing pretty good, but the steer manure is barren. My theory is the nitrogen was way too high and “burnt” the plants.

We have a soil test kit, so we will see what that tells us, hopefully before winter break!






For comparison, I also have two planters at home. They are doing wonderfully and we have been harvesting succulent radishes and leafy lettuce for about two weeks now.



  • Mary Janes Farm – original source of the article (not be available online at this time)
  • EcoGro Aquaponics – Tucson local source of Coco Peat blocks
  • Tank’s Green Stuff – Tucson local source of compost
  • Arbico Organics – Tucson local source of bulk wasp compost (Catalina, AZ)
  • Ametco – source of perforated plastic
  • Rain Barrel Garden – senior couple in Washington with some great photos of their trough garden, also based on the Mary Jane article.