How to make Sub-Irrigation Planters (SIPs)

Sub-Irrigation Planters (SIPs) are portable, self-watering containers that can be built in any number of sizes to accommodate different vegetable types and sizes. 

  

 

 

 

 

The basic Sub-Irrigation Planter has three layers - the bottom layer is water, the middle layer is air and the top layer is soil.  The top layer has two pockets that extend down into the water, wicking the water up into the soil as needed.  Because plants need oxygen to their roots, you don't want the soil to sit directly in the water.  The planter has a floor that sits above the water line, providing an air layer between the soil and the water that provides the needed oxygenation to the roots and prevents the plants from drowning.

You only need two water wicking pockets to keep the plants watered appropriately.

 

Sub-Irrigation Planters (SIPs) are pretty easy to do yourself.  To make your own, you will need the following items:

1 - 30 gallon plastic storage tote (we use sterilite because they are more rigid) $11 each

1 - 10 foot length of 4" flexible perforated pipe (can make 2 ½ boxes with 1 pipe)  $6

1 - 1" plastic tube (thin wall)  $2

Landscape cloth

Scissors

X-acto Knife

Drill with 2 drill bits.  7/32” and ½”

Small saw for cutting plastic tube

Brown plastic paint (Krylon)  $4

1 cubic feet potting soil  (big bag) $7 - $12

Start with a 30 gallon storage tote. We like to use the Sterilite totes because they are more rigid. Rubbermade totes are flexible and will not hold their shape well.

Remove the lid and set it aside for now.

 

Measure the length of the tote across the top and inside the bottom. Our 30 gallon storage totes are about 29”tall across the top. They are also about25” long in the bottom of them.

Using the measurements across the inside bottom, take a pair of scissors and cut your flexible perforated pipe into sections.  You will need to cut the following 3 pieces:

2 – 25” pieces  (bottom inside length)

1 – 15” piece (bottom inside length minus 10”)

 
 

Perforated pipe has holes in it that allows the water to flow in and around the pipes.  This provides support for the floor while allowing the water to flow to all areas in the water reservoir.

 

After the 3 pieces are cut, lay them in the bottom of the storage tote.  It’s ok if they are a little tight.

 

The short piece should be on one side and placed so there are 5” gaps on each end of the pipe.  This is where the water wicks will be located. 

 

Next we work on the floor that lays on top of the perf pipe.

 

 

 

Set the lid on a hard surface that you can cut on.  I usually use the ground or our old picnic table.  You are going to cut all the way through, so you will scratch the surface below the lid.

 

 

If your lid has an indentation in it like ours do, use that as a guideline for cutting.  If not, then make a line 3" in from the edge and cut the lid center out using a sharp X-acto knife.

 

 

 

I have found that it works best to do this type of cut in two passes - one pass to score the lid and the second pass to actually cut through the lid. 

 

 

 

 

 

 

Cut all the way around the lid so the center comes out. 

 

Set the outer piece aside.  It will be painted and put back on the box top later.

  

Keep the center piece. We will continue to work on this piece to make the floor of the SIP.   

 

 

With a sharpie marker, draw two  4" x 4" square corners on one long side of the floor piece. 

This is only done on one side of the floor.  When you are done, there should be two squares drawn on the floor piece.

 

 

 

 

Using an X-acto knife, cut out the two corner pieces from the floor piece. 

 

This will be the pockets in the floor that create the water wick pockets.

 

 

 

 

 

 

 

Try out the floor in the planter.  The base should sit directly over the perf pipe and you should be able to see directly to the bottom of the planter where the water wick pockets are located.

Next we drill vent holes in the floor with a ½” drill bit.

 

 

I place the floor piece on the ground and stand on it for support, then I drill holes about 4” apart all over the base. Its ok if this is not perfect, you are creating airflow holes. 

 

 

 
 

 

 

 

Next we cut the 1” stand pipe that lets us water the planter from above.  The pipe should stick up about 3” from the top of the planter.  We cut ours about 18” long.

 

After you’ve cut the pipe, drill water holes in the end of the pipe using the 7/32” drill bit.  This helps the water flow into the reservoir when you are topping it off.

Place the stand pipe in the OPPOSITE side of the box that the pockets are on.  If the floor is too tight, cut a notch in the floor to accommodate the stand pipe.

(this photo is from our tree planters, which are larger)

 

 

 

 

At this point we add 5 holes for water overflow and air flow.  The holes and the stand pipe go on the opposite side of the planter from the wicking pockets.  

 

 

 

 

 

 

 

 

 

Using your sharpie marker and the diagram below, mark the 5 holes, 3 on the bottom and 2 on the top. 

The 3 water overflow holes should be placed 3” from the bottom of the planter. 

The 2 air holes should be 4” from the bottom of the planter.

Use your 7/32” drill bit to drill these holes.  They don’t need to be very big to be effective.

 

 

 

 At this point I stop and spray paint the outside of the box, the lid, the stand pipe and the inner top of the box with a spray paint made for plastic.  Krylon makes a great dark brown one that looks like dirt and makes your planters blend in.

 

 

Next we cut our ground cloth and add it into the planter.  We use the kind that is about 32” wide and allows water to pass through it, so the  water wicking pockets will work properly.

  

Measure out about 6’ long, and lay it in the bottom of the planter, wrapping it loosely up the sides.

 

 

Now press your hands into the wicking holes, making pockets with the ground cloth.  Make sure the ground cloth wraps up the sides of the wicking pockets, so the dirt does not escape into the bottom and become mud.

 

This will keep the soil separated from the water, but creates the water wick pockets that can absorb water through the holes in the ground fabric.  

The last step is to add soil to the box and get it ready for planting.  I use a potting soil in the box, but your own soil/compost mix will also work well. 

 

ADDING SOIL 

You can fill this 30 gallon SIP box with a 2 cubic foot bag of potting soil.

 

 

Slowly fill the box ¼ full and press the soil down into the water wicking pockets.  Continue filling the box to half full of soil and then stop and lightly water the soil to activate the wicking. Put the rest of the soil in the box and water the soil again. 

 

A water filled SIP box is heavy - about 50 pounds or more.  Its alot easier to set the box in the location you’d like it in and then water the soil well to saturate it.  Focus on spraying water over the wicking pockets, so the soild is wet from above as well as from below.  After the box is well watered, use the stand pipe to fill the box until water flows out of the lower set of holes.

 

PREP FOR PLANTING

I like to add a few things to the soil before I add my plants or seeds. 

1.  Add in a cup or two of dolamite lime.  This is a powdered lime with magnesium in it.  Your plants will love it.  Mix it into the top 4 inches of the soil.

2.  I also mix a 10-10-10 fertilizer in the top 1" layer of soil and plant with desired vegetables. 

 

After that I plant my seeds in the box the same as I plant them in the ground or put in plants if I've started them early or bought them pre-started.

 

**I've been trying out a few products from Hendrikus Organics this year and they seem to be doing well with the plants.  In addition to the things I do above, I also add a small handful of Humagic and Organibloom in the planting hole and place the new plant on top of it.  I'll keep you posted on how well they do over the summer, but so far things are going well.

 

From this point the process is pretty simple.  Water the boxes every day and wait for things to grow in and start producing food for you.

 

I keep track of how long it takes to 'top off' a box by counting while I'm filling.  You can use this method to track how quickly your plants are taking up water as they hit their growth spurts or deal with the summer heat.

 

Next I'll post more information on how many of each plant you can put in this sized Sub-Irrigation Planter.

High Production Container Gardening in a Small Space Using Sub-Irrigation Planters (SIPs)

We live in an older house on a larger city lot, with a shady back yard and a small sunny front yard, so we struggle with limited space for a vegetable garden, like many people do. To work around these factors, we use a sub irrigation method of gardening that allows us to do high production container gardening on our asphalt driveway. 

We have found this approach to be very flexible and accommodates our lifestyle and gardening goals.



Sub-Irrigation Planter Box

Using a Do-It-Yourself sub-irrigation approach, we make our own closed system planters. These are large plastic storage totes that we modify to add a raised floor with a 5 gallon water reservoir in the bottom and an overflow vent.

The plants water themselves as needed though water wicking. This approach makes it easy to water your garden, use water efficiently and not have to worry about under or overwatering.

I'll make a page that shows how to make these planters in a future post.




Vegetable boxes kept under cover in a warm place


Once the planters are up and going, they are very low maintenance and completely portable, so they can be moved in and out of a greenhouse for extended growing. 


This is also a great way to start a garden in a limited space or in cases when you are unsure about where the final garden location will be. 





We start our boxes in a greenhouse as early as February.  The boxes are kept in a group in a warm area until late spring.
 

This set of boxes contain lettuce and peas. We started them early and set them out under a plastic cover to create cold frames. This helps get a jump on the growing season.

SIPs in the driveway

We move the boxes out into the driveway once it is warmer. In this case, we started out by tucking our SIP boxes against the retaining wall at the side of our driveway, where it is very warm and sunny.




Tomatoes grown over a arbor gate

We grow all kinds of vegetables in these systems, including corn - which gets quite big and loves to suck up water.




Tomatoes also get big and consume alot of water, so we grow two plants in each box to control the crowding problem that occurs over the summer.  Very large tomatoes are trained to an arbor gate to support the weight of the plants, improve airflow and make it easy to harvest as they ripen. 







We bring in a steady flow of tomatoes (and everything else) from late summer until frost, when we clear the vines and have alot of green tomatoes.








Watermelon Trellis

Cucumbers, watermelon and peas are grown vertically on trellises.  We like to grow Tiger Baby watermelons because they stay small and we can suspend/support them in little slings from the trellis.


 

Assorted Peppers

We reuse the soil each year, but practice 'crop rotation' in a way that rejuvenates soil (last year corn, this year beans, etc).  Except for the asparagus, it stays put permanently. 



We augment the soil each spring with compost, lime with magnesium and a fertilizer.  We typically grow all the normal vegetables that you'd expect in a garden.






Apple Tree in a pot


We also use this approach for our fruit trees, though we actually use a combination of three techniques - bonsai, espalier and sub irrigation.

The fruit trees are started in 24" pots and grown for 2 - 3 years until they are ready to go into the larger sub irrigation planters (it is easier to move the trees around and find where they do best in the smaller planters). These fruit trees are semi-dwarf and root trimmed every third year.

Tree with Espalier

After they have grown branches that are long enough to train - generally on their third year - we build a bamboo "table espalier" about 5' above the tree and train the branches to the trellis.


The overhead trellis achieves many things at the same time - it supports the weight of the fruit and protects the branches from breakage, it provides good air circulation which reduces disease and fungus, it makes the fruit easy to harvest and the tree is easy to prune and check for bugs or other health issues.



We grow quince, apples, pears, cherry, peach, and nectarine this way.  We also grow hazelnuts in containers using the bonsai method.





There is a specific approach to fertilizer when growing fruit trees in a container/bonsai approach.  You use a different NPK ratio than normal and you add it a lot more frequently.  I'll go into that in more detail in a future post.





Heronswood Visit

May 18th was a wonderful day.  Heronswood was open to the public for the first time in over 6 years.  

Heronswood is one of those wonderful places that have specialty gardens featuring rare plants and a shade garden that crawls around the woodland floor and shows you what you can do with shade, when given a chance and an adventurous heart.

The Grotto at Heronswood

 

I was delighted and we made the hour and a half drive up to Bainbridge Island extra early that Saturday.  Not only was the garden open, but there was a big plant sale with all my favorite rare plant dealers attending, which meant there was a good chance I could pick up a couple of the items I need to round out the shade garden here.

First thing when we got there - Shopping!!  It didn't take long before I rounded up a beautiful Podophyllum delavayii and a hexandrum for my growing "podo" collection, as well as a couple different Diphylleia grayi and an extra bronze Rodgersia.  After quite a bit of back and forth, I took the plunge and bought an arisaema tortuosum - a 'jack in the pulpit' that could easily get 5' tall, which is why I've held off for so long.  (I have several jacks of assorted type, so it really wasn't that much of a stretch for me).

Paris thibetica

 

I kept eyeing (and finally caved in and bought) a beautiful Paris thibetica from Windcliff/Dan Hinkley.  If you've ever been 'on the fence' about buying a rare new plant, I can tell you that asking one of the country's most highly respected plant collectors his opinion on it is a sure way to guarantee you buy the plant - which is exactly what I did.  

 

 

Columns in the forest

 

After we finished our shopping, we put the plants in the car and headed into the woodlands of Heronswood.  I knew I was in the right place when we quickly came across a mythical looking collection of columns standing quietly among the darmara peltata, rogersia and podophyllums.  It was so unexpected and yet so natural there.

Back Yard

After a long stroll through the woodlands we arrived at the original house and the gardens surrounding it.  Each area was done in different garden styles and was amazing, even as it is in the process of being restored by the Port Gamble S'Klallum tribe and Dan Hinkley.

 

 

 

 

 

Formal Garden

 

 

 

The Formal Garden was just starting to sprout and the bright green boxwood pattern stood out strongly against the surrounding trees.  It would be great to come back here later in summer and see how it has changed.

 

 

 

 

 

 

One of the coolest garden was this huge roman arches made from carefully clipped trees that had been planted very closely together.  When you get up close to this room, you can see that the entire structure is strictly trees, no fencing or physical structure has been added to this.  Inside the garden there is a smaller knot garden.

Roman Arches

 

Driveway / Entryway

 

 After leaving the room of arches, you walk out the back and to the driveway that approaches the back of the house.  This large bed served as a strong focal point before your eye is drawn to the green arches of the room behind it.

 

 

 

 

Driveway Border

 

 

On the way back up the drive there is a long rectangular garden and a row of hedges creating a clear separation between the wild forest and the structure of the formal gardens.






 Peony Tree

On the other side of the road is a very large peony tree that had just finished blooming.  I'm not sure which made me more jealous - the huge peony tree or the large batch of darmara peltata growing next to it. 


From this point we wandered back into the woodlands and up to the Grotto before making our way through the wonderous forest to the old nursery space and plant sale.




If you've never been to Heronswood before, you owe it to yourself to go if the opportunity presents itself.