Urban Gardening the SIP Way

For those living in cities or areas where you don’t have access to land for growing your own fruits and vegetables there is still a solution for you. It’s found in the sub-irrigated planter.

Image from GreenRoofGrowers.blogspot.com

Just because you live in a city doesn’t mean you can’t grow your own fresh fruits and vegetables.

What the Heck is a SIP?

The sub-irrigated planter or SIP is a modern form of a raised bed with the added advantage of a self-watering irrigation system. The water is introduced from the bottom of the container, allowing the water to soak upwards to the plant through capillary action.

SIPs can be made from many different containers ranging from large to small. And once you understand the principle of how one is made you can apply that to practically any container and be well on your way to growing a fantastic garden.

Here’s a great video put together by high-school students showing you the principle of 5-gallon bucket SIP and how you can make your own:

Advantages of Sub-Irrigated Planters (SIPs)

Not only is there an 80% decrease in water usage in a plant to plant comparison than found in a typical garden but it also doubles the production output of a garden and on top of that it is weed free! Best of all this system allows city dwellers to essentially bring their own land with them and place it on their balconies, patios or a city roof.

This type of design allows for a bottom up watering approach rather than a top down approach that is typical in potted plants or plants growing in a standard garden. Since the water is pulled up from the bottom, as long as the water reservoir remains full the plants will draw the water as needed. There is no risk of over- or under-watering the plants.

How to Make Your Own

What You’ll Need

  1. 2 five gallon food-grade buckets that can stack inside one another
  2. 1” plastic pipe or tubing (pvc pipe works fine) about 3” longer than the height of one of the buckets
  3. smaller plastic container (a plastic cup or used hummus container works great)
  4. power drill with ¼ inch drill bit
  5. box-cutters
  6. plastic bag large enough to cover the opening of one of your buckets
  7. snips or hacksaw to cut the pvc pipe

Step 1: Prepare the Buckets

Place one bucket inside the other and put them in front of a light source to see the space created between them – this gap will act the reservoir that will hold the water. Measure the height of this space and mark that measurement on your smaller plastic container, starting from the bottom. Add 1/8” to this height and measure the diameter of your container at that height.

Step 2: Drill your Holes

Turn the first bucket upside down and mark the center. Around the center draw a circle whose size to the diameter you just measured on your plastic container. Using this circle as a guide cut a hole in the bottom of the bucket that is just smaller than the diameter of your small plastic container. If you have a jigsaw, use this to cut the hole. If not, drill a series of small holes around the perimeter of the circle and use your snips or scissors to finish the job.

On the same bucket drill roughly 25 ¼” holes evenly spaced around the larger hole you just made.

Step 3: Prepare the Fill Tube

Drill or cut a hole in the bottom of the bucket that corresponds to the diameter of your watering pipe or tubing. Cut the bottom of your tubing at a 45-degree angle to prevent the tube from clogging in your bucket.

Step 4: Cut Slits in your Small Container

With your box cutter slice 4 vertical slits in the sides of the smaller plastic container making the slices evenly spaced around the perimeter of the cup. Do not cut through the bottom or lip of your cup.

Step 5: Stack the Buckets Together and Drill the Overflow Holes

Place the bucket with holes in it inside the other bucket. Place the buckets in front of a light source as you did earlier and drill two ¼” overflow holes on opposite sides of the outside bucket. These holes should be a quarter inch below the bottom of the inside bucket.

Step 6: Add your Potting Mix and Plant your Seedlings

With the buckets stacked together, place the plastic tube through the hole you made for it angled end first. Pack the small plastic container with wet potting mix and set it inside the large hole in the center of the bucket.
Fill the first bucket ¾ full with damp potting mix making it fairly compact. Plant your seedling and top off the bucket with potting mix.

Step 7: Add Fertilizer

Water your seedling from the top, for the first and only time to saturate the soil. After that point, water your plant using the fill pipe. Take one cup of fertilizer and sprinkle it around the outside edge of the bucket leaving as large of a space of plain soil in the middle as possible. Take your plastic bag and make two slits in it, large enough to fit your seedling and watering tube through, respectively. Place the plastic over the top of your bucket while gently feeding your seedling and watering tube through the slits. Secure the plastic with a zip tie or string.

Step 8: Suggestions on Watering

When watering you’ll want to fill the reservoir until the water comes out of the overflow holes. As mentioned before this self-watering system makes it impossible to over-water your plant. Every few days take a look at your reservoir and fill as necessary. During the growing season there may be times when you need to water every day so be sure to pay close attention.

A Word on Soil

It’s important that you do not use standard garden soil in the SIPs. Why? Well in order for SIPs to function correctly the water must be wicked from the bottom to where the roots of the plant can soak up the moisture. Ordinary soil does not provide the capillary action (wicking action) needed to move the moisture upward. You’ll need to purchase potting soil (with the main ingredient being spagham peat and/or coir). Here are some homemade recipes provided by Global Buckets:

Recipe #1: Sphagnum Peat
70% Sphagnum Peat
20% Vermiculite
10% Perlite

Recipe #2: Sphagnum Peat and Coir
35% Sphagnum Peat
35% Coir
20% Vermiculite
10% Perlite

Resources

If you prefer not to make your own, there is a commercial variant of a SIP called an Earthbox which can be purchased at the Earthbox.com site for $50 per box (a homemade one is much cheaper).

Also, here is :

  • Global Buckets: A great site which teaches you how to make an automated watering system as well as fertilizer and soil recipes
  • Green Roof Growers: A blog about three people’s experiences growing heirloom vegetables on the Chicago rooftops using SIPs.

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