Last week, I taught a class on raised beds and briefly showed the participants a mock SIP, sub-irrigated pipe system.
I know I have not posted for a few weeks. Please accept my apologies. I had surgery on that pesky knee that took the brunt of planting the white pomegranate last fall. So, I have been down for the count until this week.
But let’s get back to the SIP.
WATER WITHOUT DRIP
This watering system is very useful for many reasons.
- If you want to place a raised bed on a hard surface, it is often difficult to run a drip system to it.
- You want a raised bed and you don’t have a water line within its usefulness.
- You want to save more water than even a drip system can do.
A SIP may be your answer.
WHAT IS IT?
A SIP is simply 4-inch flexible perforated drainage pipe combined with a thick plastic liner, a short piece of PVC pipe, some landscape cloth and a small tube for drainage. Other than that, you use what you normally do for soil in your raised bed.
BUILD THE SYSTEM
For a 4’x4′ raised bed, you will need two 10 foot lengths of perforated pipe ($7 each = $14), a two-foot piece of 1-inch PVC pipe (if you have to buy a whole pipe, it’s $4 for 10 feet), a cap for the PVC pipe to keep out bugs and soil (50 cents) 2-inch tubing of any kind for drainage hole), 4 x 4 feet of landscape cloth (50 feet is $10), and a small pond liner $15-$20). You can get by with thick black plastic liner.
Your costs per bed for the irrigation system is $31.50, based upon how much is used of everything purchased.
Cut 4 pieces of perforated pipe, 4 feet in length. A box cutter is great for this. About 3 inches into the edge of the pipe, cut a hole big enough for your PVC pipe piece. On the opposite side and opposite corner from the PVC pipe, drill a hole about 1 inch below the top of the PVC pipe (so about 3 inches from the bottom of the raised bed. Cut one edge of your PVC pipe at an angle so that when it rests inside the pipe, it guarantees that the pipe won’t lay flat, preventing water to enter the pipe.
Two schools of thought exist about the landscape cloth. Some people wrap each perforated pipe in landscape cloth, including the ends. If so, you will need about 8-9 feet of your cloth. Others simply wrap the ends of the pipes because they have found that very little soil enters in through the slits. Both work if you use a porous substance like Coconut Coir around the pipes. The main thing is that soil or a wicking product must come in contact with the pipes on top and sides in between each pipe. This is what causes the “wicking,” or water drawn upward toward the plant roots.
Lay the pipes side-by-side with a small gap between each pipe so the wicking product can be worked in between each pipe.
Tuck Coconut Coir in those spaces between the pipes and fill the bed about 2-3 inches on top of the pipes. It is a quality product that holds moisture and wicks the water from the pipes to the soil well. Then I mix compost and potting soil to keep the mix light. If you don’t want to use potting soil, simply mix Coconut Coir, compost and raised bed soil together.
Add any fertilizer or organic amendments that you would like.
Some people cover the bed with plastic to capture the water and cut holes to plant the transplants. I prefer to layer about 4 inches of mulch on top. Either will work.
TIME TO WATER
Fill up the PVC pipe until water flows out of the drainage tube. It means that the pipes are full. Put the PVC cap on the PVC pipe to keep out bugs. Water the soil by hand the first time afterward to help the wicking process begin.
To aid in watering, you can use a funnel on the PVC pipe or make one out of a large plastic bottle by cutting the bottle in half. Remove the cap and turn it upside down. Voila! A free funnel.
NOT A PLACE TO START SEEDS
This style of raised bed really is best with transplants. If you plant seeds, you will still need to water by hand until they germinate and are established.
Check the dampness of your soil either through pushing your finger into the soil to your knuckle or by using a moisture meter. Once you do this a few times, you will know how often you need to refill the pipes.
SIPS, like other wicking techniques, give water to the plants on demand, not on your drip system’s watering schedule.
Give it a try and happy wicking!
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