The water runs deep

I am not a fan of the soil in my backyard.

When I bought my home, I inherited a children’s packed-down race track with only one dying tree in the corner of the yard. The sun had baked the soil for years without benefit of any plants or water to enrich it. The children had sped their trikes through dips and hills, packing the soil down even more than the heavy construction machines that were used to scrape off the topsoil and grade the home when it was built.

As a result, I have caliche (cement-like chunks that can spread many feet wide and up to 6 inches deep) in almost every section of my yard and then above that, hardpan (tightly-packed clay). When I hired a landscaper to install an inexpensive backyard, I agreed unwittingly to pay for landscape rock in areas that didn’t have grass, only adding to my current problem. In the Southwest, we don’t even think twice about doing this, but if you plan to add a garden or more plants later, withhold the rock from those areas. Otherwise, you will find that the rock embeds itself several inches into the soil.

The result: I now have small embedded rocks in the first few inches followed by 12 inches of hardpan clay, supported by a 4-6-inch layer of caliche. Welcome to my garden’s world. If I don’t do anything other than dig a hole, it guarantees a swift death for anything I plant.

The soil probe is 3-feet long. Only about 8 inches went into the ground with very forceful pushing before it refused to go further. A young tree like this should get water down about two feet, which would allow the soil probe to slide into the soil that far down within 24 hours of watering.

A WATER-LOGGED TREE
Last October, I planted a healthy, small ”Wonderful” (its variety name) pomegranate tree. It looked good until a couple of months ago when the fruit and the leaves began to fall off. It was about the same time that I had increased the water frequency for the tree irrigation line because of the summer heat. Water pooled heavily around the new trees while my mature trees were loving it. I tested each tree in the yard with a soil probe to see how deep the water was penetrating. Any tree that had been planted more than a year ago showed a water saturation depth of 2-3 feet, which is perfect. The new trees, however, were only receiving 6-8 inches.

The standing water around the trees made it clear that the soil wasn’t porous enough to accept the water. This caused a dilemma because I couldn’t stop giving the increased water supply to the mature trees but I needed to quit water-logging the young ones. I had already limited the number of open drip lines for the young trees, so I couldn’t cut back on that. There was only one way to go – deeper into the ground to bypass the hardpan and caliche. I decided to use the deep pipe irrigation method. This method has been used in dry lands throughout the world, especially in areas where water penetration is difficult.

The deep pipe (top) is 24 inches long with holes running down its sides. It has a cap on top to keep the water in the pipe and to prevent evaporation. The 28-inch bedding plant auger (bottom) is attached to a corded drill.

DEEP PIPE IRRIGATION
Deep pipes are pounded vertically into the ground around the tree canopy. They have small holes every 2-3 inches and the holes have a thin screen on them to prevent soil from clogging the pipe. The pipes are usually about 2 inches wide and anywhere from 12-36 inches long. Each pipe has a cap on top, both to keep the water from spilling out onto the topsoil and to hold in the drip line, if you choose to use a drip line. They can either be hand-filled, like an olla (last week’s blog), or you can run a drip line into each of them. The pipe fills and pushes the water deeply near the roots of the tree through the holes that run all of the way to the bottom of the pipe.

I purchased three 24-inch pipes to encircle the tree since it is young and the roots weren’t deeper than that. But here’s the problem: if water can’t get through my multiple layers of rock-hard surfaces, how will a plastic pipe get there? I knew the pipe would break apart as I pounded to drive it down. The only thing that broke through in the past was a pick axe, and that wasn’t going to work with an established tree. I went to the Internet and found a bedding plant auger that can be attached to a standard drill. It is 28 inches long and cuts a three-inch-wide hole ($24). You can get them for 2-inch-wide holes also. Either will do the job.

The hole is dug the depth of the pipe, then you slide the pipe down into the hole.

It is best to use a corded drill. In reviews, people said that the cordless drills aren’t powerful enough unless you have a heavy-duty one. Even with the auger, I could only go about 20 inches deep into my soil. I was hitting rocks and roots from an old rosemary bush. You have to go slowly, pushing down a few inches then easing it up near the top, then back down, or it freezes up. Keep checking the tightness of the bit. The pressure will loosen it.

If the drill couldn’t go the full depth, use a rubber mallet to try to get the inserted pipe to go deeper.

Once your hole is dug, insert the pipe then pound it with a rubber mallet until you either reach the height you want or it simply won’t go further. Fill in dirt firmly around the pipe and make sure you don’t have air gaps or these will sink with the water and loosen the pipe from the hole. The water will then rise upward instead of horizontally, which will defeat your purpose. If that happens, simply pack the soil tighter around the pipe. I used several layers of duct tape over each hole that was above ground. If you can get the pipe all the way down, that’s more effective and you won’t have any holes that need to be taped. I then put a drip line into the pipe and put the cap on.

Use duct tape or a similar water-tight product to seal excess holes if any are above ground. If you choose to use drip irrigation with it instead of hand-filling, put it inside the cap opening and place the cap on the pipe.

CHECK FOR SUCCESS
Monitor your tree for a few weeks. You will probably still have surface water because it may push to the surface a bit due to the heavy soil.  If you find that the water still pools and isn’t gone within about 24 hours, or the water is spreading out much further into the yard than your tree needs, you may have to cut the water to one of your pipes temporarily by replacing the emitter in the pipe with a goof plug. A goof plug looks like the regular drip emitter except it doesn’t have a hole in it. You can buy them wherever you get your irrigation supplies. When you need the line again, simply clip off the drip line directly behind the goof plug and place a working emitter on it again.

Once I installed the deep pipes, I put about three inches of good compost around the tree extending to the edge of the tree canopy, then piled some mulch on top of that. Make sure that neither touch the trunk of the tree. Since the mulch retains water, it can cause bacteria to develop on the trunk if it rests against it. The compost will help break up the soil as its nutrients seep down into it.

This should solve my problem and once I do the same for all of my young trees, it should cut my water bill substantially.

You can purchase the pipes at some hardware stores or online. They average in cost from $8-$12 a piece, depending upon size. You can also make your own from bamboo poles or PVC pipe. I have even seen it done using large plastic bottles with holes drilled going down one side and buried into the ground with only its cap above.

Next time I plant a new tree, I am going to make this process much easier and plant the pipes as I plant the new tree. It should give the tree a much healthier start.

Jknapp

I am a certified agriscape designer and Maricopa County Master Gardener. I have been gardening since I was six years old and worked in my grandfather's garden. I believe that the only way to be a responsible gardener is to garden organically. It improves our soil, is safer for us to eat, sustainable and it protects our pollinators and soil from chemical poisoning.