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Don’t Panic, It’s Organic: Is subsurface irrigation good or bad?

Andy Lopez, Contributing Columnist/Invisible Gardener
7:34 am PDT August 10, 2017

I recently received an email from a reader who says that subsurface irrigation is bad and also way too expensive. She says that it was more natural to water above the soil and not below it.

I started thinking about it.

First off, yes, it is expensive, and up until recently, they did not work well underground. The drip heads were never meant to be buried and would get clogged within a year. Further, animals and insects love the water source and often destroy the drip head and eventually clog it.

There are recent developments in driplines that are built especially for being buried and watering underground (subsurface irrigation). One company in the field is Rain Bird, which has a new line of subsurface irrigation called XFS Subsurface Dripline. It is way too expensive for the average homeowner, but if you have a large property and want to be able to better deal with climate changes, you should look into this system. For the average homeowner, I would use this system in my raised beds and around my fruit trees and trees. 

Because the water is below ground, you can water longer while retaining most of the water, allowing for deep watering. Trees would love once every two weeks or even once a month depending on the soil and the current climate conditions. Here in Southern California, trees will do well with once-a-month deep watering, provided your soil is properly composted and mulched over. Otherwise, evaporation will remove the water as fast as you put it down due to the heat. Protecting the soil from the heat will go a long way in keeping the water in the ground.

If you follow my column, you know I am constantly saying to keep the water below ground and only water a small amount on top. Top watering is necessary for all plants because they all have surface roots as well as deep roots.

Just watering below ground is not entirely right since plants need their surface root system, but watering only on the surface is not all good either since that damages the deep root systems — especially when it comes to trees. If you live in an environment that is natural and has not only good top soil but a deep underground watering system, then you never really have to water the trees. They will get plenty from below and from whenever it rains.

Let’s talk a little bit about rain. When it rains, the water gets absorbed by the topsoil and refreshes all the top surface roots. This water will eventually find its way into the surface water. What is natural is topsoil being watered by rain, which also refills the deep water sources.

When I lived in Florida, it would rain every day during certain times of the year. All that water would get absorbed and flow to other underground sources or go back into the ocean or lake. 

But then it would go through a dry spell. During this time, all the plants and trees would absorb the nutrients the water brings as well, slowly allowing the soil to dry. 

Here in Southern California, and especially here in Malibu, we have no topsoil. The top layer of soil is different here than in the forest. With what small forest we do have, the topsoil is very shallow. 

This has not always been the case. We have made significant changes to the way things naturally occur and have stopped the natural process of recycling that Mother Nature has set up. Many places that I have looked at around Malibu literally have no top soil, only what is left of the subsoil, which is made up of rocks. Rock is what you get when you add water to clay and then add heat, As the soil heats up because of climate change, and we try to compensate by watering more, the clay absorbs the water and when the heat comes, it starts to harden and eventually you will get rock. This rock can become a layer called hardpan, which will not allow air or water through. 

Many folks in Malibu and the surrounding area have hardpan on their property and do not know it. Hardpan slowly kills your trees, and no amount of fertilization or watering will help. Remember how you were watering 10 or 15 minutes every day? That set you up to get hardpan in your soil. 

There are ways to remove the hardpan, but it can take years to remove it completely. There are short-term solutions and long-term solutions. Short-term recommendations include installation of a 4-inch PVC line about 6-feet long into the area about 20 feet apart. Each should have a four-gallon-per-hour drip head and be on its own program so it is only watering that area. 

Watering alone will not solve this problem. You will also need a fertigation unit and to inject microbial life into the clay. 

Next week, I will cover the steps to hardpan removal.

Any questions? Email me at andylopez@invisiblegardener.com. Did you get my new book, “Don’t Panic, It’s Organic!” yet? The eBook version is free just by mentioning Surfside News!