Series: The Organic Gardening Collection
We can’t look at soil management without also looking at water management.
This lesson isn’t a complete summary of strategies, but it does cover some of the most important points we need to know.
Seedlings in the rain
While perhaps not as exciting as say, the latest fertilizer or microbial inoculant, water is more important.
Proper water management comes before these other topics and is one of the most important things we do.
Water is essential to life.
Not only do we drink it — we are made of it. Throughout the course of our life, our bodies contain between 50 and 80% water. We know our plants are made of water, too, and they need it for photosynthesis and cooling.
What is often overlooked is that all living species in our garden need water. Sure, it’s a great idea to provide a water source for birds and other animals, but I’m referring here to the soil life.
Insects, earthworms and microbes all need water. It’s vital for the health of the garden that they have enough water. Remember, they make good soil and feed and protect plants. And interestingly, a biologically active, nutritionally balanced garden will also attract more water in the form of dew.
Not enough water in the garden is devastating and very common. Too much water is also common; more specifically, frequent, shallow watering.
Irrigating daily for 20 minutes often encourages roots to stay comfortably along the surface of the soil instead of searching further and deeper, which is important for a sustainable, healthy garden.
If you irrigate with water that is cleaned by the city, it probably isn’t overly high in any of the trace elements, nitrates, salts or microbes such as E. coli, so you shouldn’t need to test for that.
It doesn’t mean that it’s high-quality water — in fact, most of it isn’t. Chlorine, fluoride and other toxins are generally used to clean it up before it gets to you.
That’s why capturing rainwater is so important. Ideally, we would capture all the rainwater that falls on our roof and run it through a pond or series of ponds that clean it up using specific aquatic plants and microbes.
Wells and open ponds should be tested. They are all contaminated with pesticides now to some extent, but some more than others.
Test any water that could end up in your garden, even if it looks clean and natural.
You can test for some things yourself with special test strips, such as nitrates and salinity, but I tend to get a lab to do that along with all the other important things.
Our Water Supply
Aquifers around the world are drying up, including in the U.S. and Canada.
The gigantic Ogallala aquifer in the Great Plains, which gives the U.S. about 30% of its irrigation water, is being used at many times the rate it’s being recharged and may be dry in as little as 25 years.
Half of the wetlands around the world have been lost since 1990. At least a third of rivers and streams in the U.S. are so polluted that fish contain toxins and are inedible, and swimming isn’t safe. Lakes are worse off.
Farming accounts for about half of this pollution. The majority of wells have pesticides and even more of them have pharmaceuticals and other man-made toxins. Even in rural areas, many of our wells are contaminated with pesticides and excess nutrients.
In the city, substances like fluorine, chlorine and chloramines are put in our water in an attempt to clean and improve it.
Some of it is necessary and definitely helps make our water safe to drink, but some of it is unnecessary and harmful to us. None of it focuses on the root cause of the problem, which is the absurd chemicals we shouldn’t be producing and disposing of in the first place.
The implications for you and me are that we need to stop using toxins in all areas of our lives and start protecting our water supply, find ways to collect and recycle water, and then responsibly use municipal or well water to make up for what we can’t collect.
You might also consider doing something to clean your drinking and irrigation water, some combination of ozone, ultraviolet light, carbon filtration, reverse osmosis, hydrogen peroxide, ion exchange or distillation. I have a relatively inexpensive filter for my drinking water that takes out 99% of the chlorine, lead, pesticides, cysts and many other compounds.
To protect our water, we can start by not using pesticides, chemical fertilizers and genetically modified products.
We can also establish a garden that is teeming with plant and microbial life in order to clean up toxins and pollutants. There are certain microbes that specialize in doing just that, such as the Rhodopseudomonas palustris found in many microorganism inoculants.
Before we look at irrigation, let’s first look at how we can save water.
The first method is rain harvesting. While a rainwater barrel is a good starting point for water conservation, I find it interesting to actually run the math and see how little water they hold. I wonder if they are taking the limelight away from more important methods.
Rain barrels look eco-friendly, but how much water does one actually hold?
Heide Hermary of Gaia College showed me this. If your roof is 1,000 square feet (93 square meters) and you get one inch of rain on a spring afternoon, you’ll have 625 gallons of water coming off that roof.
Where I live, one inch of rain is fairly common during a storm.
Let’s say you’re collecting that rain into only a 60 gallon rainwater barrel. It will get nice and full and you can use it to water your tomatoes another day, but 90% of that rainwater is going elsewhere.
Your barrel can only take 1/10 inch of rain from that 1,000 square foot roof, so while I like the 60 gallon rainwater barrel, I think there are better solutions, especially if you have long dry spells during the summer.
A 600 gallon rainwater cistern could handle almost a full inch and a 1,500 gallon cistern could easily take two inches of rain. Think of it as a giant rainwater barrel.
Ideally, almost every house would have one of these, the size dependent on the amount and seasonal patterns of rainfall in your area. If you don’t like the sight of them, they can be cleverly hidden or even buried.
The thing is, they can also be expensive. A more attractive and potentially less expensive solution would be to build a small pond, bog or rain garden into which you can direct the roof water. A pond the size of a king-sized bed and four feet deep should hold an inch of rainwater off the roof.
A pond this size can make a decent reservoir, and has other benefits like cooling your garden and providing habitat for beneficial insects.
If constructed thoughtfully, it can also provide drinking water for insects and animals. Most gardens should have some open water for this purpose, with places for insects to stand while drinking so they don’t drown.
Mosquitoes aren’t a problem if you keep the water moving and use larvae control methods.
Rain Harvesting Into the Soil
While cisterns and ponds are a better option than a rainwater barrel, we should mostly be focusing on the ultimate storage solution, the soil.
The soil is the best way to hold onto water and makes rain harvesting using a rainwater barrel look like child’s play.
A loamy sand without organic matter, which is 70-85% sand, and not very good at holding water, can hold at least two inches of water.
Of course, just how much depends on how wet it is already, the health of the soil food web, compaction and so on. This loamy sand could potentially store that inch of rain plus the extra inch from our roof if we could somehow direct that inch evenly over 1,000 square feet, which we probably can’t, and if the infiltration rate of the soil is high enough, which it may or may not be.
Soils higher in silt and clay can hold four to five inches of water, but infiltration rates on these soils are generally much lower than a downpour of one inch of rain per hour, so they may have enough to handle with the rain alone unless it comes gradually over a few days.
So what to do?
There’s one thing we can put in and on our soil that will hold the extra water, and that is organic matter.
Organic matter is a rain harvesting bonanza. Various research has tried to determine how much water organic matter can hold, often concluding it can hold tens or even hundreds of times more water and nutrients than the same amount of soil.
Even if it holds only four times its weight in water, you can hold nearly an extra inch of water if you can increase the organic matter content of your soil by just 1.5%, and this is easily doable.
Soil with high organic matter content is less prone to flooding and runoff.
A study in the Journal of Soil and Water Conservation found that regardless of the type of soil, “as organic matter increased from 1-3%, the available water capacity approximately doubled.”
That means we can now be harvesting two or three inches of rain from the roof, 20-30 times more than a 60 gallon rainwater barrel can hold.
Organic matter can be brought in as compost and mulch. Even incorporating two inches of good compost into the top 12 inches of a new garden bed will often increase the organic matter content by 2-3%.
It won’t increase the stable humus that much, but I’m just talking about any organic matter here. Mulch goes on top of the soil, but it holds a lot of water, as well.
Your soil should always be covered in mulch, and when possible, plants. This improves water infiltration and decreases evaporation. Now all that’s left is to direct the runoff to your gardens with gutters, and perhaps slight grading of the ground, using techniques such as swales and berms.
Another of our goals is to keep continual plant cover in the garden.
This vastly improves the ability of the soil to hold onto water. It slows down rainwater, giving the soil more time to absorb it.
Plant root systems open up channels in the soil that allow water to infiltrate more easily and deeply. The plant canopy decreases evaporation.
Plants are often blamed for using too much water. Interestingly, in places where large amounts of forest are being cut down, the rivers are drying up and the precipitation in the region is often decreasing drastically.
We actually need these plants and microorganisms all to be happy and healthy in order to have a healthy water supply. A multilevel planting made up of groundcovers, flowers, shrubs and trees may use more water, but it will also improve soil conditions so the soil can hold more water.
Drip irrigation was developed to save water by dripping it directly to the roots of plants rather than spraying the entire landscape.
Note that I’m not talking about soaker hoses or micro sprays. Drip irrigation is where tubing brings water to tiny nozzles that drip water directly into pots or right onto the soil beside each plant in the garden.
There are new systems that can distribute the water further, but the classical approach is delivery just to the plants.
Note how dry the surrounding soil is.
Drip irrigation was designed for farming in very dry climates where water is scarce. If calibrated correctly and properly managed, it can work to save water in an agricultural monoculture situation.
In fact, some people think it was one of the most important technological developments for agriculture. It’s useful for the above purpose, but it has made its way into residential gardens where most of the time it’s inappropriate because it waters a tiny area right around the plant, ignoring the rest of the soil.
This is problematic for two reasons.
Roots look for moisture and stay away from areas that are dry. With the frequent, shallow watering of drip irrigation, the majority of the roots will tend to stay right by the plant instead of reaching further into the soil for water and nutrients.
This means most plants will never reach a state of optimal health. Instead, there’s a good chance they will be unstable and unhealthy, covered in insects and disease and on their way to an early death.
Many times I have put a shovel into the soil 18 inches away from a drip emitter and found it to be totally dry.
The rest of the soil needs water just as much as the plant because the microorganisms, earthworms and insects need water, not only for their own health, but also in order to give the plants nutrients, water, a healthy organic soil environment, and protection from plant-feeding organisms.
Remember, plants get all of these services from the organisms in the soil.
Drip irrigation may save water in the garden, but at the expense of the plants we’re trying to grow. Also once grown these plants would actually attract water into the landscape, sequester carbon, produce oxygen, feed bees, butterflies and other animals, and cool our houses and cities.
That being said, enough people are successfully using drip irrigation to grow food for me to mention that it’s not only possible but may become very important as our fresh water sources continue to dwindle.
These folks should be commended for finding these kinds of solutions that may become necessary. One alternative method is to make the top three to six inches of soil dry and not use mulch, thereby decreasing evaporation from the soil surface and saving a lot of water.
A subsoil agricultural irrigation system in Italy.
This method generally requires chemical salt fertilizer use, so as I see it, there’s a good chance of producing food that is substantially less nutritious in the long run.
My viewpoint is that if we’re ultimately decreasing the organic content of the soil, killing the soil food web, and supplementing with imbalanced nutrition, our food will reflect this.
Providing the Right Amount of Water
Of course, we definitely want to save water. It’s absurd how much water goes into our gardens — especially our lawns. That’s why I think about collecting and storing rainwater before I think about irrigation.
Most of us will need to irrigate, especially when we’re establishing new gardens or growing food. We can use captured rainwater for a lot of this.
I recommend irrigating with anything that provides water to the entire landscape: by hand, with a sprinkler, micro spray heads, or even soaker hoses if they overlap enough, although the latter really only have occasional usefulness.
Hand watering is time consuming, but allows you to have a closer relationship with your plants.
I wouldn’t worry too much about evaporation with overhead watering, as research from the University of Nebraska shows this to be a less than 4% loss.
Some gardeners don’t like to apply water to the leaves because the conventional wisdom is that it promotes some disease, and that’s true in some cases, especially when watering at night
I like to apply water from a sprinkler that gets the leaves wet because that’s how it happens in nature when it rains. I do this in the morning.
If I’m using chlorinated city water, however, I may apply it more to the soil to avoid killing microbes on the leaves. Of course, the microbes on the soil surface won’t be too happy, but we work with what we have, right?
It’s difficult to determine exactly how much water to apply.
People have developed mathematical equations and charts and calculators to help with this, and while these tools are helpful, it’s hard to find accurate parameters that you need to feed into these calculations.
For example, how deep do your plant roots go? This is especially difficult to figure out when we’re growing many different kinds of plants. How much water does your sprinkler apply per minute? What is the evapotranspiration of your area?
You can find these things out and it’s important to do so in a landscape where you’re designing an automated irrigation system that has to work without you being there, but for home and market gardeners who can pay more attention to our gardens, I prefer to go by feel.
You want to water deeply to encourage the roots to go down, and then allow some time for the soil to partially dry out, but not entirely. It should be thoroughly wet after you water it, but not to the point of runoff. Even though you should water more deeply and less often, your mulch layer should generally stay good and moist.
Make sure you check under the mulch layer, to make sure the water has penetrated deep into the soil.
A slope may need to be watered in stages, such as 10 minutes on and 10 minutes off for an hour, in order to allow time for the water to infiltrate rather than run off. Sandy soils can’t hold as much water, so they need to be watered more often throughout the week with less water.
Silt and clay soils are watered less often with more water, although if they have low infiltration, they may need to be watered in stages like a sloped garden.
As your soil organic matter and biology improves, you will be able to water substantially less. In fact, you’ll have to, or you may drown the life in the soil. The soil will hold water just so much better as it comes alive.
- All organisms in the garden need water, which is why drip irrigation is often inappropriate for our purposes.
- Everyone should collect rainwater in cisterns and ponds. Best of all, though, is to have a soil with a lot of organic matter and vegetation, including multi-level plantings where possible.
- Water with anything that deeply wets the entire soil, adjusting it based on the soil texture, infiltration rate and organic matter content, and keep that mulch layer moist.