Tag: drought

Don’t get hosed: exploring the efficiencies of garden and landscape irrigation systems

As many parts of the US face drought or dryer than normal conditions and issues about water availability especially in the western states, many gardeners are reassessing their relationships with plants and irrigation.  Many gardeners, especially in the west, are replacing their lawns and landscape plants with more drought and dry-weather tolerant options.  But there still are times when irrigation might still be necessary, e.g., growing vegetables and fruits, establishing new plants, and more.  Using water efficiently and effectively is key in these situations even when water is available and drought conditions aren’t as prevalent. Efficient water use and good irrigation can also mean a savings on the water bill AND a reduction in plant diseases spread by water application on the leaves. Paired with mulching, efficient irrigation can drastically reduce the amount of water used in gardens and landscapes.

 In order to make the best choices for your garden, I’m going to talk through some of the most and least efficient irrigation methods for your gardens and landscapes. I’ll be starting with the most efficient methods and working my way to the least. 

Drip Irrigation

Drip irrigation is considered one of the most efficient methods of irrigation because it applies water directly to the soil at the base of the plant and therefore typically uses the smallest volume of water. Research shows that drip irrigations have around a 90% efficiency rate. . Most systems sit above the ground and apply water to the soil surface, but some sub-soil systems are available. The system usually involves a filter and pressure regulator to keep the emitters functioning and applying water at the proper volume.

This drip tubing has pre-installed emitters along the tube and drips small volumes of water directly on the soil near the plant.

The efficiency of drip irrigation comes with a caveat though. When applied to sandy or rocky soils, water from drip irrigation has a much smaller spread laterally in the soil due to less capillary action and higher gravitational pull due to the large pore spaces. This means that there isn’t as much coverage of water in the root zone. In order to combat this drip emitters must be closer together or have a high flow rate, both of which increase water usage and reduce the effectiveness of drip irrigation in sandy soils. Read more here

Source: Soil Type Influences Irrigation Strategy, MSU Extension, Ron Goldy

There are typically two types of application methods: tubes or tape that have pre-made emitter holes at set distances that disperse a set amount of water per hour or emitters that are inserted into the end of solid tubes (that may or may not have an adjustable flow rate).  The tubes and tapes that have holes pre-made are typically used in vegetable gardens, row crops, or in beds where plants are uniformly planted.  Systems with the inserted emitters are often used in landscape settings where it makes sense to water individual plants, such as trees, shrubs, or large perennials. 

Given the low volume of water disbursed by the system, water pressure is regulated in a way that ensures even distribution as long as it isn’t modified than from the manufacturer or factory specs.

For information on installation and maintenance, check out these resources:

Drip Irrigation for Home Gardens – Colorado State Univ. Extension

Irrigation Video Series – Oklahoma State Extension

Microsprinklers

Microsprinklers function on the same type of system as drip irrigation and can sometimes even be combined with drip systems.  Instead of small openings that drip water on a small area on the soil, microsprinklers spray a small volume of water over a set radius.  The sprinkler heads are typically only a few inches above the soil and therefore apply the water at the base of the plants. Some systems allow you to switch out sprinkler heads that spray in different patterns and distances.  One such system that I’ve used has sprinkler heads for patterns from 90 to 360 degrees and from one foot to ten feet in diameter. 

This microsprinkler has an adjustable head to apply water in a 1 to 5 foot diameter.

While not as efficient as drip, microsprinklers are more efficient than other systems due to low water volume and consistent pressure throughout the system.  They can be more flexible than drip irrigation in settings like landscape beds and around trees and shrubs since one emitter can water a larger area with less tubing and fewer parts. 

Soaker hoses

Soaker hoses are popular because they are plug-and-play.  You can just attach them to your faucet and don’t have to worry about cutting and assembling tubing and parts. Water is released through the surface of the entire hose, making water application much less precise that drip and microsprinklers as well. Keep in mind that soaker hoses don’t have pressure regulation like drip and microsprinkler systems do so you’ll often find inconsistent watering when you use them.  More water leaves the soaker hose at the end closest to the faucet and less (or none) at the far end.  The result is usually excess water in some parts of the garden and not enough in others. 

Soaker hoses also release a much higher volume of water than drip and microsprinkler systems, which can result in overwatering and water waste. I learned this from experience when I accidentally left a soaker hose running for about three days.  The garden was nicely flooded and the water and sewer bill topped out at over $500 that month. 

Sprinklers

Sprinklers are probably the most common irrigation system used because of their simplicity.  Home gardeners might use the hose-end individual sprinklers purchased at the garden shop which can quickly water a large area.  And many homeowners, especially in areas where there isn’t rainfall sufficient to support grass growth, have sprinkler systems installed in their lawns.  However, sprinkler systems are only around 65-75% efficient. Spraying water in to the air, especially on hot and dry days, reduces efficiency through evaporative loss.  Sprinklers are also less precise in where you can aim and apply water. There’s also the added issue that overhead application of water can lead to or worsen plant disease issues by making conditions favorable for the spread and growth of fungi and bacteria. If possible, use sprinklers only on a temporary basis like establishing new plants or make sure they are calibrated effectively.

Hand watering

While hand watering probably uses a smaller volume of water than sprinklers and you can direct water more precisely, there are still issues with evaporation and overhead watering.  In addition, hand watering is usually less effective than other methods because humans are impatient and actually don’t water long enough.  Most plants will benefit from a long, deep watering but many gardeners will only give a pass or two with a water hose and will underwater plants.  This can cause roots to accumulate in the upper layer of the soil and increase long-term water needs of the plant.  Rely on hand watering for temporary needs like plant establishment or container plants (though you can use drip and microsprinklers in containers as well) and use a more efficient strategy long term. 

I recently worked with a local community garden to install several thousand square feet of drip irrigation. The system will save them many hours of hand watering labor each week.

Wrapping it up

There are a number of ways you can manage the water needs of your landscape, from renovating your landscape with more water efficient plants to making more efficient use of water through effective and efficient irrigation systems. As more and more cities and states across the US place restrictions on water use having several irrigation tools in your toolbox will be helpful.  Always remember that the best strategy is to grow plants suited to your environment to reduce water use in the garden. And in places where there isn’t sufficient water for grass to consider removing lawn and replacing with native vegetation and xeriscaping.  Irrigation systems can help in areas with unexpected drought or weather issues but for long-term sustainability gardeners in drier climates should adapt their properties where they live.

Other Sources

Drip Irrigation

Plant lists that shouldn’t exist

Nothing drives me crazier than simplistic solutions to complex problems. Given our changing climate, there has been an explosion of “drought tolerant” and “firewise” plant lists in the gardening world. Most of these lists are devoid of science and all of them are removed from reality. The fact is that taxonomy plays a minimal role in determining whether a plant will tolerate environmental extremes.

Lack of irrigation and mulch guarantees a drought-stressed landscape regardless of the selected species.

Let’s start with the most obvious problems with these lists. The goal isn’t to have plants that require less additional water – it’s to have a landscape that requires less additional water. Similarly, the relative flammability of plants is less important than whether the landscape surrounding those plants is protected from fire. Plants don’t exist in vacuum and unless you are strictly a container gardener a single plant’s impact on water use or fire resilience is negligible. So a gardener’s questions should be “How can I make my landscape more drought tolerant? How can I reduce the likelihood of wildfire damage?” And these are questions that can be addressed with knowledge gleaned from applied plant and soil sciences.

Drought Tolerance

Arborvitae can tolerate droughty summers, but they don’t tolerate improper planting and management.

First of all, let’s think about what “drought” really means: it’s an unusual lack of rainfall. It doesn’t mean no irrigation, and it doesn’t mean dry soil. Drought is a climatological term, not one associated with soil water management. Fine roots and their root hairs require water to function. Without sufficient soil water plants will go dormant or die, particularly during establishment. Plants that are drought tolerant can tolerate seasonal lack of rainfall, but they can’t tolerate chronically dry soil conditions.

Even “drought tolerant” species like Sempervivum will die if there’s not enough soil water.

So we need to look at the landscape factors that allow plants to survive droughts. This includes

  • Root systems that are well established. This means no barriers between the roots and the landscape soil system. Barriers include soil amendments and any materials left on roots during transplant (like soilless media, clay, and burlap). Obviously proper planting is key.
  • Adequate water movement into and within the soil environment. Anything within the soil environment that creates a textural barrier, like soil amendments, prevents water movement. Anything on top of the soil environment that creates a physical barrier, like sheet mulches or compacted layers, prevents water movement into the soil. Sheet mulches include plastics, fabrics, cardboard, and newspaper.
  • Adequate irrigation to support all plants in the landscape. The easiest way to determine whether there is enough soil water is to focus on one or two well-established indicator plants that you notice are the first to show wilt in the summer. That’s when the irrigation should be turned on. For our landscape in Seattle, it was a south-facing hydrangea.
  • Properly mulched soil. Mulch is crucial for soil and plant health, especially in terms of soil water retention and temperature moderation. The best choice for a tree- and shrub-dominated landscape is arborist wood chips. The best choice for arid landscapes is stone mulch – but if this landscape is dominated by trees and shrubs, you need the wood chip mulch. Trees and shrubs, by and large, are not the dominant plant form in arid environments. If you are going to grow plants out of place, you need to include the mulch that matches.
The broad, thin leaves of hydrangeas lose water rapidly and make a good indicator plant for water stress.

These four environmental conditions are key to maintaining a drought-resistant landscape. In terms of appropriate plants, just realize that plants with small, thick leaves lose less water than those with broad, thin leaves. If you want a landscape that conserves water, by all means choose plants whose evaporative water loss is the least.

Firewise Landscapes

Jack pine (Pinus banksiana) produces cones that require fire to open and release their seeds.

I’m not crazy about the term “firewise” as it’s not really a science-based concept. There are natural landscapes that routinely experience fires, and plants native to these landscapes have evolved mechanisms to survive moderate fires. Trees with thick bark, for example, can survive fires that are low to the ground and quick to move through. Other plants may perish in a fire, but leave behind fire-resistant seeds that are able to germinate after the next rainfall. This is not what’s meant by a firewise landscape. Instead, the premise appears to be selecting plants that are low flammability. (Jim Downer tackled this one a few years back but the message just isn’t sinking in.)

Failing trees of any species are more flammable than living trees of any species.

Once again, the focus of this approach is mistakenly directed to plant selection rather than landscape resilience. The best way to reduce the risk of fire is to have a landscape filled with healthy, hydrated plants and a soil protected by the least flammable mulch. The two mulches recommended for drought tolerant landscapes also happen to be the least flammable: stones and arborist wood chips.

  • Bark mulch is hydrophobic and flammable in the landscape.
  • Arborist wood chips are hydrophilic and nonflammable in the landscape.
All wood-based mulches are not created equal.

Despite published evidence that arborist wood chips are not very flammable when compared to all other organic mulches, many governmental groups specifically recommend against them. This is a problem. Stone mulches are great choices IF the plants in question are native to arid zones. Trees and shrubs that are not from arid zones generally require the presence of woody debris to enhance mycorrhizal and root health. Without the proper mulch, these woody plants are less healthy and likely less hydrated than their counterparts under arborist chip mulches. That makes them more, not less, susceptible to fire damage.

A stone mulch in a southwestern desert landscape.

Most of the confusion around arborist chip mulches is probably the result of regulatory agencies confusing bark mulches with wood chip mulches. Bark mulches ARE flammable as they contain waxes and are not great choices for root and soil health. They should be avoided. Agencies associated with fire control methods need to be better informed about the significant differences between these two types of mulches and how they affect plant resilience.

The wildland-urban interface faces the risk of extreme fire danger. [Photo byAnthony Citrano]

And finally, it is important to understand that major wildfires are going to burn anything that’s organic. If you live in such an environment, the best thing you can have in your landscape is no plant material of any sort. A buffer of stone mulch is the only logical option.