Watering tips for your Tucson garden

Maintaining your drip irrigation system

Drip irrigation systems are probably the most efficient for our climate, but they do require some periodic maintenance. It’s pretty easy to do this maintenance yourself, and it won’t take long. It will help ensure that your plants are getting the water they need, and that you’re not wasting any water due to leaks and non-functioning emitters. To make your maintenance easier, don’t plant any delicate, large or spiny plants near the valve box or your water meter, and move or trim back any such plants if they are in your way.

If you’re unfamiliar with the components of a drip system, check out my article “Irrigation tips for desert gardens.” The first thing to do is to run your drip system and walk the entire length of it, making sure each emitter is going to its appropriate plant and working correctly. You can get a gist of whether there is any blockage as it's running by looking at how quickly the water drips out of the emitter or the microtubing. While you’re doing this, keep an eye out for missing emitters, chewed microtubing, or tubing going to the wrong plant.

You will want to repair any issues you see. Most hardware stores sell repair kits, and specify which systems they work with. Make sure you know the size of your supply tubing. This is the black or brown PVC hose that’s usually called ½ inch; however it comes in various outside diameter sizes (0.620 inch, 0.700 inch, and 0.710 inch) and your fittings need to match the size you have. If you’re not sure of the size, you can take a small sample of it with you to the hardware store to see what fittings match it. Your supply tubing may also come in other sizes but the so-called ½ inch is most common. Check out this resource to learn more about drip irrigation tubing sizes.

Keep in mind that the standard 1/2 inch PVC tubing shouldn't run more than 200 feet from the water supply line, and should not have more than 200 gallons per hour of flow installed in it. This is called the 200/200 rule. If you break this rule, your system will have too much friction in it, which will prevent consistent water delivery. You may see plants that don't thrive because they're not getting consistent water flow.

Fortunately, the microtubing is pretty standard 1/4 inch (although it also comes in ⅛ inch). It tends to be more flexible and easier to work with than the supply tubing. Some other items you may need to fix your drip system include PVC cutting tools, extra drip emitters in various sizes, and goof plugs (for fixing mistakes and getting rid of drip lines to plants that no longer need them). All of the PVC products are easier to work with if they’re warmed up, but if they’re left out in the sun they get really hot.

Once you’ve done the walk-through and fixed any obvious issues, the next step is to check your filter. This is found in the valve box. Make sure to check the valve box carefully for critters before reaching in. Snakes, scorpions, and other biting animals may be hiding in there because it’s cool and dark.

The filter compartment is usually sticking out towards you and is unscrewed from the plumbing in the valve box. Most filters are metal, and can simply be hosed off. When you have the filter off, you can flush the system out with your garden hose. This is good practice anytime you do repairs on your system, to ensure that soil and other particles haven’t gotten into the system. During the flush, walk around again and make sure all emitters are working. Replace your filter after cleaning and flushing, and replace the cover on the valve box.

While you’re checking your valve box, look for any signs of a leak. You can also see if there’s a leak by checking your water bill carefully and comparing your bills from the same time period last year. Also look for any rapid or steady increases in your water usage that you can't explain. The City of Tucson has a handy page that explains how you can use your water meter to detect leaks.

If you’re concerned about the efficiency of your irrigation system, you can request a water use audit from Tucson Water. They will evaluate all of your appliances and check your indoor and outdoor water usage, then make suggestions on how you can be more water efficient. Keep in mind you can always supplement your backyard irrigation with grey water and rainwater harvesting.

Harvesting the Rain Part 1: Passive rainwater harvesting

Spring is a great time for planting, but those plants you just bought will need water to get established and to survive. This means spring is also the perfect time to think about rain harvesting in your yard or home.

Rainwater harvesting is either passive or active. In passive rain harvesting, your soil is the storage medium for the rain, while active rainwater harvesting involves the use of tanks, gutters and similar equipment.

Passive rainwater harvesting is the cheapest — you don’t need to spend money on tanks and you can do the work yourself. This article is the first of two and will discuss passive rainwater harvesting, while the next newsletter will focus on active rainwater harvesting.

Harvesting the rain has many advantages. For one, it will reduce your water bills by utilizing free water for your landscape plants. Rain is the best type of water for plants, as it helps flush salts and minerals through the soil. In this respect, it is far superior to irrigation with treated water, which actually concentrates salts and minerals in the soil, contributing to caliche development.

When done correctly, rainwater harvesting can also eliminate water erosion on your property and help with flooding. In addition, in urban areas, containing the water that falls on your property can greatly help reduce the runoff of water in the streets — a huge source of water pollution in our ephemeral rivers and streams.

Despite being a desert, our Sonoran landscape gets a decent amount of rain most years. We have two rainy seasons: the summer monsoon and the winter rains. In total, we get an average of 11 inches of rainfall per year. That may not sound like much, but over a 6,000 square foot yard (a little over a tenth of an acre) that adds up to about 40,000 gallons per year of free water.

The basic idea behind passive rainwater harvesting is that you shape and contour your soil to maximize water collection and infiltration. You create structures from the soil and rocks (called earthworks) to channel the flow of water where you want it. Thanks to gravity, water will always flow downhill, so you can shape the soil so that the water flows along a certain path and into basins where it will infiltrate and water your plants.

One very simple example is building a depression around a newly-planted tree. When it rains, water will flow into the depression and collect there, allowing it to infiltrate into the soil rather than running off. Mulching the depression will help prevent evaporation of the water and is a key step in rainwater harvesting.

Other basic water harvesting earthworks are berms (basically little hills, usually 6 inches or less in height) and basins (also called swales). To create these, scoop out the soil from an area you want to collect the water (the basin) and pile the soil on the downhill side like a little fort (the berm) to keep the water from running off.

You can also construct terraces, rock dams, gravel drains and various other earthworks to channel your rainfall. Which earthworks you use depends on the slope of your land, how fast the water flows across it, and how much of the water you want to harvest.

Another key aspect of passive rainwater harvesting includes the use of landscaping materials that are permeable to water for your hardscape areas. Brick pavers, for example, allow water to infiltrate between their edges, while a solid concrete deck or asphalt driveway does not. Permeable hard surfaces help to prevent water runoff, which ends up flowing down our streets causing flooding and washing oil, gasoline and other pollutants into our rivers.

Since passive rain harvesting only involves moving soil and rocks, it can be a DIY project if you need to save money. It can be a lot of work, though, particularly if you are doing it all by hand. The City of Tucson has been offering a rebate for homeowners installing rainwater harvesting systems since 2012, so you can check out the website for more information. If you would like help designing or installing a rainwater harvesting system, local nonprofit Watershed Management Group provides those services.

It can also be difficult to create an extensive passive water harvesting system if you have a lot of existing vegetation that you want to keep. You don’t want to damage tree and shrub roots, for instance, while excavating your earthworks. In situations like this it is usually best to pile berms around the drip line of the plants rather than to dig in the vicinity of the roots and risk harming them. You can also dig small basins around the existing plants — don't worry, the roots will find the water. Using a lot of mulch can also help you conserve water in your landscape — make sure you mulch your basins, too!

The other downside to passive rain harvesting is that you only have the water when the rain falls. You can spread out the benefits of it over time by using mulches to prevent water evaporation from the soil. Sooner, or later, though, our hot sun will dry out the soil. To keep using the free rain, you will need tanks to store the water over a long time period. This is active rainwater harvesting.

Resources to get you started:

• Brad Lancaster, a Tucson native, has two excellent books which are considered the definitive texts on rainwater harvesting. He has a website where you can purchase the books (Volume 2 focuses on passive harvesting) and check out lots of free info on harvesting the rain (and a lot more). You can also take a drive down to the Dunbar Spring neighborhood, where he and his neighbors have installed a number of passive rainwater harvesting features to collect street runoff.
• The LEAF Network’s basic rainwater harvesting information. A good resource to get you started.
• The City of Tucson’s guide to rainwater harvesting. You can download this as a PDF. It has very helpful graphics showing the different types of earthworks. 
• Pima County's guide to rainwater harvesting. 
• Rainfall calculator from the U.S. Geological Survey. You can use this to calculate the number of gallons that falls on a given area.

Harvesting the Rain Part 2: Active rainwater harvesting

Active rainwater harvesting involves the use of gutters and tanks to channel and store rainwater. This allows you to “bank” rainwater in our unpredictable climate so you can stretch out the period of time rainwater is available for irrigating plants. It is usually used along with passive rainwater harvesting to maximize the amount of rain you can use in your landscape.

Rainwater is best for plants, because it doesn't contain the minerals present in our irrigation water which over time add salts to the soil. Rain flushes those salts out, and also carries some nitrogen and other nutrients as well as microbes present in the air. If you have any non-native plants in your garden, they would definitely benefit from occasional deep watering with rainwater.

If you have the space and budget, you can purchase large water tanks or set up a system of your own using recycled food-grade barrels, trash cans, storage containers and the like. Water tanks come in many different sizes and configurations, so chances are you will find a combination that will fit in the space you have. Water tanks can be set up individually or can be connected in a series. If you have a limited budget, you can start with one tank then add others as budgeting and space permits.

The first step to figuring out your active rainwater harvesting system is to walk around your garden to get a sense of the space you have, the locations where you may want the tanks (ideally close to plants that require irrigation) and to see if the tanks can provide any other services for you. For example, tanks can also double as hardscaping features to provide shade, privacy, sound blocking or vertical space in your garden. You will probably want to place the tank in an elevated position on your landscape — this can obviate the need for a pump, as gravity will help the water drain out of the tank. The higher the tank is relative to the irrigation area, the farther the water will drain.

The next step is to calculate the roof area that you will be harvesting water from. Don’t worry about the vertical slopes and angles of your roof — just look at your property on Google Maps and use the measurement feature to estimate your roof area. Once you have that number, multiply your roof’s square footage by 0.62. This will give you the total number of gallons you can expect to harvest per inch of rain. You probably don’t need tanks to hold more than 1-2 inches of rainfall since our largest storms rarely exceed 2 inches of rain. If you have the space and budget you can put in as many tanks as you want.

To determine how much water you may want to harvest and store, figure out what plants you want to grow and calculate their yearly water needs. Brad Lancaster’s website has helpful charts which list the yearly water requirements of many plants. His books on rainwater harvesting are considered the definitive resource by many around the globe. When looking at the chart and choosing plants, keep in mind that plants that are winter-deciduous, such as fruit trees, will not require much water during the winter months, so they may not be as water-intensive as they seem.

A number of companies in town can help with designing and installation of active rainwater harvesting systems. Watershed Management Group can design a system for you, as can Eco Sense Sustainable Landscapes and Southern Arizona Rain Gutters. If you want help with gutter installation, companies such as Gutter Systems of Southern Arizona can help as well.

The City of Tucson offers rebates for homeowners installing rainwater harvesting systems. You must be a City of Tucson water customer and attend an approved workshop on rainwater harvesting. These workshops are provided by Watershed Management Group, Sonora Environmental Research Institute and intermittently by the Pima County Cooperative Extension. 

More resources:

• City of Tucson Rainwater Harvesting Guide
• Handbook: Harvesting water for landscape use

Grey water: What is it and how do you use it in your garden?

In our desert, water is precious. Many gardeners look for ways to reduce their city or well water use, including rainwater harvesting and planting drought-tolerant plants.

Did you know that you can also use some of your home’s wastewater to water your garden? Nearly a third of the waste water in your home comes from showers, bathroom faucets, and laundry, and is called grey water. Water from toilets, dishwashers, and kitchen sinks is considered black water and cannot be used for irrigation.

Grey water can be reused on most plants. The only exception is that you shouldn’t use it for your vegetable garden; however, it is safe to use grey water on any tree, including fruit and nut trees, as well as ornamental plants. Because grey water contains detergents, bacteria, bits of clothing, and other waste, you cannot store it in tanks like rainwater; it would become foul-smelling and a site for bacterial and algae growth. It must be drained into your soil within 24 hours of being produced. 

For a simple system, you may want to build some basins around your plants to hold the water and keep it from causing any erosion in your yard. If you need a more complex system, you may choose to use a surge tank and pump, which stores the water very briefly and pumps it out into your yard at a rate which won’t cause erosion. This type of system can also be connected to drip irrigation, which is the most efficient way to water your plants. Keep in mind that if your grey water setup uses a pump of any sort, it must have a reduced pressure assembly  to prevent the grey water from backflowing into the main water supply.

Once you have a system installed, you will need to monitor the ingredients in the soaps, shampoos and detergents you use to avoid harming your plants. Brad Lancaster has a great guide on which ingredients to avoid on his Rainwater Harvesting website. Some ingredients to avoid putting into your grey water include bleach, peroxide, borax, parabens, and petroleum products. To keep these substances out of your garden, make sure any grey water hookup in your laundry room has the option of diverting the wastewater into the sewer so you can run the occasional bleach load if needed without harming your plants.

The City of Tucson offers grey water harvesting rebates to help you pay for the changes to your plumbing.  First, you will need to take a free two hour class with Watershed Management Group which will teach you about correctly setting up, using and maintaining your grey water system. You can then set the system up yourself, or hire someone. If you want to start with something easy, Watershed Management Group has laundry-to-landscape kits as well as classes to help you install them; they can also install the kits for you.

If your system is connected to drip irrigation, you will need to check it a couple of times per year to look for clogging. There are plenty of local guides available to help you with the installation and use, including a thorough guide from the City of Tucson as well as lots of helpful information on Brad Lancaster’s Rainwater Harvesting website.