Water Wise Gardening: Conserving and Irrigating Responsibly

While we can’t ever control or even predict the weather, in most places it is important to have a plan on how to deliver water to our home gardens during the hot, dry months of the summer.  Aside from reducing water need through some good management practices, delivering water in an efficient and sustainable way is important when planning and planting our home gardens. 

When there is scarcity, it is necessary to conserve. Several years I got to see scarcity in person on a sustainable agriculture tour of New Mexico.  Farmers in New Mexico have only limited access to water from irrigation canals, to flood irrigate their fields, or even wells for drip irrigation.

This severe lack of water got me thinking about how much we take water for granted in our own gardens.  We often apply as much as we want or need in an inefficient manner (using sprinklers, sprayers, etc.) because we think it will always be there when we turn on the tap. 

Where I’m located in Nebraska we are also blessed to have water falling from the sky. Sometimes there’s too much, and at others there’s not enough. But that’s much better than in some places – I visited some parts of New Mexico on a farm tour where they get seven inches of rainfall in a normal year. Seven.  Total.

Thinking about conserving what water we have means that we are good stewards and are ready for when issues do arise. And let’s face it, there are some times in the summer that are dry where water conservation will help reduce using water, which can also save money.

When we talk about conserving water, there are two ways to go about it. First, look for ways to reduce the need for water. Then, look at ways to reduce water waste and usage whenever you need to use water on your lawn, landscape or garden.

Reducing the need for water

During dry times, it can be necessary to provide water to the garden to keep it growing healthfully along. However, there are many ways to reduce water loss or increase the amount that stays in the soil around the plants.

Mulching not only reduces weeds, but also helps hold moisture in the soil. Having one to two inches of mulch on landscape beds can reduce evaporation from the soil and decrease the amount of water you need. Newly planted trees should be mulched for the first few years to help hold moisture in the root zone as well.

Mulching is also important in the vegetable garden. Using straw or shredded newspaper are simple ways to conserve moisture, beat weeds and even reduce diseases. Note that this is shredded newspaper used on top of the soil for a mulch, not whole sheets applied below another mulch or on top of the ground.  That process is called “sheet mulching” and we typically don’t recommend it here at the GPs because it limits air movement into the soil and can disrupt the soil microbiome. Stick only to shredded newspaper as a top dressing. (See the bottom of the article for journal articles discussing paper and straw mulches).

Shredded newspaper in my tomato bed. There are 2ft woodchip mulch walkways between 4ft wide beds.

You can use woodchip mulch in the vegetable garden, but it can be difficult to manage when you are frequently planting, replanting, or harvesting crops.  If you accidentally incorporate it into the soil, it can tie up nitrogen available to plants and cause deficiencies.  As long as you are good at keeping it on the surface, it isn’t as much of an issue.

Large scale gardens or farms make use of black plastic as mulches to do much the same thing. Plastic mulches are typically beyond the scale needed for home vegetable gardens and have their own set of drawbacks such as limiting water and air movement, but for those struggling with difficult weeds or with issues limiting manual removal (disability, limited movement, etc) it may be explored for smaller scale production. There are now even biodegradable plastic and paper mulches available. Use of these does require drip irrigation beneath the mulch, as rain cannot penetrate to the root zone. With the issues associated with them, plastic mulches would be considered a last resort for all but the largest home vegetable gardens, and many of my GP colleagues recommend against them for all home garden situations – but they can have their very limited place in the home garden toolbox.  And we definitely recommend against the use of plastics and landscape fabrics in ornamental beds and landscapes.   

Choose plants that require less water. There are many plants available that have lower water requirements. Ornamental grasses, Liatris (blazing star), Kniphofia (red hot poker) and sunflowers come to mind. Most native plants are commonly thought to have lower water requirements, but this isn’t always the case and natives may not thrive in altered ecosystems (urban settings or even managed landscapes). Most bulbs also are water efficient and do not require extra watering, as are most culinary herbs.

Mowing less often in the hot and dry summer also can conserve water if you are one who waters the lawn. I’m not a big fan of watering lawns, since it is such a large water usage, but I know there are those who prefer to have their lawns lush and green at all times. Instead, when the summer gets hot and dry, leaving the grass on the taller side can help it stay green even without water. Many of the grasses we grow here are cool-season and go semi-dormant in the heat. Stopping mowing when the heat starts slows down growth and the need for water.

Irrigating Efficiently with Drip

When it comes to getting water to the garden, there are definitely more efficient ways to make it happen.

Unfortunately, the most common method — using sprinklers — is also the least efficient. It is hard to direct the water to the right place, and during periods of high heat evaporation takes up much more water than you think. But there are ways to get water to your thirsty plants without running up the water bill.

Drip irrigation is probably amongst the most efficient and sustainable ways to water your landscape or vegetable garden. This method allows you to apply water directly to plants in a controlled manner, rather than spraying an entire area with water.  Also, since the water is applied directly to the ground rather than sprayed through the hot summer air, the water is much less likely to evaporate. 

Drip irrigation tubing. Each drip opening emits on this version emits 1 gallon of water per hour.

There are a few different types of drip irrigation systems available.  Probably the easiest to install is a drip tape system.  This is a deflated tape that already has water-emitting slits cut into it.  While each slit applies a precise amount of water over a given time period, the pre-determined regular placement of the slits makes this system better for plants grown in rows, like vegetables, rather than landscapes where plants are of differing sizes and spacing.  And while it can be used for vegetable gardens, probably the easiest system for a landscape would be one where there are tubes you can cut to various lengths and insert controlled drip emitters at customized locations.  Another use for this type of drip irrigation could be for containers on a porch or deck – you can easily run the tubing out of sight along a bannister or railing and direct individual emitters to individual containers.

It all sounds complicated, and larger systems can be, but there are small and simple kits you can easily find at many garden centers or online retailers available for home gardeners to install their own within a matter of hours. You will need to have some skill at reading directions to install them, but the process is pretty simple. 

For information on setting up drip irrigation for your home garden, check out these great resources from Extension institutions across the country:

Drip Irrigation for Home Gardens

Building and Operating a Home Garden Irrigation System

DRIP: Watering the Home Garden

Soaker hoses are a similar concept to drip irrigation, but instead of small drips these hoses just emit water all along the hose. Still better than sprinklers, these hoses are quite a bit less efficient than drip, since you can’t direct the water exactly where you want it.  They are also easy to apply too-much water to an area since they can emit large volumes. Installation is pretty simple, though, since you just lay the hose down where you want it.

One great benefit of both drip irrigation and soaker hoses is the application of automation.  Using a timer can make it easy to keep the garden watered through the season. Timers can be as simple as a dial to manually run the irrigation for a specified time or fully automatic to run the irrigation for various lengths of time on different days of the week.  Some more advanced timers also have rain sensors or soil probes to reduce or avoid running when rain makes watering unnecessary (if you don’t have a sensor, remember to stop automatic running until the soil has dried).  And in today’s emerging technology, there are also timers or flow controls that can be automated or controlled from a phone app.  The timer that I’m now using at home connects to my Wi-fi, and in addition to allowing me to control and observe the watering status from anywhere in the world, connects to local weather data to automatically set a “smart watering” schedule taking into account rainfall, temperature, wind speed, and other factors. 

My fancy water timer.

Another effective way of providing water to your garden is through water catchment.  Water catchment is just a fancy way of saying that you use a rain barrel. Here you are collecting rain runoff to use in place of water from the tap. There are some ultra-low-flow drip irrigation systems that you can use with rain barrels (if they are raised high enough to get water pressure), but this use is usually for watering by hand. For larger gardens, the large IBC totes that hold 200 or more gallons can make good water catchment barrels.  Just make sure that if you are using them (or any other barrel) for fruit or vegetable production that they are made of food-safe plastic and their previous contents were also food safe.  (Check out our guide on Building a Rain Barrel)

Selected references:

Comparisons of shredded newspaper and wheat straw as crop mulches

Soil Temperature, Soil Moisture, Weed Control, and Tomato (Lycopersicon esculentum) Response to Mulching

Newspaper Mulches for Suppressing Weeds for Organic High-tunnel Cucumber Production

Planting Prognostication: Understanding last frost and planting dates

Except for areas of the US that are more tropical like southern Florida or Hawai’i, most gardener’s planting schedules are set around winter weather and the possibility of frost or freeze.  And even for gardeners in those more tropical areas, planting sometimes needs to be planned to schedule around the extreme heat of summer.  Understanding these planting times can really lead to success or failure, especially for vegetable gardens, tender annuals, tropicals, and non-dormant perennials.  There are a few tools that help us understand weather patterns and predict critical temperatures for planting, namely the USDA Hardiness Zone map and the Average Last Frost/Freeze dates.  The USDA Hardiness Map shares data on what the average coldest temperature is, which is key for selecting perennial plants that you want to survive the winter.  However, to know when to plant we look at the average freeze and frost dates.  There seems to be a little bit of mystery, and even confusion, around the dates and how to interpret them, so let’s take a little time to understand them a little better.  And since my background is in vegetable production, I’ll share a bit more detail there in terms of plants – but you can translate the information to ornamentals, especially those that are frost tender pretty easily. 

Understanding Average Last Frost Date

What is the average last frost date and how is it figured?  The average last frost date is exactly what it says it is – the average date at which the probability of frost has diminished.  Just how diminished really depends on the source, so we’ll follow up with that in a bit.  The data is computed by NOAA (National Oceanographic and Atmospheric Administration) and the National Weather Service to determine the probability of temperatures relating to frost and freezes based on weather data for an area over the last 30 years.  They compute the likelihood of a light frost (36 F), frost/heavy frost (32 F), or freeze (28 F) at three different probability levels – 90% (the temperature is very likely to happen), 50% (the possibility is 50/50), or 10% (the temperature is unlikely).  This tool from NOAA provides a chart with probabilities for locations throughout each state.  

This data is typically collected and analyzed every ten years or so.  I’m not exactly sure when the last data was analyzed, but I did find some maps on the NWS referencing the period 1980/81- 2009/20 (below).  Therefore it is likely that new data will be released either this year or next year.

Temperature hardiness of common vegetables

Awareness of tolerance is especially important for vegetable crops, as the growing season and expected productivity of the plants.  The following chart is a general guideline, and your mileage may vary based on cultivar difference, microclimates, and other factors.  Also note that these temperatures are for both planting in spring and fall kill temperatures.  Some of the more tender plants, like tomatoes, may withstand colder temperatures when they’re mature so they may be less susceptible to frost at the end of the season vs. the beginning of the season. 

Season extension techniques, such as row covers can be used to protect tender plants in the spring and extend harvests in the fall.  Row covers can be selected by the degrees of protection they deliver.  For example, a row cover may offer 4 degrees of protection.  This allows the protected plant to withstand air temperatures 4 degrees colder that what it would unaided. For fall crops, note that plants may stop growing well before the kill temperature but will hang out in “stasis” until they are killed. The above NOAA chart provides probabilities for both spring and fall – allowing you to not only plan for spring planting but also for fall crops.  For scheduling fall crop planting dates, find your first frost date, count backwards the days to maturity (from the seed packet or tag), and add a few weeks for a harvest window and for the slowing growth as temperatures drop.

The Problem with Probability

These probabilities are based on past weather data, so keep in mind that these dates are used as a prediction not as a guarantee.  It is especially important to remember this as weather uncertainty increases with climate change.  Last frost could occur well before or even well after these predictive dates.  This also begs the question – which probability should you use?  Looking around at different sources, you might find sources that use either the 50% or 10% probability statistic, and there seems to be a bit of disagreement as to which one should be used.  Based on the data for my region, I’ve seen sources share both dates.  It really comes down to how much of a gamble you want to take or how much you want to push up harvest or maturity.  If you plant on the earlier 50% probability date you may end up having to cover the plants a few times to protect them from frost.  But each day that passes means that the chance of frost or freeze decreases.

Whenever I give a talk here at home in Omaha, I often ask my audience to guess what the average last frost date is for planting.  Invariably, the answer I get is Mother’s Day…which I guess works as a guidepost in general.  However, looking at the data (below), we can see that the 10% probability date for a 32 degree (killing) frost is May 4.  The light frost date is May 11 – plants may be damaged but not killed unless they’re very tender.  And the 50% probability date for a killing frost is actually April 21, which is the point where the probability of frost is 50% each day (and the probability shrinks each day.

Sometimes produce growers may opt to go early to get vegetables to market – which extends the sales season and allows them to charge a premium price if no other growers are selling.  Season extension techniques like high tunnels have also pushed back farm production dates.  As climate change makes weather more unpredictable, we may all be finding ways to alter the growing season as a norm rather than an exception.  Until then, we’ll rely on the data we have to make the best predictions.   

Sources:

https://www.canr.msu.edu/news/freeze_damage_in_fall_vegetables_identifying_and_preventing

http://www.gardening.cornell.edu/homegardening/scene0391.html

https://www.weather.gov/iwx/fallfrostinfo

https://www.ncdc.noaa.gov/cgi-bin/climatenormals/climatenormals.pl?directive=prod_select2&prodtype=CLIM2001&subrnum%2520to%2520Freeze/Frost%2520Data%2520from%2520the%2520U.S.%2520Climate%2520Normals