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

Rain barrels

A few weeks ago one of our readers, landscape architect Owen Dell, sent me a link to his blog where he takes on rain barrels. It’s a great analysis of the (im)practicalities of rain barrels and it got me to wondering how many of our readers (and my GP colleagues) use these as supplemental sources of irrigation water?

I have two in our back yard that were made from old olive oil containers retrofitted for collecting and dispensing water. They’re hooked together so that when one fills, the rain is diverted to the second.

We use this water pretty much for watering container plants, especially those on our south-facing front porch that require watering every other day during the summer. The barrels each hold 55 gallons and are always full during the winter and spring. We drain them almost dry over the summer, but even a brief rain results in several gallons collected.

So I think they’re a pretty good deal, since we use relatively little water from the hose to keep our container plants happy. But Owen brings up some valid points in his analysis, as do commenters on his blog.

What do you all think?

Keep Calm and Carry On: Part II

Recently I posted that many of the “rules” that gardeners cling to so tightly regarding tree planting (i.e., dig the planting hole 3 times the width of the root ball, always amend the backfill with organic matter) are probably better considered ‘suggestions’ than rules.  While these practices won’t hurt, there are much better ways to spend time and effort to ensure long-term survival when planting a tree.  Here are the top four:

Irrigate.  No matter how much time and effort goes into the ‘perfect’ planting hole; for most parts of the country, trees that are not irrigated after planting are doomed.  Linda advocates watering in several small sips during the week; I still stick to the old school notion of one long soak per week.  In the final analysis, logistics will probably dictate which approach you use.  Either way, the key is to provide trees with water during the establishment year and even into the second year after planting, if possible.

Mulch.  Organic matter placed properly on top of the planting hole will do more good than organic matter placed in the planting hole.  Study after study demonstrates that mulch conserves soil moisture by reducing evaporation from the soil surface, controls weeds, and moderates soil temperature.  Oh, and that business about wood-based mulches ‘tying up’ or ‘stealing’ nutrients from landscape plants?  Maybe for bedding plants, but not for trees and shrubs.  Our research and other studies indicate that, for the most part, the type of organic mulch makes little difference compared to not mulching at all.  Hence, my motto “Mulch: Just do it.”

Proper planting depth.  Width of the planting hole may not matter, but planting trees too deep is a recipe for disaster.  Burying roots too deep reduces oxygen levels around the roots and starts a series of unfortunate events for the tree.   Find the root collar flare and keep it visible.

Bad move.  The contractor was going to install drain tile but decided not to at the last minute to save money. Ouch.

Right tree, right place. In my experience, the number one reason newly-planted trees fail in the first year is lack of watering and aftercare.  After year one, improper tree selection takes the top spot.  Here in the Upper Midwest, poor drainage and heavy soils take their toll year after year.  Lack of water can usually be addressed, but once a tree is planted in a spot that is too wet for that species, it’s usually a long, slow, and agonizing decline.  And it’s amazing how often people will ignore obvious red flags in selecting trees.  Our Dept. of Transportation recently planted 25 eight-foot B&B eastern white pine, which are notoriously salt sensitive, about 30’ from I-96 at a rest area between Lansing and Detroit.  Predictably, after one winter’s exposure to deicing salt spray all the trees were dead or wishing they were dead.  Right tree, right place.  This ain’t rocket science, folks.

Good to the last drop

As part of our discussion of the relative merits of fall planting, Linda mentioned an article in Arboriculture and Urban Forestry that suggests that frequent, light irrigation might be better for landscape trees then the usual recommendation of infrequent soakings.  While I will withhold final judgment until I see the article (I did a scan of the last two year’s table of contents for A&UF but missed the article in question), here’s my rational for following the standard recommendation.

 

First, the context.  In discussing landscape tree irrigation I am talking about watering trees during establishment, typically during the first year after planting and maybe the second if the tree is lucky.  The goal of watering in this case is ensuring survival.  The questions are whether deep soakings are more likely to encourage deeper rooting where water availability is less variable than near the surface after irrigation ceases and whether infrequent watering increases drought tolerance over more frequent irrigation.

 

Roots follow resources
As my Woody Plant Phys students quickly learn, we avoid the teleological ‘roots seek out water’; nevertheless, roots do proliferate where resources are available.  A couple of illustrations.  As a Tree Physiology Project Leader with International Paper I supervised a 25 acre hardwood fertigation trial.   Trees were watered daily via drip irrigation system with emitters spaced every 3’ down a row.  As part of the study we did periodic root harvests.  My technicians quickly learned it was an easy job: just look for the drip emitters – every three feet there was a mop of roots right next to the drippers.  The notion of roots following resources is also widely reported in the ecology literature on tree utilization of ‘patchy resources’ (e.g. Gloser et al. 2008 Tree Phys 28:37-44 ).  Other factors being equal deeper watering should result in deeper rooting.

 

Trees habituate to frequent irrigation
Another short rotation forestry example.  In eastern Washington and Oregon forestry companies Potlatch and Boise Cascade operated intensively managed ‘fiber farms’ which grew 70’ tall, 7” diameter hybrid poplars on a 7 year rotation.  To maintain these growth rates, trees were irrigated daily.  But there was a downside: If one day’s irrigation was missed the leaders to the trees would start to wilt.  Three days without water would result in leaf drop. The daily irrigation was great for growth but it turned the trees into physiological wusses.

 

Periodic water stress improves drought tolerance and survival
A common adaptation for trees to tolerate drought is osmotic adjustment, which is an active accumulation of solutes that enables plant cells to maintain turgor pressure during dehydration.  Plants that have acclimated to stress via osmotic adjustments and other physiological adjustments are able to survive better during prolonged drought than plants that have not been pre-conditioned.  For example ponderosa pine seedlings that had been subjected to brief drought events survived a terminal dry-down two weeks longer than seedlings that had been watered 3 times a week before the final dry-down (Cregg 1994 Tree Phys. 14:883-898.

 

What would it take to change my mind?
Obviously some of my examples here are anecdotal (though there’s plenty of hard data on osmotic adjustment and other drought conditioning effects on trees).  To recommend frequent (2 or 3 times a week), shallow irrigation I would need to see: a well designed and executed experiment that compared frequent irrigation to periodic (once every 7-10 days) applying the same amount of water weekly (0.5 to 1” per week) for the first year and then documented improved survival of the trees after irrigation had been discontinued.  I’m not saying it’s not possible but it goes against my personal observations with irrigated trees in a variety of settings and relevant data with which I’m familiar.

Killing with Kindness

With the advent of Spring comes a myriad of calls on distressed plants from homeowners, nurseries and landscapers.  One of our better tree service companies (I’ll call the owner/operator ‘Mark’ to protect his clients’ identities) in southeastern Michigan called with a series of problems this spring so I decided to take drive over and get a first hand look. We looked at several problems on plants ranging from trees to ground covers but there soon emerged an consistent thread: overwatering.  Plant problems related to overwatering and poor soil drainage are among the most common landscape issues I see year in and year out.  The stops I made with Mark last week were typical. Mark works in several very affluent suburbs around Detroit (I know readers around the country don’t associate Detroit and affluence, given our recent press, but there is still some serious money in the area).  Some of Mark’s clients spend up to $20,000 per year just to maintain the trees and shrubs on their property – that’s not including lawn maintenance.  Needless to say, these folks want everything perfect.  In their effort to have their landscape look more perfect than the neighbors, the homeowners and their gardeners often go overboard – especially with irrigation.  One of the things that caught my attention during our site inspection was recurring issues with Norway spruce.  For the most part, we regard Norways as a cast iron plant and one of the last trees with which we’d expect to have problems.  Yet we saw several instances were established specimens were suffering needle die-back and declining.  


In each case the trees were irrigated in situations where they would likely grow well without supplemental watering.  But the trees were surrounded by ground covers or annual beds with heavy soils that were heavily irrigated.  Problems usually increased on down-slope positions.  


The solution?  Back off the irrigation.  Everyone knows trees need water, but roots their roots also need oxygen.  At one site we visited, the homeowner already had his gardener running the irrigation system – in April!  This is truly killing with kindness.  Most established landscape trees, shrubs and perennials  in this part of the world need little, if any, irrigation.  Newly planted trees and shrubs need an occasional (weekly to bi-weekly) drink in the first year and some follow-up the second year.  After that they can manage most years on our rainfall. In the end, a lot comes down to design.  Establish thirsty annual beds where they can be irrigated without drowning hardier trees and shrubs.

Another look at TreeGators

Following up on Linda’s earlier comments about potential problems with TreeGators, my summer interns and I did a random spot check of about 150 TreeGators currently in use on the MSU campus.  As background, MSU Landscape Services plants about 1,200 trees and shrubs each year.  All newly-planted trees which are not on an automatic irrigation system are fitted with one or two TreeGators, which are filled from a water wagon every week or every two weeks, depending on weather.  Conifers and multi-stemmed trees are fitted with Tree-Tubes, another style of irrigation bag that fits like an inner-tube around the base of a tree.  At MSU irrigation bags are usually left on trees during the first growing season.  Presnetly there are over 1,000 irrigation bags in use on the MSU campus.

During our spot-check, we found few items I would consider to be a major concern.  We found 25 trees with mold or saprophytic fungi growing in the mulch under the bags.  While unsightly, these are unlikely to cause major tree problems and will be gone once the bags are removed and the mulch is exposed to air.  All but a handful of the bags had drained properly and therefore the trunks on most of the trees were dry – eliminating the potential problems that Linda noted about the trunks remaining constantly wet.  TreeGators are designed to drain in 4-5 hours.  Therefore, on a once every two weeks or once a week filling-cycle, they should be full only 1.5% to 3% of the time.  TreeGators that are not draining between fill-ups should be checked for clogs and have a new hole punched, if needed.

It is worth noting that the dark protected space between the irrigation bag and the trunk can provide habitat for various organisms.  We found an assortment or earwigs, spiders, and millipedes; plus one tree frog and one dead bird. The major concern that we found, however, were gypsy moth egg masses (photo 1), which occurred on 14 trees.  Gypsy moths, which are serious defoliators of trees in the eastern US, like to lay their egg masses in protected locations on tree trunks so the inside of the Gator bags makes a handy hideout.  Once found, egg masses are fairly easy to remove, though killing the eggs takes some effort.

While there is a potential for pests to hide out under irrigation bags, I think the benefits of irrigating with TreeGators outweigh the potential negatives. This is especially true in our heavy Midwestern soils where it is impossible to deliver any meaningful amount of water to a newly planted tree in a reasonable time without run-off.   MSU Campus Arborist Paul Swartz reported less than 0.5% mortality out of over 1,000 newly planted trees on campus last year.  The high success rate is attributable to good overall tree management by Landscape Services, including supplemental irrigation using the irrigation bags.  The take home message from our survey is that tree care workers need to check bags at each filling to ensure that bags are draining properly and to lift up the bags and inspect for signs of pests or other issues.


TreeGators on MSU Campus


Tree frog inside TreeGator


TreeGators should drain in 4-5 hours when working properly.


Cause for concern.  Gypsy moth egg mass on trunk.