Water, Irrigation, Xeric: Related and Essential Garden Vocabulary

The fountain in the Peninsula Park Rose Garden, a frosty February morning

Water, beautiful and essential.  The fountain in the Peninsula Park Rose Garden, a frosty February morning

First in the Water Series

Water is essential to all life on Earth. It comprises a very significant percentage of the mass of every life form. It is the vehicle without which the various metabolic processes would cease. It dissolves and carries in solution the many elements organisms require to build their tissues. It helps produce the conditions necessary for other supporting life forms.  In it’s heating and cooling it creates the weather that helps define the parameters and limits to life in any given place. It works as an erosive medium breaking down landscapes and helping create new ones upon which life adapts and grows. Water moves across and through the surfaces of the Earth in a dynamic yet stable manner helping create the conditions within which life may evolve. It fills that sweet spot moving readily from gaseous form to liquid to solid where our water/carbon based life forms can take advantage of its transformations.  Without it life as we know it would end.  With our disruption, we have altered the pathways and cycling of water across the landscape and so have altered the conditions under which life must live, cutting down forests, draining wetlands, channelizing streams, grading and paving the Earth’s surface. Our actions have directly impacted every habitat, every landscape, on Earth. We are even changing the weather patterns themselves, changing the conditions within which it operates driven by the sun’s energy.  We are massively altering the Earth’s landscapes and its atmosphere in which all of this happens. It is taking on a ‘life’ of its own as we accelerate the rates of deforestation, desertification, expanding urban heat islands, while we continue the mining and burning of carbon previously sequestered for millions of years pressing us on into massive perturbations in our climate patterns. Everything is connected to water.

Errol Creek in SE Portland before it joins Johnson Creek its flow highly modified by us.

Errol Creek in SE Portland before it joins Johnson Creek its flow highly modified by us.

Every region, in fact every site, has a water ‘baseline’. Life responds to it its quality and availability. In a stable natural landscape the animals and plants have been ‘selected’ over time to ‘fit’ within the bell curve it cycles through.   Life adapts or dies, over time populations become stable, but when we alter the landscape on our own particular site or across a region we have changed the conditions within which life must contend. As western peoples our pattern of urban development tends to move our landscapes toward a ‘pleasant middle’ not too wet, not too dry. This is the land we prefer to live on, to build on. Land is changed to create a developable grade, neither too steep, nor wet. We like open site lines and so simplify the landscape creating ‘safer’ places. All of the things that we do tends to move the landscape toward a particular pattern and water movement is inhibited. The soil itself tends to move toward being compacted. Plantings are simplified. A site’s ‘water baseline’ is changed changing what can grow here without our continued intervention. For us in the Pacific Northwest, this ‘water baseline’ shifts downward, there are more and longer periods of drought on a given site. Water is less able to recharge the water table it is carried away during rain events. There is less tree canopy, fewer vertically complex landscapes with deeper organic layers to shade and cool the soil, to hold available moisture and to retain soil nutrients. Life is forced to exist in a thinner layer and we are forced to augment those elements essential to life like water if we insist on growing a plant palette that has often been ignorantly chosen for us. So we water our landscapes, not an inherently ‘bad’ thing to do if we do it selectively and with awareness, but many of us do this out of habit and our practice is ‘wasteful’ especially if it is unattuned to the requirements of the plants in our landscapes.

Applying the Water

For arguments sake, let’s assume we have planted our landscapes with awareness and we are committed to watering them in a responsible manner. The question becomes how much water and how often do we apply it. Beginning in the later 1960’s and ‘70’s it began to be much more common for homeowners to have irrigation systems. If well designed these are much more effective at distributing water uniformly, or where it is needed. Dragging hoses and setting sprinklers introduces much more human error. Sprinkler heads and nozzles are engineered to deliver very specific amounts of water over fairly precise areas if operated at appropriate flows and pressures. Trying to operate more sprinklers than the piping can deliver or doing so at too low or high of a pressure destroys the delivery pattern and with it your ability to accurately deliver water. Too low and the nozzles begin to squirt weakly. Too much and the water begins to ‘mist’ and drift around. Properly designed and operated sprinkler systems will deliver a given amount of water to a set area. Nozzles are rated at specific precipitation rates so a gardener knows that if they run them for ten minutes say, they will have delivered the equivalent of a ¼” of rain, or whatever amount they are rated at.

Problems occur when water is applied at too high a rate and runoff from the site happens. Often times lower flow nozzles can be installed or a ‘cycle and soak’ program can be utilized. Both techniques work, the first by applying water at a lower rate, the other interrupting the application just before the water begins to run off and allowing it time to soak into the ground before another ‘burst’ is applied. There is not one program that will work for any site. It is completely dependent on the system design (the application rate), slope of the site and the texture of the soil. It requires us to look at the rate of application, the soil’s texture which determines how fast the water can move down through the soil and its slope which effects the speed at which water will move across the surface. This isn’t that complicated and with a little experience one can tell very quickly how long one can let the sprinklers run before the water begins to sheet off. You can see it.

There was a problem with most of these old system, which still holds today. People would set up a program, or have one done for them, and turn it on in the spring, at the beginning of the watering season, and shut it off in the fall, at its end. Usually, it was set up to apply more than was needed. This required less of the homeowner. The sprinklers just ran and no adjustments were needed. If it was cooler than average or we had a shower, the sprinklers ran. If it was 100F with low humidity, the sprinklers ran the same amount of time. Client’s yards were kept green. That was the priority. Excess ran off site or percolated down beyond the reach of roots. During cool stretches there were wet patches.

Over time irrigation controllers became more sophisticated allowing for more control. The old mechanical clocks, glorified kitchen timers, were replaced by increasingly sophisticated digital devices. You could ‘bump’ a system up by a chosen percentage, utilize multiple start times, put it on rain delay, choose a cycle/soak option, some have offered rain sensors that would trigger a delay or even have multiple programs to choose from given changing circumstances. Today controllers offer a feature that allows them to work in conjunction with ‘weather stations’, though these are generally for more expensive and only cost effective on larger systems. Portland Parks has been utilizing these for several years in many of its Parks, but no matter what you do, you still have to know the conditions on your site and the requirements of the plants that grow there, because as wonderful as these may be they still have to be ‘told’ what to do and when.

I always keep extra drip tubing around. It is prone to damage by errant shovel strikes. I also keep in stock a supply of fittings to rejoin it, elbows, tees and straight connectors. The tags serve as reminders of the ratings and performance of the tubing.

I always keep extra drip tubing around. It is prone to damage by errant shovel strikes. I also keep in stock a supply of fittings to rejoin it, elbows, tees and straight connectors. The tags serve as reminders of the ratings and performance of the tubing.

I use a drip system at home (These can be prone to vandalism in public places unless they are buried, in which case they are more susceptible to damage by workers because the soft tubing is invisible when digging around.) and then apply extra by hand to help establish new plants or if there are places that aren’t receiving adequate water.

My set up for hand watering minus the hose and my four water spigots placed strategically around the garden to minimize hose use and its consequent plant destruction caused by dragging it around.

My set up for hand watering minus the hose and my four water spigots placed strategically around the garden to minimize hose use and its consequent plant destruction caused by dragging it around.  That’s a brass ball valve acting as a handy shutoff.

This requires different calculations because water is applied very slowly at set points. Application rates are in the very low, in my case, .9 gallons/hour for each emitter. I use ‘Netafim’ drip tubing. Sections of my system are over 15 years old. None of it has failed. The tubing comes with drip emitters installed inside the tube. They do not clog when using our tap water. Tubing can be purchased with emitters spaced at 1’, 1 ½’ and 2’. I chose 1 ½’. One of my beds is 50’long and about 6’ wide making 300 sq.ft. To cover this with an inch (1/12 of a foot) of water (Area x depth, in the same units, equals volume.) takes 25 cu.ft., or, multiplying by 7.4 (there are 7.4 gals in one cu.ft. of water), 185 gals. A quarter inch rain equivalent is about 46 gals. There is 250’ of tubing laid down on it. That works out to 167 emitters. I use a flow valve and can set the number of gallons the valve will let flow through before it shuts off. I have done these numbers for each of my beds, each is on a separate valve supplied by my metering valve (a Bermad). If I used a timer I would let it run for 18 minutes. Each bed is measured and its area calculated. Tubing is measured to figure out the water for each. It may seem overly complicated but you need only do it once.

My beaker of choice that softens and disperses the water flow

My beaker of choice that softens and disperses the water flow.  Exercise some care so that you don’t blow out the screen.

If you use hoses and sprinklers you measure the area they cover and then calculate their application rates by measuring their time to fill a bucket of known volume. You need to know how much water you are applying to a given area, or you are guessing and either under watering or over watering.

How much do I water?

You can subscribe to a City of Portland, Water Bureau, newsletter to get their Weekly Watering Number, the amount of water loss typically in inches over the previous week.  This is the amount you will need to replenish in order to keep your soil water availability up to a level that your plants can ‘pull’ it away from soil particles.  The drier your soil the more tightly the remaining water is to the soil and the less available it is to your plants for their use.  Here’s a link.  This is the combination of losses through evaporation from the ground and ‘transpiration’, water pulled by roots from the soil, through its tissues and out into the atmosphere via the stomata in the leaves. This is a very complex calculation involving daily high and low temperatures, barometric pressure, average windspeed, vapor pressure. latitude, day of the year, solar energy received on a given area and other factors in addition to constants, numbers used to essentially ‘translate’ the calculation into ‘inches’ of water lost. Too much and the water can saturate the upper soil horizon compromising plant performance and even rotting out roots, while gradually percolating down through the profile beyond the reach of roots. Not enough and soil moisture will diminish impairing plant metabolism, resulting in wilt and, if severe enough, tissue and organism death. For the week that I wrote this it is .90”…that’s almost 200 gals on the bed I described above…for the week! This is expected to be another very hot week!  This amount changes significantly…that is what makes programming your irrigation controller once, for an average, problematic.  Early summer, in the 70F range can result in an ET of closer to 1/4″ and of course cooler, more humid and calm in terms of wind, will drop it to 0″.  Over periods that top out over 100ºF this number skyrockets.

Now, you have to keep in mind that not all plants transpire at the same rate. The City’s calculations are based on the typical cool season turf grass, Perennial Rye. This ET is what is estimated to keep your lawn green and growing. If you are keeping a shade garden full of Hostas and other thirsty C3 plants going it may be higher. The leaves of trees on the canopy above can have much more surface area and a much higher water demand than a lawn covering a similar area of your garden, but then their roots penetrate and draw from a much larger volume of soil and therefore of water. If your garden is dominated by drought tolerant C4 grasses (See previous C3, C4 and CAM postings) and similarly matched herbaceous plants and shrubs it will be lower. This is a starting point and will require you to monitor your garden’s performance as you adjust your irrigation practice to find the ‘sweet spot’. A garden full of drought tolerant sclerophyllic plants, such as those associated with California chaparral will have a much lower demand, as will CAM plants commonly associated with desert conditions like Agave, Cacti and their relatives.  It is important that you know your plants and that you group them in beds with others that have similar water requirements. If you don’t it will be more difficult for you to determine how much more, our less, water is appropriate.

I wrote above about a soil’s ability to take water and let it percolate down through its profile. There is another consideration when you find it necessary to irrigate. A lawn is a monoculture, ideally. The plants, all being the same, perform uniformly. Their roots penetrate to a relatively shallow uniform depth. In a typical mixed border as well as a more natural ‘layered’ planting with a tree, shrub and mixed ground layer, there is an overlapping network of roots that, depending on the soil conditions and the plant material, can reach several feet down. Why does this matter? Healthy turf has a shallow volume of soil it depends on for healthy growth, less than a foot. Keeping this layer properly hydrated requires more frequent and shallow irrigation cycles.

(Turf roots, to support healthy, durable turf, also must be encouraged to penetrate as deeply as possible so only wetting the surface layer will not drive them deeper reducing the buffering effect of a larger deeper soil volume. The same basic idea holds for all plants. The ‘normal’ reach of their roots varies and needs to be considered when watering.  This is why, very often, trees can struggle when planted in turf and watering practices are aimed primarily at turf’s needs…The trees, their roots forced to survive in the shallow surface layer must also compete with the turf and maybe subject to drought stress as they have often not penetrated as deeply as they should.  Note that this may not be the same problem in areas that have more normal summer rainfall! where many of our commonly used deciduous trees come from, but here with our dry summers….)

Too much water drives it beyond the reach of roots and with it, the soluble nutrients, like Nitrogen. This is all wasted. The nutrients will gradually move off of site perhaps polluting the water table or area streams unless another plant’s roots are able to draw them up. Keeping the soil profile of a mixed planting adequately hydrated requires fewer/deeper applications for gravity to pull the water down. How you water directly effects how your plants grow. If you have compacted layers below grade, however they may have been created, the percolation down will be inhibited…as will root growth. If you have created ‘artificial layers’ in your profile by adding soil amendments or by repeatedly roto-tilling to the same depth, you have created a plane that will work much the same way. In areas where foot traffic is allowed there will be compaction, which breaks down the soil structure, destroying pore space and the naturally occurring crumb structure of healthy soil, again slowing the percolation of water and root growth. If you maintain your garden with bare soil between plants both rain and the aerial application of water via sprinklers will compact the surface causing water to more likely runoff if there is any kind of slope at all. Mulch helps this. Living plant cover is ideal.

Remember, just because you want to save water doesn’t mean it is a good idea for your garden. If you don’t want to water every summer, plant a garden that will perform well without supplementary irrigation. Stressing plants that are not adapted to such stresses weakens them or will kill them out right. Plants adapt as much as they can given their growing conditions, if you change them mid-stream, after they have established, the changed conditions maybe too great for them. Going ‘cold turkey’ is rarely good for plants. There are too many neglected landscapes in Portland already. Drought is no excuse for neglect. Change your watering practices gradually. Cut their frequency and water deeper so that their root systems develop more deeply. Many plants such as Hosta, Begonia and Impatiens or my Bananas, Cannas and Taro, plants that come from summer wet climates, will never be able to adapt to a xeric landscape in Portland. It is too dry here! There demand for water is too high.  Change out the plants or be prepared to have dead spaces which will fill up with whatever tougher plants are available…very often aggressive weeds which are never far away.

Going Xeric/Forgoing Irrigation

If you do decide to go with a xeric landscape there are several things to consider and remember. These plants still need water! Though often it is much less. You cannot simply plant them and instantly have a xeric garden. All plants take time to develop their root systems and along with them their drought tolerance. Drought tolerant plants utilize multiple strategies:

  1. They transpire less losing less water through their stomata.
  2. Often their metabolisms are different they utilize different metabolic pathways to produce the needed sugars to power cell growth and these can require less water.
  3. Drought tolerant plants often have a protective epidermis, cuticle or trichome structures that reduce leaf temperatures or ‘shade’ the leaf surface reducing the energy striking the more sensitive tissues below making them more tolerant of heat and the intensity of the summer sun, think of the many silvery, fuzzy leaf plants and the hard, sclerophyllic leaves common on many California chaparral and sometimes alpine plants.
  4. They utilize different strategies to access water some by having a very efficient ‘shallow’ root system that can quickly take up water from infrequent precipitation (think Cactus) while others have deeply penetrating roots that seek out water that moves below the surface (think woody Legumes like Mesquite or Desert Ironwood). Some conifers, like Douglas Fir, a very well adapted member of local plant communities, maybe not readily thought of as Xeric, cause water to condense and drip from their needles to the ground extracting moisture that would not have other wise fallen.  Many plants, typically from ‘cloud forest’ regions, are actually able to absorb water through their leaves (this is how foliar feeding of many common vegetable plants works), while typically plants from hot dry mediterranean regions, by guarding against water loss through a variety of leaf adaptations, are equalling ‘resistent’ to absorbing water through their stomata and epidermis as well.
  5. Other plants skip the difficult process of germination and establishment by essentially cloning themselves, doing an end run, avoiding that more vulnerable growth stage all together when they are most susceptible to drought stress.

There will be an establishment period when any plant is more susceptible to stresses even plants that are extreme in their drought tolerance. Brittle Bush, Encelia farinosa, a common member of the Sonoran Desert community, normally experience years, that are so dry that the seedlings that germinate, later perish. This happens in every native plant community. Each has its own baseline soil moisture regime throughout the year that helps determine its plant community. The plants that are adapted to this are xeric there. Desert, Wet Meadow, Tundra, Temperate Forest, Salt Water Marsh…every type presents different conditions. Within the range of normal cycling, young and old plants may succumb while the healthy plants possess the resilience to continue. The line continues. These are xeric. It is the conditions throughout the year of a developing plant, not just for germination, that are essential, that are determinate. Xeric plants tend to be able to withstand the extremes on a site.  This is all part of the selection process in natural landscape communities. Not every plant survives. Some do so spectacularly. ‘Native’ plants may be xeric on a given site. When we plant we are choosing and we may be wrong. When we irrigate we tip the balance toward plants that we choose, not the plants that self selected. When we irrigate we may also be encouraging other plants, weeds, that we don’t want.

When we plant xeric landscapes we should look to such naturally occurring landscapes and plant them in synch with the growing cycle in place, in our case the fall and the onset of rain. Summer in the Northwest is a time of dormancy in many of its landscapes. Seed may be dispersed but it generally waits until temperature and moisture are appropriate. Normally wetter landscapes may see germination and growth in summer, but our cut up and isolated urban landscapes can be quite dry. Xeric landscapes require a different kind of thinking. Whatever we choose to do it is important to be attuned to our sites, the conditions and the plants thereon.

It is important to remember that we are an active part of our landscapes, not unlike the wildlife that may reside therein. Wildlife is not benign in the natural landscape…herbivores and browsers feed upon it directly.  If their populations get to out of balance their impacts can be large and damaging at least until they have expanded so far that there is a population collapse, which relieves the ‘pressure’ on the landscape allowing it to come back.  They are necessary, part of the forces at play…as are we.  It is said that we as humans have the ability to ‘reflect’, to consider what we have done and to change our behavior, forestalling a population collapse of our own.  Ultimately we are dependent upon the landscape, our fate is entwined with it much like the wildlife we ‘manage’.  We build our ‘nests’ now much amplified by our desire, technology and the breadth of materials available to us; we make trails and pathways through them now engineered for uniformity and speed; we consume its water and eat and defecate, only now we feed from a more global pantry and our wastes are processed remotely before returning to selected areas; and in our living here we spread the seeds and propagules of the plants dispersing them to where they might find purchase via our shoes and clothing, the tires of our vehicles and down the ‘paths’ that we utilize. We are animals and we can’t help but play a role…a very powerful role today. We don’t get to opt out. We are left only with the choice of doing so thoughtfully or ignorantly. Doing nothing is not possible. We have changed the face of our planet. We have changed the local availability and quality of water in the landscape. We are part of nature. Nature cannot ‘heal’ itself if we deny our role.

Keep in mind that watering one’s garden need be neither selfish nor wasteful. Healthy beautiful gardens help fulfill our need for food to replenish our bodies, habitat and sustenance for wildlife great and small and beauty to replenish our spirits, legitimate uses for such a resource. A world devoid of beauty, serving only simple direct utility will soon be a dead world. Life must be accommodated. It is vital for us as humans to remain connected to it, that we both understand it and nurture it. I’m providing a link here to a wonderfully written posting by Annie of Annie’s Annuals in California, a region we have all heard or seen and know to be suffering serious drought conditions.


2 thoughts on “Water, Irrigation, Xeric: Related and Essential Garden Vocabulary

  1. Ed Morrow

    An informative and interesting article.
    Here in California we have the California Irrigation Management Information System (CIMIS) that provides the evapotranspiration number for locations all over the state. Fortunately for me there is on just down the road from our house. There is also the Water Use Classification of Landscape Species (WUCOLS), an online list of plants commonly used in landscaping, grouped according to their water requirements in various areas of the state. Between the CIMIS and WUCOLS it’s possible to zero in on the water requirements of almost any plant. You still, however, have to go out and look and stick your finger in the ground to see if you’re doing it right.
    Two questions, if I may. What is the water meter that lets you set the number of gallons that will flow through the meter? On your watering wand, what is the valve that you use? I use a wand and every valve that I’ve used – mostly by Dramm – last only about six months before it starts to leak or not work at all.
    I’ve only recently discovered your blog and am enjoying reading your older posts, and i am looking forward to the new ones.
    Ed Morrow
    Carmel Valley, CA


  2. gardenriots Post author

    Working in the public sector as I did for so many years, we did all of our work internally, not using private contractors. So I can’t really be of much help…However I’ll share the title of a book I bought years ago, 1992, by Robert Kourik, Drip Irrigation: For Every Landscape and All Climates. I found it very well written and easy to understand. It is for the home gardener and does not get overly technical. It served as the base for my own designs and installations. If nothing else it will help you understand and better your chances when working with a contractor to get what you want.



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