Amanual about rainwater harvesting in NewMexico would not be complete without a

discussion of the basic principles and techniques ofwaterwise landscaping (also known as drylandlandscaping or xeriscaping). By applying waterwiseprinciples to your landscape, you will not only getthe most out of the available water supply, you willalso enjoy the beauty and diversity of native andother low-water-use plants.

The term xeriscape is derived from the Greek wordxeros, meaning “dry.” The goal of xeriscaping is tocreate a visually attractive landscape that usesplants selected for their ability to thrive in localclimates. In New Mexico, this means using plantsthat can grow with very little (or no) water, otherthan what nature provides.

There are seven basic principles of xeriscaping anddryland gardening:

1. Planning and Design. A beautiful xeriscape startswith a good design. The physical characteristics ofthe site must be considered, as should your needsand aesthetic preferences. The design of alandscape, especially a roof-reliant landscape thatincludes a cistern system, is such an important topicthat Chapter 4 delves into it in detail.

2. Soil Improvements. New Mexico’s soils typicallylack the organic matter necessary to providesufficient plant nutrients and water retention.Native plants tend to need less organic matter thanadapted plants, but most plants benefit from theaddition of some organic matter, such as compost,into the soil.

Compost helps sandy soils retain water and helpsclay-dominated soils drain faster. When water mixeswith compost in soil, the resultant carbonic aciddissolves the 18 essential elements typically found incompost so that plant roots can more easily take upthese nutrients. Compost also aerates the soil sothat plant roots can maintain their optimalmoisture content. In these improved conditions, theinsects, microorganisms and mycelium found inhealthy soil can thrive, so plants can establishthemselves quickly in the landscape.

Perhaps you have already been diligently makingcompost with your kitchen scraps and yard waste ina convenient, shaded and wind-protected corner ofyour garden. Maybe you’ve even added rabbit,chicken or horse manure, or some other source ofnitrogen to your compost pile. Chances are,however, that you may need to either importcompost (to mix into your existing soil) or bring insome premixed topsoil.

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Chapter 1: The Fundamentals of WaterwiseLandscaping

Planning and Design

Soil Improvements

But don’t give plants (especially native plants andother plants that like “lean” soil) too much of agood thing. Roots pampered by too-rich soil arelikely to be stunted when they grow to the outeredges of the imported soil and hit the hard edge ofexisting native soil. Those pampered plants will notbe as hardy, particularly in drought or precipitation-only conditions.

Smart roof-reliant landscapers understand that thebest time to complete the soil-building part of theproject occurs when cistern excavation equipment isonsite, particularly when installing a new landscape.With impressive efficiency, a backhoe can oftenhandle much of the excavation, importation andmixing processes of soil improvement. Heavyequipment can also efficiently remove layers ofcement-like caliche, which sometimes plague NewMexico’s soil.

If it is not practical to use heavy excavationequipment to mix compost into your soil, considerrenting a jackhammer to loosen up hard soil.Rototillers are also helpful when mixing compost andother organic matter into the soil.

3. Appropriate Turf Areas. Xeriscapes in New Mexicotend to minimize turf areas because traditionalKentucky bluegrass lawns are not native to our desertand dry mountain climates, and they use prodigiousamounts of water. Small turf areas, particularly thoseusing drought-tolerant grasses such as buffalograssand blue grama, can provide appropriate play areasfor outdoor activities. However, it is notrecommended to use cistern-based systems to irrigateturf areas, so this roof-reliant landscaping manualdoes not deal with lawn applications.

4. Low-Water-Use Plants. Choosing appropriateplants for your local area and for the specificconditions on your property is a key element increating a roof-reliant landscape. For example, therange of waterwise plant options near Red BluffReservoir (elevation just under 3,000 feet) insouthern New Mexico is very different from theplant palette for the village of Truchas (elevationjust over 8,000 feet) in northern New Mexico. Localplant nurseries, landscape designers and otherlandscape professionals, horticulturists, native plantsocieties, local master gardeners and countyextension agents can be invaluable resources forinformation about the types of plants that areappropriate for your landscape.

To conserve water, choose native and low-water-useplants whenever possible. Understanding theparticular needs of your plants is also crucial. Soilconditions, sunlight requirements, water and spatialneeds (i.e., the sizes and shape of root zones andbranching habits) will all affect the long-termsuccess of your roof-reliant landscape.

Xeriscaping uses the concept of plant “zoning” orgrouping. By grouping plants with similar waterneeds together in specific “zones,” the landscape canuse water more efficiently. Low-water-use plantsshould be grouped together, away from the high-water-use plants. (See page 41 for a completedescription of plant zoning.) Also, take advantage ofwarm or cool “microclimates” (the small areas ofdifferent climatic conditions around a property thattypically occur near walls, shade trees, etc.).

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Roof-Reliant Landscaping Chapter 1: The Fundamentals of Waterwise Landscaping

Appropriate Turf Areas

Low-Water-Use Plants

Using microclimates as places to group plants withsimilar needs is a great way to create areas of interestand diversity in the landscape. (See Figure 1-1.)

Figure 1-1: Microclimates are small areas in a landscape thattypically occur near walls, underneath shade trees or byanother landscape feature.

From a plant-choice standpoint, other kinds ofuseful information come into play, too. Is aparticular tree species a shade tree or anornamental tree? Does a species of floweringperennial bloom in spring, summer or fall? Will thisshrub grow tall enough and densely enough toblock the wind when you are sitting at a table onyour patio? Will this flower’s fragrance make yousmile or sneeze?

A roof-reliant landscaper must also consider theseadditional plant characteristics: (1) whether aspecies can be established in three to five years, (2) whether a species will typically, once established,bounce back from drought and (3) whether aparticular species can survive with precipitationwater only. The Office of the State Engineer isdeveloping a statewide xeric plant list, WaterwisePlants of New Mexico, that will be helpful in thisregard. Email waternm@state.nm.us or visithttp://www.ose.state.nm.us (click on Water Useand Conservation).

5. Efficient Irrigation. It doesn’t make sense todesign a roof-reliant landscape that uses waterinefficiently. A well-planned and well-maintainedirrigation system significantly reduces a landscape'swater use, which is especially important whenrelying on rainwater harvesting for most or all of itsirrigation water. For the most efficient use of water,irrigation zones should be designed so that low-water-use plants receive only the water theyrequire. Low-volume drip emitters are the mosteffective mechanism to deliver water to the rootzones of most trees, shrubs and perennials. Chapter10 covers the distribution of water to the landscapein detail, including drip irrigation, the most efficientwatering method.

6. Mulch. After building healthy soil by addingcompost and planting water-thrifty plants in theappropriate locations, you will want to furtherconserve water and promote plant health byspreading a thick layer of mulch over yourimproved soil. Mulch does five critical things forsoil: it shades, insulates, prevents erosion, adds

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Roof-Reliant Landscaping Chapter 1: The Fundamentals of Waterwise Landscaping

Efficient Irrigation

Mulch

nutrients (especially if fibrous mulch such asshredded bark is used) and obstructs weed growth.

Shading the soil with mulch prevents water loss dueto evaporation and also provides habitat forimportant microorganisms.

Insulating the soil from ambient air temperaturesprevents plant stress caused by the rapidtemperature changes that can occur in the highdeserts of New Mexico. Soils and plant roots do notrespond well to intense heat or cold, so having ablanket of insulation in the form of a thick layer ofmulch keeps soil at a more constant temperature.This is equally important in winter and summer.

From a soil-erosion standpoint, mulch can helpprevent wind from blowing the soil away. Mulchcan also help prevent erosion caused by majorstorm events. Even though its effects are usually lessvisible than those from storm-water-inducederosion, wind-induced erosion can have a largernegative impact on our fragile soils because of thefrequent (sometimes daily!) blowing thatunprotected, exposed soil receives.

Simply by creating a microclimate suitable formicroorganisms, even inert mulches such as gravelwill help to increase the nutrient level in soil. Whileorganic mulches (such as bark, straw and pecan shells)will provide more nutrients than inert mulches, theytend to need replenishing on an annual or biannualbasis. By contrast, inert mulches can sometimes lastyears before needing to be replenished.

Typically, the thicker the mulch, the more effectiveit will be as a weed barrier. Smaller and lowspreading plants may be mulched two inches deepuntil they grow larger, while larger trees and openareas (including pathways) should have a minimummulch depth of four inches.

If perennial weeds are a problem, a water-permeablecommercial-grade weed barrier, such as landscapefabric, can be placed underneath any type of mulch.(Remember, do not use nonpermeable plastic as aweed barrier.) Weeds that grow out of any mulchcan sometimes be difficult to control, but weeds thatgrow out of gravel mulches can be extremely

difficult to extract. Rock and gravel mulches shouldbe weeded often, before weeds can establish largeroot systems.

Gravel and stone mulches have many benefits, butthey can reflect light in a manner that is often toobright, and these mulches can create “heat islands”if overused. Breaking up stone-mulched areas withone or two organic mulches can improve theaesthetics of your roof-reliant landscape. The mostinteresting and perhaps most important waterwiseaspect of stone mulch is that it can create moisture;condensation collects underneath the rocks whenthere is a change in ambient air temperature in ashort period of time.

The smallest form of stone mulch is called crusherfines, which are extremely small pieces ofcommercially available gravel. They are often notmuch bigger than grains of sand and are typicallyrolled or tamped into place. They provide a clean,relatively natural look since their color often resemblesthe ochre tones that we recognize in our native soils.

Other common mulch materials include bark, woodchips and pecan shells. A less commonly used mulch,straw, is one of the more effective mulches forretaining moisture and providing nutrients for yoursoil. Contrary to popular belief, straw will almostnever blow away if properly laid, and the aestheticsof straw are quite natural because the sun quicklybleaches out the bright yellow hue of a newlyopened straw bale.

Bark mulch and pecan shells help soil retainmoisture, and they add nutrients to the soil as theydecompose. Compared to gravel, these mulches arelightweight and easy to install. However, in areaswith strong winds these lighter-weight materialswill be the most likely to blow away.

The types of plants selected for the landscape canhelp you determine what kinds of mulch to use.Less heat-tolerant, more moisture-loving plantsprefer fibrous mulches, while xeric (sun- and heat-loving plants) prefer gravel and stone mulches. Forexample, many desert wildflowers grow much morevigorously and live longer when mulched withcrusher fines or small pebbles.

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Roof-Reliant Landscaping Chapter 1: The Fundamentals of Waterwise Landscaping

7. Proper Maintenance. Although xeriscapes anddryland gardens are low maintenance, they are notno maintenance. Keeping your roof-reliantlandscape healthy through a well-timed program ofpruning, fertilizing, weeding and pest control willensure that your landscape develops beautifully andkeeps growing for many years to come.

The Importance of Erosion Control

If you go through the steps of creating a roof-reliant landscape using the seven basic xeriscapingprinciples highlighted above, it is important to takethe necessary precautions to prevent your precioussoil from eroding away during heavy storm events.Grade your garden in such a way that moisture canpercolate into the soil, preventing the soil frommigrating downhill.

Unless your property is completely level (and veryfew properties maintain a consistent elevation fromone end to the other), you will want to grade yourplanting areas so the velocity of the storm waterthat flows during a high storm event is significantlyreduced. One way to do this is to form “plantpockets,” as opposed to “tree wells,” around yourplants. As shown in Figure 1-2, tree wells arecompletely circular, while the plant pockets, or“mini-swales,” are designed to accept storm water.

The small berm making up the pocket is placed onthe downhill side of the plant or tree such that nopart of the berm blocks nearby storm water runoff.Conventional tree wells divert this runoff awayfrom plants while simultaneously increasing thevelocity and mass of the storm water, which canquickly create serious erosion problems. Properlyplaced plant pockets slow the water down,minimize erosion and allow time for infiltration totake place at the plant's root zone.

Ideally, plant pockets should be situated in a fish-scale pattern (depicted in Figure 1-2 below) so thatnone of the soil near your plants erodes duringlarge storm events. Consider using the spoils fromyour native soil excavation for building your plantpockets. Just be sure not to allow moisture to backup against any structures.

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Roof-Reliant Landscaping Chapter 1: The Fundamentals of Waterwise Landscaping

Figure 1-2: Mini-swales or plant pockets (left) are designed to hold some storm water near plants. Tree wells (right) completelycircle the root area and can be filled with irrigation water.

Proper Maintenance

If your property is steep enough and your financesallow, you can also build retaining walls to holdback some of the soil that you excavated to makeroom for compost and mulch. The resulting terraceswill control erosion and serve as more highlyengineered planting pockets. If terraces do not fitwithin your budget but your erosion potential issignificant, on-contour earthen swales and strawbale swales can be used in some cases.

An on-contour earthen swale is a ditch dug alongpoints on a slope that are all at the same elevationabove sea level. Points on the same contour line canbe determined by using one of a number of simpledevices, including laser levels, tripod levels, waterlevels or A-frame levels. The dirt from your ditch isthen placed on the downhill side of the ditch in theform of an on-contour berm. On either end of theirberms, swales turn upslope in order to control therunoff that causes erosion.

In the event that your site is too steep for earthenswales, you can install straw bales and otherpermeable barriers that can reduce soil erosion on aslope. As you establish plant material next to thesebarriers, the root systems of your plants strengthenthe soil in the vicinity of the barriers. Over time, allof these barriers disappear, leaving healthy plantsand soil behind.

NOTE: The above information about xeriscaping isnot intended to be a comprehensive resource. Formore about dryland gardening and the traditionsof land use in desert environments, see Appendix 8.

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Roof-Reliant Landscaping Chapter 1: The Fundamentals of Waterwise Landscaping

Figure 1-4: Workers install a straw bale swale.

Figure 1-3: Retaining walls are an effective way to createterraces to control erosion and create spaces for plants.