Drought tolerance is an interesting topic. I’ve written on it before, but now have some additional thoughts to add, in part because we have recently moved to much more arid Central Oregon. A drought tolerant plant in Portland is a very different thing than one here where annual precipitation can vary from around 13″, very rare, down to as little as 5″, commonly 8″. While Oregon in general is considered to be a mediterranean type climate with dry summers and wetter winters, Redmond’s climate is strongly influenced by drier continental patterns. This last January, ’23, we received only 1/4″ of precipitation while Portland had 7.32″ about 120 miles to our northwest, on the ‘wet’ side of the Cascades. Drought tolerant then means different things in different regions and can vary widely within a region along with soil conditions, slope and aspect (which direction a site is oriented). Generally speaking, drought tolerance refers to the ability of a particular plant to endure periods in which available soil moisture is below that needed to support the plant’s metabolism. A tolerant plant can ‘bridge’ these naturally occurring ‘dry’ periods. An intolerant plant will suffer cellular, even structural damage and may be unable to flower and produce seed. Health is compromised should the drought last too long, resulting in internal physical damage and leaving it more subject to infection or infestation. A drought tolerant plant will have the capacity to respond in a healthy manner when soil moisture levels return to those that support active growth. Within these limits the stress it accrues does not compromise its health…beyond it though….Damage is accumulative. String a series of drought periods together and a plant’s capacity to recover is compromised. Because patterns of precipitation, of water storage and movement, vary widely across the earth, regions and sites have different plant communities associated with them. The condition of drought stress then varies with the location and the species. A drought tolerant plant on one site may crisp on another drier one. Of course this can work in the opposite sense as well, that a site may be too wet, but that’s another story. In the case of the PNW and many other regions, it is also the timing of the precipitation, when it occurs during a plant’s cycle of growth and dormancy.

Native plants, on undisturbed sites, which have selected their places are, as a rule, drought tolerant…there! What most gardeners want to know is whether a plant will be drought tolerant for them! Where they’ve planted it! Any plant’s limits and requirements are determined by their genetics and the places in which they evolved and adapted. All plants have the capacity to adjust to varying levels of available soil water though for each they may be different. A plant whose natural range can be defined as a ‘mesic’ forest won’t have much chance of survival under arid steppe or desert conditions. They literally don’t have the ability in them. Native plants, on undisturbed sites, functioning within the seasons and the wet/dry cycles they were ‘selected’ by, are largely ‘tolerant’. Go beyond them though, whatever they are, and any plant can be under stress. Each has its particular limits. Each individual will vary in its adaptability/tolerance. A drought tolerant juvenile plant has lower limits, it has softer often thinner tissues and smaller reserves to rely on and a more limited root system to support them. Even the most ‘adapted’ plant may desiccate long before they reach maturity, if the conditions stress them too much. Young plants often can’t tolerate the conditions they are seeded into. Tolerance can thus vary significantly from individual to individual of the same species and over the course of its life.

Individuals may germinate, but then fail to compete with their neighbors for a limited water source. Individuals are a part of a community and many, if not most, seedlings don’t survive the competition, in the wild, presented by other members growing nearby. Any individual exists within the limits set by its place and community. While competing for survival it must do so within these limits. They tend to sustain a healthy community, whether that means they mature, flower and reproduce or give up their space for another individual of the same or different species.  Resources are shared and limits are set outside of the individual. In this sense community members must ‘cooperate’ and individuals will necessarily be sacrificed. Individuals are role players. While particular species or even individuals many dominate, that is for a limited time period. Other community members, other species, are also necessary and space must be afforded to them.

[The relationship between individual community members is not always just competitive. It has been found, for instance, that more deeply rooted plants in forest, savanna and prairie communities, can bring water up from deeper levels and make it more available to those shallower rooted members. It is also true that in some intact communities individuals of the same species, various NW conifer species, especially those descendant from local ‘mother’ plants, may root graft, or connect via mycorrhiza, and ‘share’ water and nutrients, essentially ‘nursing’ younger and or stressed plants to assure their survival and the ‘community’s’ continuation. This has been studied in the PNW by forest ecologists. See Suzanne Simard’s work.]

Like so many things in nature this is a matter of pattern and probability. Communities will contain a variety of species that tend to combine in relatively stable patterns, each member filling a niche or role until through disruption, the maturation of individuals, or through the wider process of succession, the ‘maturation’ of the community, a different species comes to dominate, and a new pattern takes hold…or the cycle simply begins anew, never exactly the same. Natural communities are dynamic, following patterns, but not rigidly so. Those individuals of a species which survive are among those best sited or suited and are positioned to reproduce and pass on their genes and traits. Their progeny are not assured the role of survivor. While communities possess stability there is considerable variability over time, in their numbers and the mix of community members. The cycle itself continues.

Larger perturbations can radically alter this, but these are by definition rare, widely scattered events. Asteroid collisions, the glacial phase of an ice age, a cycle of volcanic activity, a ‘wildfire’, a landslide, these can cause a radical reset. Those dying, leave space for other members of the wider community. But overall a balance is maintained. The patterns are dynamic, often cyclic with definable limits. Drought tolerance is simply a trait all plants have, one we only recognize as such, when water availability becomes ‘marginal’ and begins to push a plant to its limits.

All plants have the capacity to draw water from their environments, they must, so we are talking about extremes here. Drought tolerance then is our recognition of a plant’s capacity to do this and to survive on ‘less’ than we might expect. It goes to the plant’s ‘durability’ and toughness under harsh conditions. Doing this ‘well’ confers a survival advantage to a plant. Within its biotic community such a plant is more capable of accessing a vital and limited resource whether that is the result of a deeper weather cycle, a water limitation that results from other plants removing the water or human caused climate change or our messing with its supply. Drought tolerance speaks to a plant’s vigor and its capacity to remain healthy. Should that locality became wetter as a result of a disturbance or change, that drought tolerance may become a disadvantage. It may, in such a case, be too good at drawing in water. Drought tolerance is only one of many individual traits that play a role in the composition and health of the larger system/community. Members are ‘selected’. Other traits are every bit as vital.

Plants and their communities are conservative, they do not risk their futures on one strict pattern or limited characteristic. For every plant to survive, is an impossibility. Decline, death and rot are essential in a healthy community, it is necessary to provide the space needed for an individual, to recycle nutrients which would otherwise be quickly exhausted and in providing for the conditions shade to soil health a plant might require.  What if a species were immune to drought stress. What if they could switch their metabolisms on and off and ‘harvest’ all of the water on a site…then the individuals of other species of the community would fail, leaving the one supremely adapted to drought alone. Diversity and complexity are strengths in a biotic community. They attribute a degree of resilience to a local community. Having one species, making it a one note monoculture, dominating all others, sets up a situation, that were it to fail because of a change it was susceptible to, the entire community would fail. Being drought susceptible is in this sense a necessary trait for the survival of the larger biotic community.

Life has never been about the individual. Thinking it is, is a human weakness, a harmful bias. Today, when we create gardens and landscapes, we are skimming off select members of communities, putting them together for our own purposes and then expecting that they remain healthy, stable members in our schemes. This isn’t necessarily realistic and more experienced gardeners understand this which is why they are observers and become students of plants and their communities. There must be limits on how long any plant can survive ‘dry’, just as there are limits to their tolerance for cold, heat, soil chemistry, etc. etc. Plants die in order to sustain the community. The community would quickly become overwhelmed without this continuous culling of individuals. If not, all would be lost. Drought stress and failure are part of a necessary complex of controls that limit and shape living communities. All things must die. It is a part of any local community’s ‘dance’.

Under natural conditions plants begin and establish on given sites. Those conditions exist within a particular range…necessarily. Too much variability and the more ‘marginal’ members, important role players, will be lost. Conditions must follow particular patterns. Stable conditions allow stable communities. Significant disruptions to those conditions can result in radical restructuring of biotic communities and the loss of some species. Surviving indicates that a plant is adapted to conditions there…that it is not just ‘drought tolerant’, but tolerant to some degree to the range of all of the conditions extant on a site. As any single site condition changes, be that of the climate, the addition of competitive invasive plants, the interruption of surface or ground water flow, soil compaction or contamination, even the maturation of the many other plants and organisms living there, any given plant may be put under stress. Individual plants are drought tolerant, adapted to the conditions and the hydrology of their particular sites, but they are not immune to more severe cycles of change. Health and vigor are a result of the entire ‘suite’ of conditions offered on a site. Degrade or change the conditions and any plant may be pushed past its limit…and conditions are always in a state of flux.

Each individual goes through its life, growing through juvenility, into maturity, reproduces, declines and dies, unless interrupted by death, exhibiting a degree of vigor that matches its stage of growth. Each has a particular life expectancy, which may be compromised and shortened when put under repeated or extended periods of stress. This is no different for us as individual human beings. If we cannot remain sufficiently hydrated, we will suffer. If this goes on for extended periods we will begin to incur cell, tissue and eventually organ damage. Our tolerance as humans to ‘drought’ is quite low. We require water every day. Our bodies themselves do not ‘store’ any. It is all in active use. All living organisms will meet a similar fate when ‘drought’ stressed. Under stress all organisms will become more subject to disease and infestation. Their internal systems will be slowed and compromised. Whatever energy stores they have will be shrunken. Should it happen to us we can expect that our lives be significantly shortened.

Water is essential for virtually every cellular function in every organism. Our being humans and mammals, with relatively high metabolism rates, means that we are subject to catastrophic failures as our hydration level drops outside a very limited range. Many plants have adaptations which expand their range in part allowed by their slower metabolism rates and the fact that they are anchored in place, unable to move toward water. Plop us down in the middle of the Sonoran Desert without a water supply and we will be in serious trouble by the end of the day. We cannot shut down, go dormant, shed ‘leaves’ or draw water from less important cells, sacrificing them, to sustain core functions. Many plants can. The limit to our own tolerance to dehydration is quite low. Plant species have evolved many adaptations which increase their tolerance to drought. Such plants have the capacity to withstand drought are able to remain in a ‘recoverable’ state. Think of a Cactus growing in the Atacama Desert in Chile, the driest place in the world, the Boojum Tree in Baja or the Ocotillo in the Sonoran Desert and those many California natives that routinely go summer deciduous to conserve water. Humans do not have a similar range of adaptations. We are a single species. To expect us to thrive under all of the conditions that the hundred’s of thousands of different species of plants do is plain silly…so we shouldn’t expect that of them…that too would be silly.

Today we use drought tolerance as a comparative term. We often forget that drought tolerance is extremely variable and will be different for every plant on every site. This is complicated today because we have available to us many thousands of plants from the earth’s far corners, corners that have wildly varying conditions and, when we bring them home to our gardens, too often combining them in crazy melanges whether they are appropriate for our own ecoregion or not, we often expect them to do well in spite of the variability. Will this grow here? Is it cold hardy? Is it drought tolerant? Are the light conditions and climate fitting? If we filter all of the possibilities available to us, by whether they are cold hardy here and make another list of those plants which are drought tolerant on our site, we will have two different lists, with some overlap. If we want to make a coherent garden, we will look at all of a plant’s traits. The closer our plant choices cleve to the conditions we can give them, the less ‘work’ we will have simply to keep them alive, and, I suggest, that they will share a visual coherence. Plants selected for shared conditions tend to look like they belong together.

Conditions go toward shaping morphology. This is why vastly different genera from sites isolated from one another, even from distant continents, may share a similar appearance when they are shaped by similar growing conditions. Genetically, they may be very different, but morphologically similar. Consider the Cacti of the western hemisphere and the very similar appearing succulent Euphorbia of Africa. They are very easy to confuse for the novice. Such Euphorbia are often commonly called ‘cactus’ even though they aren’t. Study any undisturbed native landscape, their plants are adapted to their site conditions. When someone asks, is this plant drought tolerant, the answer will be meaningless without an understanding of what is normal for the plant and exactly what the conditions are on the site being discussed. There is no such thing as a particular class of plants that are drought tolerant and so can be planted with impunity wherever the gardener might like. Locally drought tolerant plants can still die. Water is not the only factor in a plant’s success or failure.

Drought Adaptation

Like any other organism a particular plant species may be more broadly adaptable than most others. Such generalists are favored by nursery producers and retailers because they can be marketed more broadly. They will have a higher rate of success in wider ranging gardens. It doesn’t make them ‘better’. The best plant, if there is indeed such a thing, may be very limited in terms of its site conditions, but one must look for these because they aren’t going to be so readily available…and they will require that the gardener be better informed to buy and successfully grow such relative rarities. Gardening success is much less dependent on a gardener’s skill set than it is on knowledge and the observational skills needed to understand what matters for a plant. Given the right conditions a plant will grow on its own. We don’t so much grow plants as we ‘allow’ them to perform.

There is not a quality or single trait that, when assessed, drought tolerance can be attributed to. There are a suite of traits, not all of which must be present to effectively increase its tolerance. These can include their root systems which may penetrate to depths where water is more available or, counterintuitively, thoroughly penetrate the surface so that they are able to take advantage of even light rains.

Other physical characteristics such as a plant’s form, the shape and character of its leaves, how they are ‘held’ and their attachment are a factor. A plant’s structure may work to shed precipitation away from its crown where common conditions might cause it to rot. Another, such as the species of the rosette structured genus Agave, utilize their leaves to concentrate precipitation near their crowns a helpful adaptation for a desert plant dependent upon sporadic monsoonal rains. Planted under wetter conditions an Agave’s structure cause them to rot. Such is the case when growing them west of the Cascades, especially given that there, rain falls most heavily in winter, when Agave aren’t growing due to temperatures which are too cool. 

Drought tolerance most definitely involves a plant’s photosynthetic process, of which, there are three types, identified as C3, C4 and CAM, each one progressively more efficient in terms of internal water use. Different species may rely on a single type or a blend, made easier by the fact that the basic chemical process is the same, but the ‘pathways’ to get there vary. Some plants utilize different pathways at different stages of growth, being most inefficient, wasteful, and dependent upon water access in their juvenile forms when many utilize C3. (Look up photosynthetic pathways. I have briefly reviewed these in earlier posts.)

Other morphological attributes, the physical structure and appearance of their individual leaves and attachments to their stems, go to reducing a plant’s water losses. One entire group of such plants are often defined as sclerophytic, plants whose generally thicker leaves have evolved with shared characteristics that reduce their exposed surface areas, toughen them, often shortening their petioles and the internodes separating them, creating a more compact, less exposed, plant. Sclerophytic plants ‘protect’ their leaf surface, their epidermis, from desiccating forces such as heat, low humidity and wind. Water loss out stomata is a normal cost of the photosynthetic process. Those best ‘geared’ to surviving droughty conditions have gradually come to dominate many arid landscapes. The more severe the pattern of drought the more extreme the physical adaptations may become. Such plants will tend to have smaller, ‘harder’ leaves, fewer stomate or, they may dispense with leaves all together and rely on conducting photosynthesis via the chlorophyll held in the chloroplasts within tougher bracts and the harder structures of their stems. (Think of plants like the Ephedera spp.) The leaves themselves may be more rigid and thus tolerant of lower water concentrations within. Their surfaces color may shade to blue, gray or white, reflecting away heat producing cooler internal conditions and thereby resulting in less water loss. They may curl or roll in on themselves effectively lowering their surface area exposed to desiccating conditions. They may develop trichome structures extending above their more vulnerable epidermis, tiny hair like structures that may collectively shield it from exposure or, in the case of those drought tolerant members of the Bromeliad family, encase their strappy leaves in a hard protective ‘shell’ of tiny, connecting ‘plates’.

Others still, often those which occupy dry tropical, subtropical on into warm temperate climates, pursue the strategy of drought deciduousness, shedding leaves during the periodic low water cycles they experience and growing them back with the arrival of sufficient rains. Chaparral plants are often sclerophytic and their leaves, being evergreen and persistent, saves them the energy and water necessary to replace them annually or seasonally. Some are very adept at this. The Bristlecone Pines, like Pinus aristata and P. longeava, framing the West’s massive Great Basin region, may retain their needles, hardened leaves, for 14 or more years before shedding them.

Other plants, notably those we collectively term ‘succulents’ are able to store water in their tissues that can later sustain them over long drought periods, periods that are to some degree necessary. When succulents grow in wetter conditions than those they evolved with their saturated tissues can begin to rot. Many other drought tolerant species are subject to fungal foliar diseases their leaves unable to resist certain fungal infections when the stressed ‘wet’ plants can be infected. Alternatively plants, native to areas where drought is unheard of during their growing season, can be expected to have few of these drought surviving capacities, although if freezing weather is a cyclic occurrence, such plants may have developed some of these same capacities, plants growing in such cold to frigid climates face a cold induced ‘drought’ as water, previously available, is frozen into solid, crystalline form. Plants rarely invest in single purpose strategies. To do so is an extravagance that may leave a plant potentially vulnerable during marginal conditions.

As aridity increases local species tend toward more ‘thrifty’ forms and sizes. Trees tend to be smaller before being eliminated altogether. Shrubs do much the same. The plant communities themselves respond to this becoming less ‘layered’ and dense as available water becomes less available.

Another group of tolerant plants are those herbaceous perennials and annuals able to speed through their cycles, like those adapted to the mediterranean conditions of our Pacific Coast with our cool wet winters and warm dry summers. These plants often ‘rush’ through flowering and seed production before summer bakes the soil dry, the tops dying down, thus protecting the crown, their meristem and whatever in ground storage organs they may possess to power their next burst of spring growth.

Many of the world’s bulbs are adapted to summer dry mediterranean conditions packing their active phases into the wetter, cooler, shoulder and winter seasons as cold permits, completing their active growth before going into summer dormancy.

Establishment and the Importance of Place

Drought tolerance is also dependent upon whether the individual plant is established adequately on its site. A poorly rooted plant cannot reach the water that may be available to it in the soil. While water does move through soil due to physical forces which exist between water and soil, it will not simply bridge the dry gap between itself and and roots. Growing roots, ‘sensing’ the presence of water will grow toward it if possible, but to do this requires some minimal concentration of water in the soil to support its growth. Dry soil, that which contains no available water, cannot sustain growth and a plant’s tissues will begin to dry as its cells, supported by appropriate heat and light conditions, will continue to attempt to transpire, conduct water through its tissues and exhaust it into the atmosphere through its stomata. Drought tolerant plants may die after planting out nearly as easily as those which aren’t, if they are too stressed before they can get their roots out into the surrounding soil to access the available soil water. Establishment is very dependent upon the condition of the plant going into the ground and how we care for it during its establishment period. If it is already stressed going in, its ability to root out is going to be compromised. Additionally, if we only keep the root ball moist while the surrounding soil dries after planting out, the roots will never reach out and establish the plant. This is one of the problems in the arid West where the summer growing season isn’t supportive and growth ceases…especially so when we are attempting to grow plants from regions which experience a pattern of summer rains and they can’t. Such plants additionally will spend their energy stores quickly and be unable to replenish them.

Plants commonly identified as regionally drought tolerant are then inevitably only a very small segment of the possibilities. Choosing plant material will always require more detailed and intimate knowledge of the plant in question and of the specific site. To ignore this and focus only on the so called, and commonly promoted, ‘bulletproof’ plants available in the market today, unnecessarily narrows the pallet of plants that tend to survive across a variable range of conditions common to a region.

 

 

 

 

 

 

Thermodynamics and the Energy of Life

We often treat our landscapes and gardens as our ‘own’ limited by our own desires and pocketbooks. The needs of nature and place are too often largely ignored. Residents today are often indifferent. One’s yard may serve as little more than a defensive perimeter, a location for active children and/or pets and a claim on status. Nature has never worked this way. In nature, we, all organisms and things, belong to place.

It would be better to think of landscapes as dynamic, energetic organic systems, ‘working’ to reach a ‘balance’ however far off that may be. Energy, in the form of sunlight. Organic systems, living organisms, have been driven/shaped by the energy of sunlight for several billion years. Plants, all organisms, conduct energy and are shaped by the flow itself. Matter can be thought of as precisely ‘structured’ forms of energy (E=mc², energy equals mass times the speed of light squared…remember). It’s strutcture, its organization, contains energy. Energy, in its proper form delivered in the proper amount, animates/organizes masses into precise forms and systems, which in turn regulate the flow. Thermodynamics, the study of the flow of energy through mass, has shown over the last 50 years, that organisms are in a highly organized state and, as such, are out of ‘balance’, ‘falling’ continuously toward entropy, a state of disarray, randomness, and death, but for the energy which continuously drives them, until such a time that those structures can no longer maintain themselves and their operation. This is a huge topic in itself I have written of previously. Search under ‘thermodynamics’.

The balance of such a ‘healthy’ organic and living system is a product of this complex flow, each member of the community fulfilling its role, determined and powered by it. As long as conditions continue within limits, the community, like the organism, will continue in It’s dynamic, living, within parameters we would recognize as healthy, changing constantly within that limited range, repairing and replacing its ‘parts’, shifting gradually from one set of conditions to another. (These changes are minimal in the wet equatorial tropics, lacking the seasonality of temperate and more extreme climates,  and so are the most stable. These natural systems can be severely compromised by our unconsidered actions. Add to this a gardener’s tendency to impose our own vision on the landscape, and we may be operating far outside of the natural limits of a place. Too often we begin doing things simply because we can. Watering, has become such a thing. It has  become a ‘normal’ part of gardening, one we hardly question, at least in the arid West (How, we may ask ourselves, can we garden here if we don’t water?) and drought tolerance has become a question of how much to water.

Irrigation, its Effects and Practice

Normal, across much of the arid West, is to have a landscape which quickly turns to a more monochromatic palette of tan, sere, buffs, the bleached ‘bones’ of dead branches and the silver’s and grays of foliage disguised and protected from the summer sun’s intensity, the extremes of aridity and cold. For many, this drives them to add a liberal ‘infusion’ of green to their home gardens and landscapes. This means water. This means ‘living’ beyond the means of one’s place. Tapping water reserves and, in so doing, compromising the future and taking what other species and systems need to survive.

Gardening then has become a cultural practice, removed, to some extent, from the limits and conditions of one’s place. Place and its conditions are to some extent, suspended. What then does drought tolerant mean in this context?

All of this goes to say that when catalogs, friends, plant labels affixed by growers and retailers, tell us that our plant choice is drought tolerant, we must be wary and understand that there is more to this than might first appear. It is not that people are all attempting to deceive us in an attempt to simply sell us a plant, though they might be, but the process of living is complex. As when we shop in general it pays to be ‘informed’, to understand what claims may mean. We in the west must contend with arid growing conditions, alien to us if we come from regions that receive significant rainfall during the summer growing season, and in opposition to the ‘greener’ dreams we have brought with us. We are largely unaware of the consequences of this decision and if we think about at all, discount them. If we consider them at all we may see them as someone else’s problem. If we and this place are to survive us, we must understand what it means to irrigate and what cost our increased water ‘share’ means for the future and other species, species not in a position to advocate and fight for their share. Our choices have a wider impact.

Water-Wise Plants and Summer Irrigation

When we read that a plant is purported to be ‘drought tolerant’, what does that mean? Communication is a difficult thing between humans even when we share the same language, the same meaning for words. Too often today ‘drought tolerant’ has been reduced to a marketing term. A plant either is or isn’t. But it is or isn’t what?…it will either live or die without regard to its care, without water? That is clearly an impossibility. What about during establishment?  If we must water it to establish it…when does it actually become tolerant? How do we know when we can stop watering? Requiring water for establishment confuses the issue. Plants are simple, right? We want their care to be simple. Consequently, it is far easier to plant those adaptable, bulletproof plants I mentioned above, and have the irrigation crew come by in the spring to ‘tune’ up our irrigation system, program it and never have to think about it again (They’ll turn it off when it needs to be). Plant our yards, turn on the system and be done with it! Now we enter into the world of ‘water wise’ plants and gardening!

Various localities have put together lists of ‘water wise’ plants for residents to reference when planning/planting their home gardens and landscapes. This phrase would seem to be even less firmly based in any kind of practical reality than would a list of drought tolerant plants. What exactly does it even mean? (Especially in the case of one local publication I’m familiar with for Central Oregon, a desert climate, which includes plants from parts of summer wet China and Japan.) It purports to address the issue of creating sustainable landscapes, but includes many plants that require supplemental irrigation here, not just for establishment, but for the lifetime of the plant, combined with locally drought tolerant natives. What??? Such a landscape admixture would require irrigation, to keep the thirsty maladapters alive while actually harming the drought tolerant natives included, which in the west are often intolerant of summer irrigation. A ‘water wise’ designation would seem to be a strategy to get around the general public’s ignorance of plants and place. Many natives of the arid West normally go dormant during the long dry summer period after quickly flowering and producing seed by early summer the soil water then generally exhausted. Yes there are a few exceptions like Big Sagebrush, Artemesia tridentata, with its several subspecies, and the Rabbitbrushes, actually two diffeent species, from two different genera, (We don’t make this easy for people!) which somehow muster the where-withal to flower late summer and early fall. Such consummately adapted local plants often die under conditions of warm and wet, which can promote an explosion of soil microbes which are fatal to said natives. Such native are unadapted to conditions created by regular summer irrigation.

Irrigation is a cultural practice used to grow plants that would not otherwise grow in a place or produce under local conditions. Irrigation has become normal in the arid West as residents continue to attempt to grow landscapes poorly adapted to local conditions. This may be justifiable for growing food plants, but when growing them strictly for aesthetic personal reasons, or to simply ‘keep up appearances!’ this should be understood as an irresponsible practice. It is interesting to me how so many people will only plant plants that will never freeze out under the most severe temperatures one can locally expect, but then plant things that look healthy only with a steady supply of supplemental water. We may bitch about its price, but many of us don’t even blink when pouring it on our yards to keep the postcard picture perfect. But that’s a different story.

The best strategy for the gardener, will always be to educate themselves about plants and to acquire some understanding of the operant conditions on one’s site. Pay attention to where plants originate and note how those conditions are similar or different from yours. ‘Experts’ really do a disservice to the public when they ‘fudge’ this confusing the message. What are we trying to do here?

At some point, if we pay attention we will begin to recognize how a plant’s physical features are often a key to the conditions it may prefer or even demand, giving us visual cues going to the plant’s adaptations. Plants offered in the nursery trade locally are likely not the plants best suited for our locale and garden. Look to the generally small, local, growers of natives and then to sellers/growers of plants in compatible regions. There are several hundred thousand species of plants and uncounted subspecies, distinct populations with their own traits and naturally occurring hybrids. Some will be far better suited for your garden/landscape than others.

You wont have to chose between all of these. The largest portion of plant species by far are native to tropical regions and you will never see them offered here. The further you are from the tropics and the equator, the more prone to winter cold and freezing, even arctic type events and the drier your local conditions will likely be. You will find that those plants tolerant, durable enough to take them, will be a relatively small group, okay they could include a few thousand, but a great many of those won’t be available to confuse you. Garden centers and big box stores are in business to sell product. Store buyers are themselves a conservative species, without backing, they cannot afford to stock each store with the best adapted plants across the country, even when they are available to them. Plants are a highly perishable product. Holding them indefinitely will cost them the additional dollars necessary to care for them, to up pot them and protect them over the seasons. Additionally plants are not manufactured. You can only make them from seed or the appropriate vegetative material…their production is limited and seasonal. Educate yourself and begin to request these plants. Some places will special order them for you. Availability will improve as demand increases. Seek out local growers of adapted plants (not just natives! There are many area ‘natives’ like Redtwig Dogwood, Cornus stolonifera and its several cultivars, that you will only ever find growing locally where they can get their roots down next to a stream or rare water body here in the desert. Native doesn’t mean it will work for you. In any event, as demand increases business owners will feel more confident buying ‘new’ material in to provide for their local customers. Support those growers willing to take the risk.