Choosing plants for a Phoenix yard
How to choose plants for a Phoenix yard from the four things the climate asks of them, with a comparison of the plant categories the local lists are built from.
Short answer
A plant suited to a Phoenix yard has to survive two things at once (a summer with 111 days at or above 100 °F, and a handful of winter nights cold enough to matter). Choose by the spot first, then by water need, size and whether the plant is safe around pets.
A Phoenix yard is a set of conditions before it is a set of plants. The sun lands hard, the soil is alkaline and often caliche underneath, the rain is about seven inches a year, and the two stretches that kill plants are not the ones people expect: a summer that runs five months, and a winter that is harmless most years and not every year. Choose a plant that suits the conditions already there and the yard mostly looks after itself. Choose against them and you spend the summer watering a plant that was never going to be happy.
The chart below is what “conditions” means here, counted: how many days the year spends above 100 °F and how many nights it spends below 40 °F.
The two limits a plant has to survive
Normal days at or above 100 °F, and normal nights at or below 40 °F, by month at Phoenix Sky Harbor. Heat is a six-month problem; cold is a small one concentrated in December and January.
Normal day and night counts by month, NOAA NCEI U.S. Climate Normals 1991–2020, Phoenix Sky Harbor (USW00023183). Summed across the twelve months, the heat series comes to 111.3 days and the chill series to 14.0 nights below 40 °F, with 0.6 of a night a year below 32 °F. The heat is the design constraint; the cold is the detail most plant lists are written around.
The four questions, in order
Every plant list for this climate, however long, is a set of answers to the same four questions. Ask them of a plant in this order and the choice mostly makes itself.
How much sun, and when? Full sun in Phoenix means something harsher than full sun in a temperate place, because it comes with 100 °F air and ground that runs hotter still. The question that matters is not simply “full sun” but “which hours”, and in particular whether the spot takes the western sun. A plant that tolerates six hours of morning sun can be cooked by four hours of afternoon sun against a west wall. The Sun Path & Shade Finder works out which walls take the afternoon sun on a given date.
How much water? This is the question the plant lists answer most precisely, and the one worth getting right, because water is the running cost of the yard. The Hydrozone Yard Planner exists to group plants by water need so that one irrigation line is not being asked to serve two different answers.
How big, ultimately? A mesquite planted three feet from a wall is a problem in ten years that cannot be solved in ten minutes. Mature size, not nursery-pot size, is what the spacing has to be set to.
Is it safe around the household? Pet toxicity is a property of the species rather than of the category, and the only list this site will cite for a named plant is the ASPCA’s own toxic and non-toxic plant list. The dedicated guide is plants that are safe around pets.
The categories, compared
The local plant lists are built from a small number of categories, and each category has a different job and a different set of tolerances. The table below is this site’s summary of them. The ratings are groupings rather than measurements: a named species can differ from its category in any column, which is precisely what the Desert Plant Picker is for.
| Category | Job in the yard | Sun | Water once established | Frost risk | Notes |
|---|---|---|---|---|---|
| Native desert trees | Shade, structure, screening | Full | Low | Low | Deciduous, so shade is seasonal; some shed pods and litter |
| Desert shrubs | Screening, seasonal flower | Full | Low | Low | The backbone of a low-water planting; most flower in spring |
| Cacti and succulents | Form and accent | Full to part shade | Very low | Varies by species | Some are frost-tender despite the heat tolerance |
| Desert perennials and grasses | Colour and movement | Sun to part shade | Low to medium | Varies | Often short-lived; expect to replant |
| Shade trees from wetter climates | Fast, dense shade | Full | High | Varies | The highest water demand in the yard, by a wide margin |
| Turf | Recreation surface | Full | High | Low | A water decision rather than a plant decision |
Two things are worth saying about the shape of that table. The first is that the low-water end of it is the largest, which is not an accident of the climate but the point of it: the plants that belong here are the ones that were already adapted to a place with seven inches of rain. The second is that the high-water end is not forbidden, it is expensive: a yard can have a lawn and a shade tree, and it will use several times the water of one planted from the top of the list.
A worked example, and the rule behind it
Take a south-facing front wall with a bare strip four feet deep in front of it. That strip gets the worst of the sun in the middle of the day and reflected heat off the wall in the afternoon, which rules out the two moisture-loving categories immediately and makes the third one risky. The honest answer is a desert shrub with a high heat tolerance, or a cactus or succulent, spaced to its mature width and not to its nursery-pot width.
Now take the same strip on the east side of the same house. It gets morning sun and afternoon shade, which is a different climate entirely: mild enough for a desert perennial, and mild enough for a plant that would not survive the south wall. Same house, same soil, same water, opposite answer. This is the whole of the method: the site decides, and the plant list is what you consult afterwards.
The other half of it is grouping. Once the sun is understood, plants on the same irrigation line should want the same amount of water, which is the idea behind hydrozoning a desert yard. And if the aim is shade rather than flowers, the native trees worth planting for shade is the list to start from: the fast-growing options are usually the thirsty ones.
What the label will not tell you
Two phrases on a nursery label do more damage in this climate than any other.
The first is “drought tolerant”. It is a true description of the plant and a misleading description of the first year. Almost nothing is drought tolerant while it is establishing, because the roots that make it so have not grown yet, and a desert plant that goes into the ground in June and is treated as though it were established will not see autumn. The establishment year is the one time a desert plant needs help rather than neglect.
The second is the mature size, which is printed on the label as the size the plant is expected to reach rather than the size it will reach in a yard with irrigation. In a watered garden, many desert plants grow faster and larger than the number on the tag. Spacing to the printed figure and figuring the plant will stay there is how a hedge becomes a wall.
The other thing the label leaves off is the soil, which is the one condition you cannot choose for. Valley soil is alkaline, and much of it sits on caliche, a hard, lime-cemented layer that stops water and roots alike. A plant that wants a deep, well-drained root run will not find one above it, and the fix is to plant into a well-prepared pocket rather than to water harder.
- NOAA National Centers for Environmental Information: U.S. Climate Normals 1991–2020, monthly summaries, Phoenix Sky Harbor (USW00023183)
The normal days at or above 100 °F and the normal nights at or below 40 °F by month, which are the two series in the chart.
- NOAA National Centers for Environmental Information: U.S. Climate Normals 1991–2020, annual and seasonal summaries, Phoenix Sky Harbor (USW00023183)
The annual figures (111.3 days a year at or above 100 °F, and 0.6 nights a year at or below 32 °F).
- University of Arizona Cooperative Extension
The plant categories used for low-desert landscapes, and the guidance to select for the site rather than for the plant.
- American Society for the Prevention of Cruelty to Animals: Toxic and Non-Toxic Plant List
Which plants are listed as toxic to dogs, cats or horses, which is the only pet-safety list this site will cite for a named species.