What actually grows here, and where you are

Your zone, and your neighbour's

The USDA updated the Plant Hardiness Zone Map in 2023, replacing the 2012 edition. Most of the populated parts of Washington County came out as Zone 8b. Not all of them.

The differences are small on paper and large in a planting bed. Santa Clara and La Verkin are a half zone colder than St. George despite being minutes away. Veyo, Springdale, Pine Valley and Central are not in the same climate at all. A bougainvillea conversation that makes sense in Bloomington is a waste of a customer's money in Pine Valley.

The wrinkle no plant tag carries

The Washington County Water Conservancy District publishes something in its Plant Zones brochure that is more useful than the map, and we have never seen a competitor quote it.

The District writes that the more densely populated parts of the county sit in hardiness zone 8, that a warm winter can behave like zone 9 while extremely rare years drop to zone 7, and that several zone 9 plants have grown in popularity but homeowners should understand they are taking a risk with them. Then the part that matters most: neighbourhoods in low elevations near rivers and drainages will be cooler, because cold air settles at the lowest points, and marginally hardy plants are more likely to freeze in those locations.

That is cold air drainage, and it is why two houses in the same zone on the same map lose different plants in the same February. Bloomington, the Virgin River bottoms and the ground along Santa Clara Creek all behave colder than the map implies. The address matters, not the town.

The same brochure argues that Sunset climate zones describe this place better than USDA does, because they account for growing season, summer heat and wind rather than winter minimums alone. Most of the county falls in Sunset zone 10, high desert, with hot summers, cold winters and up to 300 growing days a year across elevations from 3,300 to 5,000 feet. The higher communities fall into zone 2B, cooler in both directions, with about 160 growing days.

Where to look a plant up

Utah State University Extension publishes a statewide water-wise plant list too, and its definition of the term is worth carrying because it sets expectations precisely: water-wise plants, on average, need water approximately once every two weeks after establishment and still keep their appearance.

One caution about that statewide list. It is weighted toward northern Utah and headlines bigtooth maple, Gambel oak, serviceberry, white fir, Colorado spruce, Douglas-fir, kinnikinnick and lilac. Those are Wasatch Front plants. For Washington County, use the District and Red Hills sources first.

• The Washington County Plant Guide, published by WCWCD. Roughly 330 species that usually do well in the county's major population centres, each tagged by location, type and water need.
• The Red Hills Desert Garden plant finder. 310 plants, filterable by category, water need, USDA zone, flower colour and light, and flagged for Washington County natives and for what is actually growing at the garden. This is the best working tool for local design.
• WCWCD's Most Wanted Trees, February 2025. The District's own tree shortlist with size, exposure and water data.
• WCWCD's Reliable Perennials. A short list with the District's own notes on each plant.

The District's own ten trees

Read the District's notes before you fall in love with one. Arizona Velvet Mesquite carries stout thorns up to three inches long and its wide asymmetrical crown is, in the District's words, not conducive to small space restricted areas. Blue Ghost Eucalyptus is singled out for its lack of susceptibility to chlorosis, which is a bigger compliment here than it sounds. Desert Willow does best with just enough water to keep it blooming and healthily green through the warm months, which means it can be overwatered into a mess. Texas Red Oak is described as well adapted to our alkaline soils, and that phrase is doing real work.

Trees are also the highest-leverage thing you can plant. WCWCD publishes that shading keeps areas up to 25 degrees cooler, that shade trees can lower surface temperatures by up to 50 degrees, and that grass uses four times more water than trees and shrubs. A lawn feels cool because it is evaporating water you paid for. A tree is cooler and cheaper at the same time.

Perennials that hold up

The District's Reliable Perennials list is short and it is honest, including about maintenance. Blackfoot daisy, blanket flower, carpet rose, chocolate flower, coreopsis, creeping lantana, desert marigold, gaura, meadow sage, Mexican petunia, moss verbena, perky sue, Russian sage, red yucca, mealy cup sage and yarrow.

Read the notes as a calendar, because that is what they are. Gaura is cut back in late spring. Russian sage is cut back in spring, and the District calls it very hardy and happy in sun or shade. Meadow sage is cut back after flowering to renew it. Blanket flower, coreopsis, desert marigold, perky sue and moss verbena all want spent flowers removed. Red yucca throws flower stalks to six feet and pulls hummingbirds.

Two warnings in the District's own words. Desert marigold self-sows readily, though it is easily contained if you would rather it did not. Mint can be invasive if it is not contained, and in an irrigated bed it will not contain itself.

What people try that does not work

• Marginal zone 9 plants in a low, river-adjacent yard. The District says plainly that buying them is taking a risk, and cold air drainage is where that risk gets collected.
• Northern Utah plant lists. Colorado spruce and Douglas-fir do not tolerate a July average high of 101.9 degrees and 98 days over 100, which is what 2024 delivered here.
• Trees that chlorose on alkaline soil. USU states that high soil pH is common in Utah and causes problems with iron and manganese availability for trees. Pin oak, red maple, sweetgum, river birch and many silver maples yellow out here.
• Cool-season lawn as the default ground cover. Not a plant failure, an economic one, at four times the water of trees and shrubs.
• A thirsty plant dropped into a dry zone. USU's SLIDE plant factors make it arithmetic: a desert plant zone is designed at a plant factor of 0.3, while cool-season turf and annual flowers sit at 0.8. Put an 0.8 plant in an 0.3 zone and you either lose the plant or overwater everything around it.

Weeds, and the list that has legal force

Utah maintains a noxious weed list under the Utah Noxious Weed Act, administered by the Utah Department of Agriculture and Food. It is organised in classes: 1A and 1B for early detection and rapid response, 2 for control, 3 for containment, and 4 for species prohibited from sale.

Class 4 is the one that touches landscaping directly, because it names ornamental plants that may not legally be sold or propagated in Utah. Some plants that are still traded, and a few that appear on older county plant lists, sit close to that line. We check any species we are about to specify against the current list rather than against a nursery's inventory, because the list changes and the nursery's does not.

One species worth noticing by its absence: fountain grass does not appear in the Washington County Plant Guide at all. When a list this long leaves something out, that is usually a decision rather than an oversight.

There is no approved plant list for the rebate

This is the single most common misunderstanding about the District's landscape program, and it is worth stating flatly. The rebate does not dictate species. There is no approved plant list, and any contractor telling you a plant is or is not approved is describing something that does not exist.

What the program requires is a result: 50 percent living plant and tree cover at maturity across the converted area, free of grass. How you get there is a design question. WCWCD counts each tree toward that coverage at 350 square feet, so one tree carries the same weight as ten plants, and existing trees inside the conversion area count.

The District points people to its own Plant Guide, Most Wanted Trees, Reliable Perennials and the Red Hills Desert Garden database as recommendations. Recommendations, not requirements. That distinction is the difference between a design you like and a design a program picked for you.

More under water-wise landscape

• Artificial turf, measured: 200 degrees on a 98 degree day
• Defensible space, water savings and your wildfire fee
• Getting a Level 2 charger installed here