Secondary Water, Alkaline Soil, and Plant Selection in Utah

What secondary water is

Secondary water — also called secondary irrigation water or pressurized secondary — is untreated water distributed through a separate pressurized system alongside culinary (drinking) water. It is used exclusively for outdoor irrigation. Many Utah communities in the Salt Lake Valley and surrounding areas have secondary water systems, including parts of Riverton, South Jordan, Herriman, Bluffdale, Lehi, and other municipalities.

Secondary water is typically sourced from snowmelt, reservoirs, and canals. Because it is not treated to drinking water standards, it retains naturally occurring minerals, sediment, and dissolved solids at higher concentrations than culinary water. The specific chemistry varies by source and delivery system.

How secondary water affects soil chemistry

Utah's soils are already alkaline — pH values of 7.5 to 8.5 are common in residential landscapes across the Salt Lake Valley. Secondary water tends to be higher in calcium carbonate, magnesium, and other dissolved minerals than culinary water. Over time, irrigating with secondary water can increase soil alkalinity and contribute to calcium carbonate accumulation in the root zone.

Elevated soil pH reduces the availability of iron, manganese, zinc, and other micronutrients. Plants that require acidic conditions — including many popular ornamentals such as azaleas, rhododendrons, and pin oaks — will show chlorosis (yellowing leaves) and decline when grown in alkaline soil irrigated with secondary water. The problem is not a lack of nutrients in the soil; it is that the nutrients are chemically unavailable at high pH.

Attempting to acidify soil through amendments is generally not a practical long-term solution in Utah landscapes. The buffering capacity of alkaline soils and the ongoing mineral input from secondary water irrigation will counteract acidifying amendments over time. Selecting plants that tolerate or prefer alkaline conditions is the more reliable approach.

Plants that perform well with secondary water

The following plant categories are well-suited to Utah landscapes irrigated with secondary water. All tolerate alkaline soil conditions and are available through Utah nurseries.

• Native shrubs: rabbitbrush (Ericameria nauseosa), Apache plume (Fallugia paradoxa), fernbush (Chamaebatiaria millefolium), fourwing saltbush (Atriplex canescens), and big sagebrush (Artemisia tridentata) are all native to the Intermountain West and evolved in alkaline soil conditions.
• Drought-tolerant perennials: Russian sage (Perovskia atriplicifolia), catmint (Nepeta spp.), yarrow (Achillea millefolium), penstemon (Penstemon spp.), and blanket flower (Gaillardia spp.) all tolerate alkaline soil and perform well with reduced irrigation once established.
• Ornamental grasses: blue oat grass (Helictotrichon sempervirens), Karl Foerster feather reed grass (Calamagrostis × acutiflora), and blue grama (Bouteloua gracilis) tolerate alkaline soil and moderate drought.
• Shade trees: hackberry (Celtis occidentalis), bur oak (Quercus macrocarpa), honeylocust (Gleditsia triacanthos var. inermis), and Chanticleer pear (Pyrus calleryana 'Chanticleer') all tolerate alkaline soil and urban conditions.
• Conifers: Colorado blue spruce (Picea pungens), Austrian pine (Pinus nigra), and Rocky Mountain juniper (Juniperus scopulorum) are reliable in alkaline soil conditions.

Plants to avoid with secondary water

Acid-loving plants will struggle in Utah landscapes irrigated with secondary water. The following are commonly planted but perform poorly in alkaline conditions:

• Pin oak (Quercus palustris): develops severe iron chlorosis in alkaline soil; bur oak or chinkapin oak are better alternatives.
• Azalea and rhododendron: require acidic soil; will not thrive in Utah's alkaline conditions regardless of irrigation source.
• River birch (Betula nigra): tolerates some alkalinity but is prone to chlorosis in high-pH soils; hackberry is a more reliable alternative.
• Sweetgum (Liquidambar styraciflua): prone to iron chlorosis in alkaline soil.
• Gardenia: requires acidic soil; not suitable for Utah landscape conditions.

Irrigation system considerations

Secondary water systems typically operate on a seasonal schedule — they are pressurized in spring and shut down in fall. This means secondary water is not available for winter irrigation or for establishment watering outside the irrigation season. New plantings installed in fall may need culinary water for establishment if secondary water has been shut off.

Secondary water pressure and flow rates can vary by system and time of day. Irrigation system design for secondary water should account for the specific pressure and flow characteristics of the local system. Drip irrigation is generally more efficient than spray irrigation for planting beds, regardless of water source.

Some secondary water systems have restrictions on the types of irrigation equipment that can be connected. Check with your local secondary water provider before installing or modifying an irrigation system.

Soil preparation and long-term management

Incorporating organic matter into planting beds before installation improves soil structure and can modestly buffer pH over time. Compost, aged wood chips, and other organic amendments improve water retention and drainage while providing a slow source of nutrients.

Mulching planting beds with organic material — wood chips, shredded bark — reduces evaporation, moderates soil temperature, and adds organic matter as it decomposes. This is beneficial in any Utah landscape but is particularly useful in areas irrigated with secondary water, where soil chemistry management is an ongoing consideration.

Iron chelate supplements can address iron chlorosis in established plants, but they are a management tool rather than a solution. If a plant consistently requires iron supplementation to maintain healthy foliage, it is likely not the right plant for the site.