A palette signed off against design intent, procured and installed can still fail in its second summer because the irrigation water carries more salt than the species can hold. The cost lands after handover, in replacement plants, remedial drainage and a maintenance contractor blamed for a design decision. Test the water before the schedule is fixed.
EC and TDS are the numbers that matter
Electrical conductivity (EC) is the working measure of salinity, in decisiemens per metre (dS/m). Total dissolved solids (TDS) states the same property in milligrams per litre, and the two convert at roughly 1 dS/m to 640 mg/L. Ask for both: specifications and lab reports use them interchangeably.
Below about 0.7 dS/m there is no salinity restriction on most ornamental planting. Between 0.7 and 3.0 dS/m the palette narrows. Above 3.0 dS/m only genuinely salt tolerant species hold form. EC alone is not enough: sodium adsorption ratio, chloride, bicarbonate and boron all need reporting. Chloride scorches foliage before EC predicts it; boron is toxic at low mg/L.
Why potable assumptions fail
Design teams often assume desalinated potable supply and treat salinity as a non-issue. That holds at handover, rarely for the life of the asset. Allocations get trimmed, and landscape irrigation is the first demand moved to an alternative source. When the blend ratio moves, EC at the emitter moves with it.
Treated sewage effluent is mandated on many schemes, but it is not a single product. Tertiary effluent from a well run plant is moderate in salinity and high in nitrogen. From a plant above design load it carries higher EC, variable sodium and disinfectant residual. Ask for twelve months of discharge data, not one certificate, and design to the worst month.
Leaching fraction and salt in the root zone
Salt applied in irrigation does not leave with the plant. Water evaporates and transpires, salts stay behind, and root zone salinity climbs to a multiple of the applied figure until something flushes it. The leaching fraction, the share of applied water draining past the roots and carrying salt away, holds the balance stable.
Moderately saline water on a free draining sandy profile may need 15 to 20 per cent of applied volume as leaching, and poorer water more. Irrigation demand therefore exceeds plant water requirement, and drainage must take the leachate. Where earthworks leave a compacted layer, the allowance becomes a salt bath, so drainage failures masquerade as species failures.
Which species tolerate what
- Phoenix dactylifera and Washingtonia robusta: dependable on saline irrigation, holding condition where broadleaf trees decline.
- Conocarpus lancifolius (Damas): high tolerance of salinity and poor soils, but needs pruning to stay in scale.
- Ziziphus spina-christi (Christ's Thorn Jujube): native, deep rooted and comfortable on brackish supply.
- Olea europaea: moderately to highly tolerant, a reliable structural choice on blended sources.
- Delonix regia and Lagerstroemia speciosa: moderate at best, so place them where water and drainage are proven.
Our note on drought, salt and frost tolerant plants covers wider groupings; the species index holds the records.
Practical checks before the palette is fixed
- Sample the water you will actually use: at the emitter or the tank, not the incoming main, and repeat summer and winter.
- Ask for the full suite: EC, TDS, pH, sodium adsorption ratio, chloride, bicarbonate, boron and nitrate. One EC figure is not a report.
- Test the backfill, not just the subgrade: imported sand and manufactured topsoil carry their own salinity.
- Confirm drainage before agreeing a leaching fraction: percolation tests, plus a check for construction compaction.
Ornatec supplies mature trees, palms and shrubs at project scale, with species advice matched to the water and soil on your site. Review our consultancy services, see how a project runs from specification to delivery, or send your plant schedule and water analysis for review.
For salinity constrained schemes, see our drought tolerant trees, the top picks for the Middle East, and trees for Middle Eastern landscapes.