# Salt build-up

> Salt build-up is the accumulation of unused fertiliser and water salts in the growing medium, raising root-zone EC and causing osmotic stress and lockout-type symptoms.

- Canonical: https://genetixbay.com/knowledge/glossary/salt-build-up.html
- Also written: salt buildup, salt accumulation, salt build up, fertiliser salt build-up, fertilizer salt buildup, salt crust
- Glossary category: pH, EC and water · Evidence: Established
- Status: Draft: awaiting expert review · Updated: 2026-10-31
- Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary"

Salt build-up happens when more dissolved ions go into the medium than the plant takes up or the [drainage](https://genetixbay.com/knowledge/glossary/runoff.md) carries away. Water evaporates and is transpired, salts stay behind, and the concentration in the pore water climbs. Sodium, chloride, sulfate and bicarbonate from [hard water](https://genetixbay.com/knowledge/glossary/general-hardness.md) accumulate especially, because plants use little of them.

## In practice

Signs: runoff [EC](https://genetixbay.com/knowledge/glossary/ec.md) well above input EC (often by 1 mS/cm or more), white crust on the medium surface or pot edges, crisped leaf tips and margins, slowing growth, drooping despite moist medium, and deficiency-like symptoms because high salinity and imbalanced ions block uptake.

Causes: low or no runoff in coco and soilless media, high-EC feeding, [hard tap water](https://genetixbay.com/knowledge/glossary/tap-water.md) and infrequent large waterings that let the medium dry hard between them.

Fix: a [root-zone flush](https://genetixbay.com/knowledge/glossary/root-zone-flush.md) with enough volume (often two to three times the [pot volume](https://genetixbay.com/knowledge/glossary/pot-size.md)) of a mild, pH-adjusted nutrient solution or plain water, then resume feeding at a moderate EC with regular runoff of about 10–20%. Check that runoff EC falls back towards input.

## Don't confuse with

- **Nutrient burn**: [tip burn](https://genetixbay.com/knowledge/glossary/nutrient-burn.md) from a single over-strong feed.
- **Pre-harvest flush**: an unrelated ritual GenetixBay rejects.

## Myth check

GenetixBay house position: a **root-zone flush** to wash accumulated salts out of the medium is the one valid [flush](https://genetixbay.com/knowledge/glossary/flushing.md). It treats the medium, not the plant, and can be done at any stage. A **pre-harvest flush** is a *Myth* and actively harmful: it starves the plant while it is packing on its final weight and resin. See [the flush debate](https://genetixbay.com/knowledge/harvest-cure/flush-debate.md).

## Related terms

[Runoff EC](https://genetixbay.com/knowledge/glossary/runoff-ec.md), [Osmotic stress](https://genetixbay.com/knowledge/glossary/osmotic-stress.md), [Nutrient lockout](https://genetixbay.com/knowledge/glossary/nutrient-lockout.md), [Runoff](https://genetixbay.com/knowledge/glossary/runoff.md), [Tap water](https://genetixbay.com/knowledge/glossary/tap-water.md)

## Read more

- [Runoff testing: how to measure root-zone pH and EC and what the numbers mean](https://genetixbay.com/knowledge/ph-ec/runoff-testing.md)
- [Pre-harvest flushing: a myth that costs you yield and resin](https://genetixbay.com/knowledge/harvest-cure/flush-debate.md)

## Sources

1. Sonneveld C, Voogt W. 2009. Plant Nutrition of Greenhouse Crops. Springer. https://doi.org/10.1007/978-90-481-2532-6
2. Cavins TJ, Whipker BE, Fonteno WC, Harden B, McCall I, Gibson JL. Monitoring and managing pH and EC using the PourThru extraction method. NC State University Horticulture Information Leaflet 590. Cited via MSU Extension: https://www.canr.msu.edu/uploads/resources/pdfs/measuring_ph_and_ec_of_crops_grown_in_large_containers.pdf