Can overwatering cause plant diseases?
Written by
Julia Anderson
Reviewed by
Prof. Martin Thorne, Ph.D.Excessive moisture predisposes plants to diseases through disruption of the soil ecosystem. One client of Advanced Design lost 30 rosemary plants to root rot from watering every single day! The saturated soil suffocated the roots of the plants within a couple of days and pythium pathogens were able to kill the entire crop. It is essential to manage moisture levels so these pathogens don't get a foothold!
Root Suffocation Risks
- Oxygen levels drop below 6 mg/L in waterlogged soils
- Root hairs die within 48 hours of submersion
- Pathogen entry points form at damaged root zones
Fungal & Pest Explosion
- Fungus gnats: Lay 200+ eggs in damp topsoil
- Phytophthora: Spreads 1 inch/day in saturated conditions
- Slime molds: Thrive above 80% soil moisture
Nutrient Depletion
- Nitrogen leaching: 40% loss after 3-day saturation
- Iron chlorosis: Yellowing from poor uptake in wet soils
- Magnesium washout: Requires 6 weeks to replenish
Prevent waterlogging by using $20 moisture meters, which drill down 12 inches. I became an enthusiast with mine because it alerts me when I get above 60% saturation. For potted plants, instead of adding only water-retaining soil, mix in about 30% perlite with the potting soil. I reduced root rot cases by 75% during the trials in the nursery last year.
Do not throw away overwatered foliage, and recover them. Take the soil out of the pot, and look at the roots, after you remove them from the container. Carefully shake some mud off and snip off any blackened or mushy areas of the roots using sterilized shears. Repot the plant in an appropriate soil mix that contains pine bark fines for drainage. Water the plant after 7 days, this forces them to root before water becomes available.
Read the full article: Identify Plant Diseases: Detection & Control Guide
