When people think of root rot, they usually blame overwatering or poor drainage. And while those are common culprits, there’s another, often overlooked cause: under-fertilising.
Yes, you read that right. Giving your plants too little fertiliser can directly contribute to root rot. Here’s how it works - and why it’s all about EC (electrical conductivity), water balance, and nutrient uptake.
Plants Don’t Just Drink Water - They Drink Nutrients
Plant roots absorb water through osmosis, a process that depends on the difference in EC (electrolyte concentration) between the plant’s cells and the surrounding mix. When the EC in the root zone is too low - meaning there are too few nutrients in the potting mix - water uptake slows dramatically.
In other words, roots need a minimum EC level to function properly. Without it, the plant can’t absorb water efficiently, even if the mix is wet. So instead of drawing moisture up into the plant, the water just sits there - cold, stagnant, and unused.
When Roots Stop Drinking, the Mix Stays Wet
Most growers assume a wet mix means the plant is well-hydrated. But if the plant isn’t absorbing water (due to low EC), the moisture doesn’t go anywhere. Over time, the potting mix remains too moist for too long, especially in low-light or cooler conditions.
This wet, oxygen-starved environment sets the stage for anaerobic bacteria and fungal pathogens, like Pythium and Phytophthora, to take over. Healthy roots start dying back. The plant declines. And now you have full-blown root rot, even though you didn’t overwater.
A Common Mistake: “I’m Not Fertilising Because My Plant Looks Unhappy”
Ironically, many people stop fertilising when their plant looks sick, thinking it needs a break. But in cases where the mix is staying wet and roots are dying back, this only makes things worse. The plant slows its uptake even further, causing a vicious cycle of:
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Low EC → poor water and nutrient absorption → wet mix → root dieback → even worse absorption → rot.
How to Prevent This
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Maintain a Balanced EC
Use a high-quality fertiliser at the appropriate strength, and apply it consistently. Even light feeders need some level of nutrients to maintain normal water uptake. -
Avoid Flushing Without Replenishing
Flushing can reduce salt build-up, but if you don’t follow it with nutrients, the EC drops too low. Always feed after flushing. -
Use a Well-Draining Mix
Even with proper feeding, a dense or soggy mix can hold too much water. Our HiGrow blends are designed to maintain aeration and structure, helping you avoid rot before it starts.
The Takeaway
Root rot isn’t always caused by “too much” - it’s caused by not enough. Plants rely on a baseline level of nutrients to absorb water and stay healthy. Skimping on fertiliser may seem harmless, but it can quietly undermine your plant from the roots up.
At HiGrow, we design our potting mixes to work with your feeding program- not against it. Just add nutrients, water smartly, and let your plants thrive.