Kratky Plant Wilting: Why a Plant in Water Droops

A plant that wilts while its roots hang in solution looks like a contradiction. In a Kratky kit it usually means the roots can take in water but not enough oxygen, or that they have been damaged. Here is how to work out which.

Why a plant can wilt in water

Roots need oxygen to work. Without it they cannot take up water and nutrients properly, however much water surrounds them. A Kratky kit has no pump, so its roots get oxygen from the air gap between the lid and the falling solution, and from oxygen dissolved in the water. Most wilting in a Kratky kit comes from one of those two supplies failing.

The five usual causes

Kratky wilting: causes and clues

Cause	Clues	Fix
Air roots drowned by a refill	Wilting started a day or two after topping up to the original line	Let the level fall, or pour some solution out until the upper roots are in air again
Warm solution	Wilts in the afternoon, recovers at night; reservoir in sun or near heat	Move to a cooler spot; shade or insulate the reservoir
Root rot	Brown, slimy, smelly roots	See Kratky root rot
Solution ran out	Roots no longer reach liquid	Add a little solution so the root tips reach it again
Heat or strong light on the leaves	Leaves droop at midday, roots healthy	Raise the light, add shade or move the kit

Drowned air roots

This is the classic Kratky mistake. As the solution level drops over the first weeks, the roots above it adapt to living in moist air. Topping the reservoir back up to where it started puts those roots under water, where they cannot get enough oxygen. The plant wilts within a day or two, and if the roots stay flooded they begin to rot. The fix is to restore the gap: pour off solution until the upper roots are out of the water again. The article on the Kratky air gap shows what the level should look like over a crop.

Warm solution

Cool water holds more dissolved oxygen than warm water, and warm roots need more of it. A reservoir in a sunny window, on top of a fridge or under a hot light can get warm enough for the plant to wilt in the hottest part of the day. Feel the side of the container: if it is warm to the touch, move it, shade it or wrap it in a light-colored sleeve. Afternoon wilting that recovers overnight is a strong sign of heat.

Solution ran out

Late in a crop, a large plant can drink the reservoir down below its root tips. The plant wilts because it has no water at all. Add a small amount of freshly mixed solution so the lowest roots reach it, without covering the upper air roots. The guide on how often to refill a Kratky kit explains how much to add.

Heat and light stress

Sometimes the roots are fine and the leaves simply lose water faster than the roots can supply it on a hot day or under a light that is too close. Lettuce is especially prone. Raise the light, increase the distance from a hot window, or improve air flow. Plants that wilt only in the hottest hours and look fine by morning are often in this group.

Wilting just after transplant

Seedlings often droop for a day or two after moving into a kit, especially if they were started in soil or the roots were disturbed. Make sure the bottom of the net pot touches the solution so the roots can reach it, keep the young plant out of strong direct sun for a few days, and give it time. If it is still wilting after several days, check that the grow media is wet from the bottom up. The guide to Kratky seed starting covers transplanting.

How to check without harming the plant

1. Note when the wilting started and what changed (a refill, a move, a hot day).
2. Lift the lid slowly and look at the roots and the level.
3. Feel the reservoir for warmth.
4. Smell the solution; sour or rotten means trouble.

The Kratky problems and fixes guide has the full diagnostic order for other symptoms.

Frequently asked questions