A Kratky garden is a simple way to grow a plant. There is no pump and no electricity.
Kratky Problems
Kratky yellow leaves have several possible causes, and some of them are perfectly normal. The best clue is where the yellow appears: on the oldest leaves at the bottom, on the newest leaves at the top, between the veins, or all over the plant. Read the pattern first, then check the likely causes in order.
When the lowest, oldest leaves turn yellow one at a time while the rest of the plant looks healthy, it is often normal aging. Plants move resources from old leaves into new growth. Pick off the yellow leaves so they do not fall into the container.
If many older leaves yellow quickly, the plant may be short of nutrients, especially nitrogen, which plants move from old leaves to new ones when supply runs low. Check that the nutrient was mixed at the label rate for leafy growth.
A plant that is pale green or yellow all over, and often tall and thin, usually needs more light. Move it to a brighter spot or add a grow light, as described in Step 5: Watch it grow.
Pale all over can also mean the nutrient is too weak, or that the pH is outside the range the plant can use, so it cannot take up nutrients even though they are in the water.
When new leaves come in yellow with green veins, a common cause is a problem taking up iron or other micronutrients, which is often linked to pH. Check the pH and adjust it to the range on your nutrient label. Using a complete hydroponic nutrient, not a soil fertilizer, matters here too. More on pH in Nutrients, pH and Safety.
If yellow leaves come with wilting, look at the roots right away. Roots that no longer reach the water, or roots that are brown and slimy, cannot supply the leaves. Kratky Root Rot explains what to look for, and Step 4: Check the water level covers the water level.
If you think the nutrient is too weak, check your measurements against the label for the volume of water you actually have. Small containers need small amounts, so a measuring mistake makes a big difference. If a lot of water has been used, topping up with a little nutrient solution at the label rate, rather than plain water, can help. Do not add extra nutrient on top of the label rate: too strong a solution can burn roots and leaf edges.
Late in a grow, the container may be running low and the nutrient may be mostly used up. Some yellowing of older leaves at this stage is common. If the plant is close to ready, harvest it. Step 6: Pick and enjoy explains when and how.
Brown, crispy leaf edges can mean the solution is too strong or the plant is too hot. Spots, holes or sticky leaves can mean insects. If you see these instead of plain yellowing, see the full list on Kratky Problems.
Leaves can also bleach or yellow from too much heat or intense light close to the plant, such as a grow light hung too low or a jar pressed against hot glass. Raise the light, or move the container back from the window, and watch whether new leaves come in green.
Pick off leaves that are fully yellow or dying. They will not turn green again, and removing them keeps them from falling into the container and breaking down in the water. Leave leaves that are only slightly pale while you fix the cause; they may still help the plant.
Write down what you checked and what you changed, with the date. Yellowing usually takes days to improve, because the plant has to grow new leaves. Notes stop you changing too many things at once, and help you spot the cause next time.
Once the cause is fixed, look at the new leaves, not the old ones. New growth coming in green is the sign that the change worked.
Tip: Take a photo of the plant each week. Comparing photos shows when the yellowing started and what changed.
Nutrients, pH and safety guide