Hydroponic Plant Problems? Start Here.
When a plant in your hydroponic tower starts looking unhappy, the useful question is not simply “what is wrong with it?” It is “what is the plant telling me, and what changed?”
A yellow leaf does not automatically mean more nutrient. A droopy plant does not always need more water. And one struggling lettuce amongst a tower of healthy plants is telling you something quite different from every plant suddenly looking miserable.
So before changing everything at once, start with the clues you already have.
This is the troubleshooting process we use with our own FlowGrow towers.
Start with two questions
If one plant is struggling while its neighbours look healthy, start with that plant. If several plants change together, look at the wider system and growing environment.
Think back over the last few days. A reservoir refill, nutrient change, transplant, warmer weather, lower water level or a move to a different position can all give you useful clues.
Those two questions can stop you adjusting an entire reservoir because of one grumpy lettuce.
Our troubleshooting rule: observe first, measure what you can, then change one thing at a time.
1. Check the water level and circulation
Start with the simple stuff.
Can you hear the pump running? Is water reaching the top of the tower and flowing back through the planting sites? Is there enough water in the reservoir for the pump to circulate properly?
In a FlowGrow tower, nutrient solution is pumped to the top, spread through the Flow Cap and allowed to flow down past the roots before returning to the reservoir. If that circulation stops, plants cannot access water and nutrients in the way they normally would.
Quick water-flow check
- make sure the pump is running
- check the reservoir has enough water
- check the tubing has not disconnected or kinked
- make sure water is reaching the Flow Cap
- check the Flow Cap outlets and planting pockets are flowing normally
- look for large root masses or debris that may be restricting circulation
Water use can change surprisingly quickly. A young tower may barely move the reservoir level, while larger plants and warm weather can use considerably more. Do not judge today's water use by what the tower needed a month ago.
2. Check the nutrient solution
Plants growing hydroponically rely on the reservoir for the minerals they would normally obtain through soil. But more nutrient is not automatically better.
Our FlowGrow nutrient measurements are designed around a regular rhythm that includes a fresh nutrient solution approximately every two weeks. That gives the reservoir a clean reset rather than endlessly topping up and trying to correct an increasingly complicated mix.
The important thing to remember is that the solution does not stay exactly as you mixed it. Plants take up water and nutrients at different rates, and those demands change as plants become larger, the weather warms or the mix of crops in the tower changes.
A tower full of young lettuce will not necessarily behave like a tower supporting established tomatoes and other fruiting plants.
If something is not looking right, ask what happened since the last reservoir change. Has the water level dropped significantly? Did you recently add nutrient? Are the plants much larger than they were two weeks ago?
For the FlowGrow feeding amounts and when to use Grow or Bloom, see our FlowGrow Feeding Guide.
3. Measure EC and pH before you start guessing
If a plant problem has you wondering whether the reservoir is too strong, too weak or sitting outside a useful pH range, this is where measuring helps.
EC gives you an indication of the overall concentration of dissolved salts in the nutrient solution. pH affects how available those nutrients are to the plant.
For FlowGrow we generally aim for a pH of around 5.5 to 6.5. EC needs more context because different crops and stages of growth can place different demands on the reservoir.
An EC reading does not tell you exactly which nutrient a plant is using more or less of. It does, however, give you much better information than adding extra nutrient because a leaf looks pale.
Measure before you adjust. If you use a meter, take the reading from well-mixed reservoir water and look at EC, pH, plant symptoms and recent changes together.
If you want to measure rather than guess, we stock the Bluelab Conductivity Pen for checking EC and the Bluelab pH Pen for checking pH.
We explain both measurements more fully in Understanding What pH and EC Mean.
4. Look at the roots
Roots can tell you a lot, but do not diagnose them by colour alone.
Healthy new hydroponic roots are usually light or white and firm. Seeing fresh white roots developing is one of the nicest signs that a plant is settling in and actively growing.
If you have transplanted a plant from soil, its older roots may already look darker even after the potting mix has been rinsed away. We have also noticed some staining of older roots after plants have been growing in nutrient solution for a while. A root system that is not perfectly white does not automatically mean root rot.
What matters is the combination of signs.
New white growth
Fresh light-coloured roots growing alongside older darker roots, with the plant continuing to grow well.
Declining root condition
Dark roots that are also soft or slimy, smell unpleasant, have little fresh white growth and are accompanied by a declining plant.
For newly transplanted seedlings, also check that young roots are reaching the moisture flowing through the tower. If the roots have become very large, check they are not restricting water flow through the planting pocket or tower.
If your seedling came from potting mix, our garden centre seedling guide shows how we prepare and rinse roots before planting them into FlowGrow.
5. Read the leaves, but look for a pattern
Leaves are usually where we notice trouble first.
Yellowing, brown edges, spots, curling, holes and wilting can all tell you something, but very few leaf symptoms have only one possible cause.
Instead of asking only “What does a yellow leaf mean?”, ask which leaves are changing, how many plants are affected and what else has changed.
An older outside lettuce leaf gradually yellowing on an otherwise vigorous plant is very different from new growth becoming pale across several planting sites.
Look at the whole picture
- old leaves or new growth?
- one plant or several?
- slow change or sudden change?
- healthy new roots or declining roots?
- recent nutrient or reservoir change?
- enough useful light?
The pattern matters more than trying to match one leaf colour to one nutrient deficiency.
6. Check where the tower is sitting
Hydroponics changes how plants receive water and nutrients. It does not remove their need for light.
A room can look beautifully bright to us while providing much less useful light than a plant needs. Look at where your tower actually sits during the day. How long does useful light reach the plants? Is one side receiving much more than the other? Has the sun moved with the season?
Stretching towards a window, long weak growth, pale leaves or consistently slow development can all be reasons to reassess the position.
This is also where the wheels on a FlowGrow tower are genuinely useful. You can reposition the tower as light changes around your home or move it away from an excessively hot position during summer.
For a deeper look at light and position, read Where Should I Place My Tower?
7. Think about temperature as well as light
Light and heat need to be considered together.
Fruiting plants such as tomatoes need plenty of light, but a tower beside a hot sun-facing wall or sitting on heat-reflecting paving can create a very different environment around the reservoir and roots.
Lettuce can also respond quickly to hot conditions, with wilting or bolting becoming more likely as temperatures rise.
If your tower has been growing happily and several plants start behaving differently during a run of hot weather, do not immediately assume the nutrient mix is wrong.
Our Keeping Your Hydroponic Tower Cool in Summer guide covers reservoir shade, water checks, repositioning and the simple cooling tricks we use at home.
8. Look for pests
No soil does not mean no bugs.
Aphids, caterpillars and other garden visitors can still find hydroponic plants, particularly outdoors. Look underneath leaves and around fresh new growth rather than only inspecting the top of the plant.
Holes, distorted new leaves, sticky residue or visible insects point you towards a pest problem rather than something happening inside the reservoir.
We cover the common questions in Do FlowGrow Towers Get Bugs?
9. Check whether the plant simply needs harvesting
Sometimes a plant is not struggling. It is just ready.
Leafy greens grown for repeated harvesting benefit from regular picking. Other plants may eventually be better harvested completely and replaced with a fresh seedling.
If a plant has become oversized, crowded or is shading everything around it, the solution may be less troubleshooting and more lunch.
Change one thing at a time
When something looks wrong, it is tempting to add nutrients, adjust the pH, move the tower, clean the reservoir and change the pump setup all at once.
Then, if the plant improves, you have absolutely no idea what fixed it.
Observe → check → measure → change one thing → watch what happens.
Hydroponic growing gets much easier when you stop treating every unusual leaf as an emergency and start looking for patterns.
Your FlowGrow troubleshooting order
- One plant or several?
- What changed recently?
- Is there enough water and is it circulating normally?
- When was the nutrient solution last refreshed?
- What do EC and pH tell you?
- What do the roots look and feel like?
- What pattern are the leaves showing?
- Is the tower getting enough useful light?
- Has the temperature or weather changed?
- Are there signs of pests?
- Is the plant simply mature and ready to harvest?
You do not need to become a plant scientist. You just need a repeatable way to eliminate the obvious things first.
When one plant does not make it
Sometimes you can check everything and still lose a plant.
Seedlings are not identical. Roots can be damaged during transplanting. One plant may establish poorly while the plants beside it thrive.
If the rest of your tower is growing well and one plant continues to decline, removing it and starting another seedling can be the most sensible answer.
A hydroponic tower is not a test you have to pass. It is a garden.
And gardens occasionally have opinions.
The more you grow, the easier this gets
Your first yellow leaf can feel significant.
After a few rounds of lettuce, herbs and other crops, you start recognising what is normal for your tower. You notice how quickly the reservoir drops in warm weather, which side gets the strongest light, when lettuce wants harvesting and what healthy new root growth looks like.
That is where confidence comes from. Not from never having a plant struggle, but from knowing what to check when one does.
Frequently asked questions
Why are my hydroponic leaves turning yellow?
Yellow leaves can have several causes, including natural ageing, light, nutrient strength, pH and root health. First check whether the yellowing affects old or new leaves, one plant or several, then check recent changes, EC, pH and roots before adjusting the reservoir.
What should healthy hydroponic roots look like?
Fresh healthy root growth is generally light or white and firm. Older roots may be darker, particularly after transplanting from soil, and some staining can develop over time. Dark colour alone does not diagnose root rot; texture, smell, fresh root growth and the condition of the plant matter too.
How often should I change the nutrient solution?
Our FlowGrow feeding rhythm is built around refreshing the nutrient solution approximately every two weeks, with water topped up as plants use it. Plant size, crop type and warm weather can all change how quickly water and nutrients are used.
Should I add more nutrient when a plant looks pale?
Not automatically. Pale growth can have several causes. Check the pattern, light, roots, EC and pH first. Measuring before adjusting gives you more useful information than adding nutrient based on leaf colour alone.
Can one unhappy plant mean the whole reservoir is wrong?
Not necessarily. If one plant is struggling while the rest of the tower looks healthy, start by checking that individual plant and its roots. When several plants develop similar symptoms together, the wider system and growing environment become more likely suspects.
Helpful next steps
If one of your checks points to a particular area, these guides take you deeper without making you troubleshoot everything at once.
Understand pH and EC
Learn what the readings mean and how they help you understand your reservoir.
Cleaning & care
Keep the reservoir, pump and tower clean and running well.
More troubleshooting
Browse FlowGrow guides for common growing problems and plant-health questions.
The source of truth
We combine what we learn from growing in our own FlowGrow towers with established horticultural guidance. Technical references used in this guide:
Something not looking right?
Start with the simple checks, measure before you adjust, and let the plant give you clues.
