Keeping Your Hydroponic Tower Cool in Summer
A sunny spot is usually exactly what we're looking for when deciding where to grow.
Then summer arrives.
The patio heats up, the afternoon sun shifts further around the house, and suddenly the same spot that was perfect a few months ago is getting considerably warmer.
For hydroponic growing, there's another part of the picture too.
It's not only the plants sitting in the sun. The water inside the reservoir is warming up as well.
That doesn't mean your tower needs to spend summer hiding in the shade. Plants still need good light, particularly strawberries, chillies, tomatoes and other fruiting crops.
It's more about finding the balance between giving your plants the light they need and stopping the reservoir from becoming unnecessarily hot.
And, as we've discovered growing with FlowGrow, sometimes the simplest solutions are surprisingly effective.
Why does reservoir temperature matter?
Plant roots need more than water and nutrients.
They need oxygen too.
As water gets warmer, its ability to hold dissolved oxygen decreases. Prolonged high root-zone temperatures can also affect root function, plant growth and increase the risk of some root problems.
You don't need to spend summer chasing a perfect temperature, though.
For everyday home growing, around 18–24°C is a useful range to aim for. Different plants have slightly different preferences, so think of that as a comfortable working range rather than a magic number.
Once the reservoir starts heading towards 27°C and above, it's worth paying a little more attention and taking some simple steps to reduce the heat.
The useful goal: not perfect water temperature. Just stop the reservoir from becoming unnecessarily hot.
Start by keeping direct sun off the reservoir
This was one of those FlowGrow lessons that became obvious once we started growing through warmer weather.
Our reservoir is black.
That's useful because keeping light away from nutrient-rich water helps discourage algae growth inside the reservoir.
But there's a summer trade-off.
Dark surfaces also absorb solar heat.
Leave the black reservoir sitting in strong direct sun and it can absorb considerably more heat than we'd like.
My solution isn't particularly sophisticated.
I cover mine with a light-coloured towel.
A light-coloured towel or cover shades the black surface and reflects more of the sun's energy instead of allowing the reservoir to absorb it directly.
It doesn't require changing the tower. It doesn't interfere with growing. And you can take it off again when you don't need it.
Shade the outside, keep the inside dark
That's really the principle we're working with. Keep light away from the nutrient water inside, while protecting the dark outside of the reservoir from unnecessary direct summer sun.
Look at what's around your tower too
Sometimes the sun isn't the only source of heat.
Paving can become extremely warm during summer. So can decks, concrete and walls that have been sitting in direct afternoon sun.
Those surfaces can continue radiating heat around the tower even when the air temperature itself doesn't seem particularly extreme.
It's worth looking at the whole position rather than just asking, does this spot get enough sun?
Put your hand against the wall behind the tower on a hot afternoon. Feel the paving beneath it. Look at where the late-afternoon sun actually lands.
Homes create their own little pockets of heat, and sometimes moving half a metre makes more difference than you'd expect.
If you're still choosing a position, our guide to where to place your FlowGrow tower is a useful next read.
The best summer position might not be the best spring position
The sun doesn't stay in the same place throughout the year.
Its path changes with the seasons, which means a corner that receives lovely gentle sun earlier in the year can behave quite differently by midsummer.
This is where one small FlowGrow feature becomes particularly handy.
The tower has wheels.
You don't have to decide where your tower lives and leave it there forever.
If strong afternoon sun starts hitting the reservoir, move it slightly. If a nearby wall is becoming very hot, pull the tower away from it. If another part of your patio gets good morning light but afternoon shade, that might become the better summer position.
You can adjust the position again as the season changes.
The plants need light. The reservoir doesn't need to sunbathe.
When it's already hot, raid the chilly bin
This might be my favourite summer FlowGrow trick.
If the reservoir water has become warmer than I'd like, I use a sealed chilly-bin ice block.
Straight from the freezer and into the reservoir.
It provides temporary cooling without adding anything to the nutrient solution. Once that block has warmed up, you can swap it for another frozen one.
Keeping two in rotation makes this particularly easy during a run of very hot days.
Why sealed rather than loose ice? Loose ice eventually becomes extra water and can dilute the nutrient solution. A sealed ice block cools the reservoir without changing the water volume as it melts.
No fancy cooling system required.
Sometimes the chilly bin has already solved the problem.
Don't let the reservoir get too low
Plants can get surprisingly thirsty as they become larger, particularly during warm weather.
That makes regular water checks more important in summer.
There's another reason not to leave topping up until the reservoir is nearly empty.
A larger volume of water changes temperature more slowly than a small volume.
When there's plenty of water in the reservoir, it has more thermal mass. As the water level drops, that smaller volume can respond more quickly to the heat around it.
So during hot spells, don't wait for the reservoir to become very low before topping it up.
Check the gauge more frequently. You'll soon get a feel for how quickly your particular combination of plants is drinking, and don't be surprised if that changes considerably as they grow.
A droopy plant isn't necessarily a hungry plant
You walk outside on a hot afternoon and one of your plants looks decidedly unimpressed with life.
The temptation can be to think: it needs something.
And in hydroponics, “something” can easily get interpreted as more nutrient.
But heat can cause plants to wilt even when nutrients are available. On hot or windy days, leaves can lose water faster than the roots can replace it, and warm root-zone conditions can also affect how well roots function.
So before reaching for the nutrient bottle, check the simple things first.
- What's the reservoir level?
- How warm is the water?
- Has the tower been sitting in unusually strong sun?
- What do the roots look like?
- Does the plant recover as the day cools?
Observe first. Then adjust what actually needs adjusting.
If you do need to review feeding, our FlowGrow Feeding Guide explains the normal tower mix and when a gentler dose makes sense.
Summer is a good time to look inside the tower
Most of the time we're looking at what's happening above the planting sites.
Summer is a useful reminder to occasionally look below them too.
When you're checking the reservoir, have a look at the roots and water condition. Healthy roots give you useful clues about how things are going.
If something suddenly looks or smells noticeably different, don't ignore it and hope the leaves sort themselves out.
Warm conditions make good reservoir habits more important, not more complicated.
Keep the reservoir covered. Keep light away from the nutrient water. Top up regularly. Clean the system when needed. And have a look inside occasionally.
For the full clean-and-care process, see our Hydroponic Tower Maintenance guide.
When your tower becomes a jungle
There's a lovely point in summer when the tower you were patiently waiting to fill out suddenly seems to have plants everywhere.
Leaves overlap.
Basil starts taking liberties.
A tomato decides three planting sites are actually its personal territory.
It's a good problem to have.
But very dense growth can reduce airflow through the plants.
Regular harvesting helps. So does removing tired leaves and giving larger plants a little guidance or support where necessary.
You don't need to aggressively prune everything.
Just don't be afraid to eat your garden.
That's what it's there for.
Fruiting plants create an interesting summer balancing act
Strawberries, chillies and compact tomatoes generally want stronger light than leafy greens.
Which creates an obvious little puzzle.
You want sunlight on the plant.
You don't particularly want intense sunlight heating the black reservoir underneath it.
The answer isn't necessarily to move the entire tower into deep shade.
Instead, separate the two problems.
Give the plants useful light
Fruiting plants need enough light to support flowering and fruit production.
Protect the reservoir from heat
Shade the black reservoir, reposition the tower when useful, and cool the water temporarily during particularly hot spells.
You aren't trying to make summer disappear.
You're just helping the root zone stay a little more comfortable while everything above it enjoys the season.
If you're deciding what to plant, see What Can You Grow in a Hydroponic Tower?
What we've learned from growing FlowGrow through summer
Perhaps the biggest lesson is that summer growing doesn't need an elaborate cooling setup.
Most of the useful things are small.
Notice where the sun moves.
Keep an eye on the water level.
Shade the black reservoir.
Move the tower if its position becomes too hot.
Have a look at the roots occasionally.
Harvest enough to keep air moving.
And keep a couple of chilly-bin blocks in the freezer for those properly hot days.
A hydroponic tower is still a garden.
And gardens change with the weather.
Learning to notice those changes is part of the fun.
Frequently asked questions
What temperature should a hydroponic reservoir be in summer?
For everyday home growing, around 18–24°C is a useful working range rather than a strict target for every crop. Once nutrient water starts approaching 27°C and above, it's worth taking simple steps to reduce unnecessary heat.
Why is hot reservoir water a problem?
Warmer water holds less dissolved oxygen, while plant roots need oxygen for healthy function. Prolonged excessive root-zone temperatures can also affect plant growth and contribute to conditions that favour root problems.
Can I put ice in my hydroponic reservoir?
A sealed frozen chilly-bin ice block can be used for temporary cooling without adding water to the nutrient solution. We prefer this to loose ice because melting loose ice changes the water volume and can dilute the reservoir.
Should I put my hydroponic tower in the shade during summer?
Not necessarily. Plants still need useful light, particularly flowering and fruiting crops. Instead, look at whether you can shade the reservoir itself or reposition the tower to avoid the harshest afternoon heat while keeping useful light on the plants.
Why does my hydroponic tower use more water in summer?
Larger plants and warmer, brighter conditions can increase water use through transpiration. Check the reservoir more frequently during warm weather rather than relying on the same topping-up schedule all year.
Does a black hydroponic reservoir get hotter in the sun?
Dark surfaces absorb more solar radiation than light-coloured surfaces. FlowGrow's opaque black reservoir helps keep light away from the nutrient solution, but shading the outside during strong summer sun can help reduce additional solar heat gain.
Should I add more nutrients if my plants wilt in hot weather?
Not automatically. Heat and water stress can cause wilting even when nutrients are available. Check the reservoir level, water temperature, tower position and general plant condition before changing nutrient strength.
Helpful next steps
Once summer temperatures start climbing, a few small changes can make growing considerably easier. These guides will help you keep the rest of the system steady too.
Hydroponic Tower Maintenance
Learn how to keep your tower, reservoir and growing system clean and working well.
Understand pH and EC
Learn what your reservoir readings mean, why they matter and when they're useful.
Growing Through the Seasons in NZ
See how light, temperature and growing conditions change through the year.
Summer growing, made a little easier
You don't need to control every degree or chase perfect growing conditions.
Pay attention to what the weather is doing, protect the reservoir from unnecessary heat and make small adjustments when your tower needs them.
Sometimes that's moving it into a better position. Sometimes it's topping up the water.
And sometimes it's a tea towel and something borrowed from the chilly bin.
That's home growing.
