Measure the water, not just the weather
Put a suitable thermometer probe in the circulating reservoir, away from a sun-heated wall or the immediate cooling outlet. Check in the morning and again during the hottest part of the afternoon. In NFT channels or towers, check the returning solution too: a shaded tank can send water through very hot exposed pipework.
Record air temperature, solution temperature, water level, EC and pH. A few days of readings will tell you whether your changes work. A 43°C forecast is an air temperature, not a prediction that your reservoir will reach exactly 43°C.
What temperature should you aim for?
There is no single perfect setting for every crop. Colorado State’s PlantTalk root-health guidance recommends about 20–22°C (68–72°F). Use that as a starting reference alongside guidance for your particular crop, rather than treating it as a universal survival limit.
If your solution is climbing well above your crop’s normal range, act early. Warm water holds less dissolved oxygen, while roots still need oxygen to function. A temperature reading alone cannot diagnose root disease, and adding more bubbles does not remove the heat.
Start with shade: stop the heat getting in
Shade the reservoir, lid, exposed supply lines and return pipes, especially from afternoon sun. Use an opaque, covered reservoir to keep light out of the solution. A pale outer surface or shaded reflective cover can reduce solar heating; keep any cover clear of pumps, electrical equipment and ventilation openings.
For the plants, use temporary shade appropriate to the crop and your conditions, keeping space for airflow. Avoid a fixed shade percentage for every garden: lettuce and fruiting tomatoes have different light needs. A greenhouse needs ventilation as well as shade; a fan moving already-hot air is not refrigeration.
Insulate the reservoir—and watch the result
Insulate the tank and lid, and protect accessible pipes from direct sun. Insulation slows heat transfer; it does not actively cool water that is already hot. Keep the lid accessible for checks and leave equipment vents unobstructed.
A larger working volume usually changes temperature more slowly than a tiny bucket, but it can still heat up during a long spell. If relocating the reservoir to a cooler sheltered place, preserve the system’s intended flow and drainage. Do not bury a tank unless it is designed and installed for that purpose.
Underground storage: useful, with the right tank
Ground that stays cooler than the afternoon air can help buffer a reservoir against daily temperature swings. An underground reservoir is an option worth planning, especially for a permanent outdoor system. It is passive heat buffering, not a guarantee of a particular water temperature: local soil, depth, moisture and a prolonged heatwave all affect the result. Measure the ground temperature at the proposed depth before assuming it will provide the cooling you need.
Use a tank specifically rated for underground installation and compatible with nutrient solution. An ordinary tote, barrel or above-ground IBC can buckle under soil pressure; do not simply bury one. Follow the tank manufacturer’s instructions for excavation, bedding, backfill and anchoring where groundwater could cause flotation. Check buried services and local requirements before digging, and get qualified help where needed.
Keep a secure, accessible lid above flood entry points, provide drainage away from the access opening and prevent soil or stormwater entering the solution. You still need to inspect, clean and replace the tank or equipment. Do not enter a tank. Keep electrical equipment dry and accessible, and preserve reliable pump flow and system drainage. Shade or insulate exposed pipes too, because cooled water can warm again on its trip to the plants.
Keep oxygen and water moving
Check pump flow, filters, return lines and air stones before the heatwave. In deep-water or raft systems, reliable aeration matters because the roots sit in the solution. Keep an air pump in a shaded, ventilated position and follow its installation instructions.
Do not turn off an NFT pump just to reduce its heat: exposed roots can dry rapidly when flow stops. Reduce heat sources without interrupting essential irrigation. For a passive Kratky system, preserve the root air gap when topping up; do not refill to the brim and drown the established air roots.
Have a plan for a power failure. A battery air pump can support aeration in a small deep-water system, but it is not a replacement for an NFT circulation pump. Match your backup to the equipment the roots actually depend on.
Frozen bottles: a short-term helper
For a small reservoir, clean, tightly sealed bottles of frozen water can provide temporary cooling without adding meltwater to the nutrient mix. Keep them away from roots, pump intakes and sensors, and check the temperature as they melt. Inspect bottles for leaks and use containers suitable for repeated freezing.
Cool gradually rather than chasing a sudden ice-cold reading. This is a practical stopgap, not a proven all-day solution for 43°C weather. A big tank may need repeated swaps and more cooling than bottles can supply. Loose ice adds water and changes the concentration; do not use it as an unmeasured routine fix.
When a water chiller makes sense
If shade and insulation cannot keep the solution within the crop’s suitable range, consider a purpose-built water chiller. Choose equipment compatible with nutrient solution and size it for the actual reservoir, flow and heat load at your expected outdoor temperature. Ask the supplier about capacity during extreme heat; a tank-volume label alone is not enough.
A chiller releases heat where it operates, so place it with the ventilation and clearances its manufacturer requires. Follow local electrical requirements around water. Set a crop-appropriate temperature and monitor the reservoir, rather than assuming the chiller display represents every root zone. Compare running costs before buying.
Top up using readings, not guesswork
Hot weather can change water use and nutrient concentration quickly. Check water level, EC and pH daily during extreme heat, following your crop and nutrient product guidance. Restore the intended water level with suitable water or correctly mixed solution according to the readings, allow it to circulate, then measure again.
Do not automatically add full-strength fertilizer at every top-up, or halve the feed because it is hot. Both can move the solution away from what the plants need. Keep the nutrient containers and stored top-up water shaded. Use water of suitable quality and a reasonable temperature; an abrupt large cold-water replacement is not the aim.
Watch the roots as well as the leaves
Wilting can come from heat, interrupted flow or root problems. Check the equipment and solution before adding more fertilizer. Look for a change in root texture, unusual smell or worsening plant condition. Root colour alone is inconclusive because some feeds stain roots.
Cooling and aeration support root health, but they do not cure an established infection. If symptoms persist, seek local horticultural or diagnostic advice. Avoid adding household peroxide, bleach or other treatments to a planted reservoir by guesswork.
A simple heatwave checklist
Before the hot days arrive, shade and insulate the reservoir, check the thermometer and meters, clean blocked flow paths and prepare a realistic cooling and power-backup plan. During the heat, take morning and afternoon readings and check the plants at the hottest time.
At 43°C, survival may take priority over maximum growth. Even with cooled roots, lettuce can struggle and fruiting crops can have heat-related flowering problems. Use crop-appropriate shade, consider harvesting ready crops early, and delay vulnerable new transplants until conditions ease. No cooling trick guarantees a crop through extreme heat.
- Morning: check level, temperature, flow, EC and pH.
- Afternoon: recheck temperature and returning solution; inspect plants and cooling equipment.
- Evening: record the day’s high reading and prepare the next day’s bottles or cooling plan.
Keep growing—and keep comparing notes
You do not need to start with the most expensive equipment. Start with a thermometer, shade and a reliable system, then let the readings guide the next step. I would love to hear what Australian growers are using and which changes make a measurable difference. We can build on this guide with real experiences, without promising that one setup suits every climate.