Cold Management in Nutrient Reservoirs/Tents

Brrr...Its getting cold!

Generally in Queensland, cold doesnt bother the hydroponic grower; this year (2022) has been quite different, as it is getting hotter in the summer months and colder in the winter months. Sometimes, its hard to know just HOW cold your plants can get without them suffering. Here we have a conversation between Scott and a grower discussing methods of conserving/creating heat for reservoirs, and also for the tent itself!

Grower:

G'day scott! My system is all up and running! However, Winter has come and it seems as though my plants are slowing down? Could you suggest any way to keep my water temp higher for these colder months? The res I am looking to heat is a 50L container and my tent size is 1.5m x 1.5m.

Scott:

Water heaters, if indoors, usually work off of 50 Litres = 50Watt heater - but since you are a bit cold I would go up to a 100W heater which will work half as hard.

https://www.hydrocentre.com.au/index.php/other/heaters-for-water.html

To make the heater more efficient - use some sort of insulating material under/wrapped around your tank, think Polystyrene or some old towels! I have seen some aluminium foil tanks that are very spacey!

Some growers have used cheap eskies as tanks! - which is a 'cool idea' - see what I did there - but at least keeping a lid on the tank will help to prevent heat escaping too fast.

If heating outdoors you need a tank that is insulated or just give up heating at night.

For air heating, most people use a source of intake air that is air-conditioned if available. Fan heaters do a quick efficient job - but the thermostats are not always great, and blowing the hot air on a plant can cook them, so redirect the fan heaters away from the plants. Perhaps up near the roof near a fan and away from the plants. There is also a lot of heaters such as ceramic heaters and so on that are available that will work in a similar way.

So the lowdown on heat:

Nutrients have to be soluble in the root zone, but also within the plant.

1. Below 18 degrees the solubility of phosphorus starts to reduce

This is why the first sign of cold is a phosphorus deficiency. My best clue for that is stems going more purple than normal.

2. below 15 degrees most of the other elements start to do the same.

You only have to keep nutrients above 18 degrees about 75% of the time.

However, if you heat the water but the plant is cold the nutrients won't be mobile in the plant because they are not warm enough to move around properly.

So keeping the plant temperature above 18 degrees is important. Heating the roots with warm nutrients is fine. 

Growing media will retain some heat between feeding.

This heat should radiate upwards into the plant. 

If a plant stops transpiring moisture through its leaves it stops growing/taking up food and water.

If is not transpiring (read perspiring) because it's so cold, then we need to heat up the air so they do so.

There are also some experiments done with Infrared lamps to heat the plant, but the chances of cooking the plant is higher.

In the end, you can decide whether you want the plants to grow as normal, or slow down a bit in the cold weather.

If the slowdown is acceptable, then down to 10 degrees for 5 hours a day wouldn't bother me or the plant much.

Keep an eye on the plant for signs they aren't happy though. 

And use one of our maximum/minimum memory thermometer hygrometers to find out what happened overnight.

Hope that helps

~Scott