JMoney wrote:

I would disagree with using warm water, unless it's at or below 70 degrees F. Anything above that, and you are asking for root shock, and root problems. High temperature waters promote not only shock, but root Pythium and harmful pathogens.

Not I wrote luke-warm. Not hot. As long as you can keep your hand in in the water without havinh the feeling it is hot, you should be OK. I have been watering my plants wath warm water for over 20 years and never had problems, except for the soil staying wet fairly long due to enourmous water absorption.

m5eaygeoff wrote:

Warm water is a novel idea, I won't be using it that's for certain.

It is not new, but merely something you have not heard before (...). I used to grow succuluents (Cacti etc). Here it is quite normal to use warm water after winter. Succulents need a cold phase during which they are left to dry out almost completely over the course of winter. When they are brought out of winter storage, and are brought back to growth by increasing humindity of the air, the first watering should be done with hand/luke warm water to ensure the whole pot gets re-wetted.

The reason it works is because of physics. Water has fairly high cohesive bonds (Water likes to stick with water, which causes the droplets on certain surfaces). Dried out soil is actually hydrofiel (It rejects water). When you lower the strength of cohesive bonds, water alsolikes to connect to other surfaces => It connects better with the soil and can overcome the hydrofile properties of the dried out soil a lot easier.

Furthermore, the roots prefer warm soil over cold; They just function better. If you water with cold water, your roots get a shock. Warm water supprots the roots (Hence the heating mats underneath growing bed and seed trays: They avoid the roots getting to cold and start being infected by fungi).

Plants should rarely be watered anything but water between 68 and 70F water. The only exemption to this is if for example you are growing outside and a frost is coming and you get up at 2am to water 90F water on your root zone to avoid frost damage (since frost damage comes from the freezing of roots, not the leaves) but this also brings a shock to the plants, just less of one than being froze. It's all about saving the crop, and the lesser of the evils. Just because plants are given water outside of a 68-70F range, and you are not visually seeing any effects from it, does not mean they are not effected. That range of water is to keep, as I said before pathogens, and root issues down, but also to promote optimum growth. You may think, well I grow great big plants, well think how much bigger and healthier they would be in ideal conditions every day all day through an entire growing season?