I know that obvious high temps will cook plants, but my personal gardening experience is pretty limited—other than eating the products. Anyway. . .
I heard this exchange recently, and wondered if there how factual it was, that you should run out the warm water (assuming your garden hose has been sitting in the sun) before watering your plants. I see various gardening sites that talk about the effects mainly of cold water, less on warm water—but in either case, nothing showing any scientific factual results. Is this just some more gardening folk wisdom? Does it matter?
I have always let hot water run out of the hose before using it to water plants (interestingly, this hot water hasn’t caused any obvious scorching of lawn grass where I’ve run it out, but then again grass may be tougher than ornamental plants).
In general you want the water to be reasonably close to the ambient temperature when you water. In my book that means no unpleasantly hot to the touch water or ice water (weirdly, they sell potted orchids in supermarkets with the instruction to water by placing ice cubes in the pots, which sounds nuts to me).
I don’t know of any studies offhand where this subject was researched, but maybe some bored graduate students published papers in the Journal of Applied Horticulture or suchlike.
I can imagine that a black hose left out in the sun in the southern parts of the US could get scalding hot inside. Might be good to let it run cold before any people touch it, let alone plants.
But if it’s merely warm? I don’t see that hurting plants.
I can make an edumacated guess why one might water orchids by putting an ice cube in the pot.
Many orchids are epiphytes, which means they grow on the surface of other plants (typically rain forest trees and such). Their “roots” basically just cling to branches that they grow on, rather than digging in. Terrestrial orchids grow in the ground, but typically in very loamy soil that won’t hold much water very long. Orchids still get all the water they need, living in tropical rain forests.
If you water a potted orchid, all the water will just immediately run right through and drain off. But by putting an ice cube there and letting it melt slowly, you would effectively have a long-lasting slow-drip watering system.
Luckily, even in this part of the world where the only thing separating us from Hell is a screen door, garden hose temps usually fall somewhat short of this.
Oh, you have that too? I planted morning glory seeds at a new (to me) rental home, so I left all these seedlings to come up, thinking I’d had some kind of Jack’s beanstalk type of luck with the seed packet. They interbred, so subsequent generations of morning glory were unusually hardy!
Boiling hot water might kill some of the bindweed root system, after it kills everything else in the area. Worth a try, though, since the effects don’t persist like herbicides would, so you can replant after you literally go with the scorched-earth policy.
OP, I could see hose water temperature being most relevant in early spring – seeds germinate and seedlings grow partially in response to temps, so irrigating with warmer-than-ambient-air water might speed up that timeline artificially. Watering with colder-than-ambient-air water in the heat of summer might buy a little time for plants that wilt in the heat regardless of moisture levels, too.
I think the ice cube in the orchid is to prevent people from over-watering them. Just one cube is an easy pre-measured amount of water that is about all the orchid needs.
