Night watering???

[yager]

True or false you should not water your cacti at nightime? I read somewhere that the morning was the best time. Does it really matter?

[BobbyZ]

In my county in Florida we are still on water rationing cycle with timed irrigation mostly for lawns, however my scheduling also reflects the species. I choose to start watering early in the summer before sunrise with my roses, agaves and palms completed before 7 AM. My two cacti / succulent beds and potted specimens get less water and finish before 8 AM. The logic is that the water will go deeper in the soil with less evaporation, any residual on foliage will dry quickly and mionimize conducive environment for disease. In night watering the dew can stay on plantsin throughout the nightr and encourage fungal and bacterial diseases. In the winter my irrigation scheduling is once every two weeks and the duration in 50% of summer for a given area. Bobby Z

[CoronaCactus]

False, you can water day or night. Yes, it's best either early morning or just before/after sunset. As long as they get water they'll be fine. However, do not water at the peak of the day (11am to 3pm) when it's full blazing sun. You run the risk of scorching. If it's overcast, water away!

[Peterthecactusguy]

I set my irrigation system for my trees to go off at 4:30am for one and 5:30am for the other. For my cacti I water them in day light mostly usually around either 10:30am or maybe a little later but I avoid the noon-2 PM sun as it's VERY strong here.

[sundanz]

I water once week in my GH, in the morning before 8 am. It's very hot here right now.
Karin

[iann]

Some people overthink things, others are just obsessive-compulsives. I water when it rains, preferably a nice big thunderstorm

[DaveW]

Really depends on your climate. In hot dry countries watering in the evening allows the plants to take up water all night, whereas watering at the start of the day means more and quicker evaporation when the sun gets up, so less time for the plants to imbibe. In cold countries like the UK, unless it is a hot spell, it may be best to water early morning to ensure the plants initially dry out quicker when the sun gets up. In arid hot countries the reverse may be better, particularly if water conservation is an issue. In any case nature does not bother with such niceties, it just buckets down on them when it feels like it!

Never subscribed to the water drop scorch theory since it often rains on plants in habitat and within a short time they are subject to full sun again with drops still on them. The theory about water drops acting as lenses I think is a gardeners myth for the simple reason as soon as the area beneath the drops starts to heat up convection with evaporative cooling by the water drop would occur and as the drop evaporates it's function as a lens would disappear anyway. A more plausible theory is it is salts burn caused by concentrated chemicals left when the drop evaporates which you may get less with rain water but not tap water, or even more so if you use fertiliser, insecticides etc in your water.

Anyway an easy thing to prove or disprove, just put some water drops on the back of your hand and hold it in the sun and see if you get burnt below the water drops acting as lenses.

[CactusFanDan]

Never subscribed to the water drop scorch theory since it often rains on plants in habitat and within a short time they are subject to full sun again with drops still on them. The theory about water drops acting as lenses I think is a gardeners myth for the simple reason as soon as the area beneath the drops starts to heat up convection with evaporative cooling by the water drop would occur and as the drop evaporates it's function as a lens would disappear anyway. A more plausible theory is it is salts burn caused by concentrated chemicals left when the drop evaporates which you may get less with rain water but not tap water, or even more so if you use fertiliser, insecticides etc in your water.

Could droplets focusing enough light cause some kind of sun-bleaching effect, by the very intense light degrading chlorophyll? It'd probably have to stay for a long time, but I think it's possible. As you say, it can't be heat that'd cause a burn, but light can still cause damage.

As for when I water? Whenever I feel like it and whenever the plants want it. Usually in the day time.

[Rod Smith]

Never subscribed to the water drop scorch theory since it often rains on plants in habitat and within a short time they are subject to full sun again with drops still on them. The theory about water drops acting as lenses I think is a gardeners myth for the simple reason as soon as the area beneath the drops starts to heat up convection with evaporative cooling by the water drop would occur and as the drop evaporates it's function as a lens would disappear anyway. A more plausible theory is it is salts burn caused by concentrated chemicals left when the drop evaporates which you may get less with rain water but not tap water, or even more so if you use fertiliser, insecticides etc in your water.

Could droplets focusing enough light cause some kind of sun-bleaching effect, by the very intense light degrading chlorophyll? It'd probably have to stay for a long time, but I think it's possible. As you say, it can't be heat that'd cause a burn, but light can still cause damage.

As for when I water? Whenever I feel like it and whenever the plants want it. Usually in the day time.

I read an article in the paper last year that completely disproves the theory about water on leaves etc causing damage in the sun. Apparently a scientific trial was made which showed that no damage is caused and there is no "lens magnification" effect because the water droplets are never the shape of a magnifying lens. I had always thought the theory was a load of nonsense as I have never seen any plant in the wild or in my garden that has been damaged by sunshine after a rain shower. I often water my cacti from above in the daytime and have never seen any damage either.

[Kada]

I only water at night, mostly to avoid the heat for myself. Standing in a greenhouse in the sun for any amount of time just seems crazy.

[Rod Smith]

I only water at night, mostly to avoid the heat for myself. Standing in a greenhouse in the sun for any amount of time just seems crazy.

With the weather we've had this year, the temperature in the greenhouse at midday is just about right - low to mid 20's Centigrade.

[iann]

I read an article in the paper last year that completely disproves the theory about water on leaves etc causing damage in the sun.

In the paper you say? Then it must be true

For a more sensible assessment, try actual scientific papers, not tabloid headlines propagating urban anti-myths. For example:
http://onlinelibrary.wiley.com/doi/10.1 ... 150.x/full" onclick="window.open(this.href);return false;

[DaveW]

Seems to be what I said, that the area under a water drop would not burn due to convection currents within the water drop and evaporative cooling until the drop itself disappeared. Only if the drop was held up off the surface by hairs could burn directly underneath occur:-

"By contrast, sunlit water drops, ranging from spheroid to flat lens-shaped, on horizontal hairless leaves of Ginkgo biloba and Acer platanoides did not cause burn damage. However, we showed that highly refractive spheroid water drops held ‘in focus’ by hydrophobic wax hairs on leaves of Salvinia natans (floating fern) can indeed cause sunburn because of the extremely high light intensity in the focal regions, and the loss of water cooling as a result of the lack of intimate contact between drops and the leaf tissue."

What they did find was burning could occur obliquely away from the base area of the drop itself if watered early in the morning or later in the evening when the sun was low, rather than the middle of the day when it was high and focused on the area under the drop itself, the very time the old gardeners recommended watering to avoid burning!:-

"We found that a spheroid drop at solar elevation angle θ ≈ 23°, corresponding to early morning or late afternoon, produces a maximum intensity of focused sunlight on the leaf outside the drop’s imprint. Our experiments demonstrated that sunlit glass spheres placed on horizontal smooth Acer platanoides (maple) leaves can cause serious leaf burn on sunny summer days."

[tudedude]

Cactus spines seem perfect for holding droplets off the surface. I guess the safest is to water around the base of the plant, at night, during a new moon, 3 hours before sunrise, with a cup of coffee.

[Rod Smith]

I read an article in the paper last year that completely disproves the theory about water on leaves etc causing damage in the sun.

In the paper you say? Then it must be true

Yes, Ian - if only it were so.