Watering at night or early morning -- does it matter?

[iann]

The water in the pot of a cactus should last long enough (ie days, not hours) that it shouldn't be a factor in when you water. Certainly if the next night is going to be so cold that you don't want a plant to be in wet soil then you shouldn't be watering at all, because the soil will still be wet after 12 hours (and if not then it should be!). Warm days and cool nights are just not a big problem though. 40F night, not an issue. 40F night followed by 40F day, not good, but you can probably still get away with it in dry sunny Arizona. Dangerous in cloudy humid England.

[Jumbie]

I read the first page of replies and nobody has mentioned that cacti are CAM (Crassulacean Acid Metabolism) plants.

This is something I hadn’t heard of until somewhat recently. As I understand it, and please correct me if I’m wrong, plants that are considered CAM prevent water from being lost to perspiration by closing the stomata during the daytime. At night the stomata opens to intake CO2 and exchange for oxygen. Because most of water/nutrient is up-taken via transpiration (when stomata is open) this happens at night.

I’m explaining this as it was explained to me. If i have it all wrong, I hope someone corrects me. I do not claim to be an expert and just wanted to bring this up:
A/so anyone who understands it better than me can correct my explanation
B/in case I do have it right and this happens to help anyone with their plans

I will say I’ve been watering in the evening and my plants are doing very well.

[Nino_G]

You understand CAM correctly. Most important adaptation of CAM plants is capability to "store" CO2 that plants take during the night to be used during the day in a process of photosynthesis. Rather complex chemistry of that process is well explained here: https://www.sciencedirect.com/topics/bi ... metabolism

[greenknight]

Correct - except that young cactus seedlings don't use CAM photosynthesis. Not something you need to worry about, just keep them evenly moist all the time and they'll be happy.

I usually water my adult cacti in late afternoon, because I'm not a morning person and there's no sense in standing out in the mid-day sun doing it. As ian said, it's really not important what time of day you do it.

[keith]

If you spray a pesticide you should probably water in the evening or on a cloudy day

[Steve Johnson]

That's an old thread I started, and it seems like a silly question I asked back then. With 12 years of experience under my belt (so to speak), I'll answer my own question...

Although it doesn't matter if we water at night or in the morning, IMO watering at night is better because it maximizes the amount of time cacti and succulents have for taking up water and nutrients in the growing season.

If you spray a pesticide you should probably water in the evening or on a cloudy day

Jumbie and Nino_G make a good point about CAM, something I didn't even know about when I started the thread. Based on what I learned since then, I'll refine what Keith said by stating that pesticides sprays should be applied, but only at night for a couple of reasons:

• This avoids the potential for phototoxicity problems that may occur if we're spraying while plants are getting sunlight. Spraying while they get direct sunlight is just asking for trouble.

• The most effective pesticide sprays are transdermal -- the active ingredients literally getting under the skin of cacti and succulents. 3 examples are:
  • Imidacloprid working against mealies and armored scale.
  • Avid and TetraSan miticides working against spider mites and flat mites.

Spray at night while the skin pores (stomata) are open to receive the maximum transdermal effect. From what I've seen, the benefits of transdermal sprays last for about 30 days.

[DaveW]

A lot can depend on your climate. In a hot climate watering at night may mean the pot stays wet for longer, which may be desirable. Whereas in a colder climate watering in the warmth of the day will allow it to dry out quicker than at watering at night. The question is how long is too long for our plants to stand in wet soil? Again the porosity of the soil in the pot and how fast it dries is another variable. As usual it comes down to whatever works for you!