Looks like the irrigation season is upon us. My yard hasn’t been rained on in over a month now. As you start to water your plants for maximum yield and efficiency you might wonder, as I often have, what time of day is best: morning, afternoon, evening, middle of the night?

Whenever you can be watching — that’s my operating principle.

When I say this I’m thinking of what time of day it’s best to run an irrigation system, like a set of drip lines in a vegetable garden or mini-sprinklers under fruit trees. And what I mean is that it’s best to run that system at a time when you are usually home and able to observe. For example, if you leave for work every day at 6 a.m., then it’s best to run your irrigation at maybe 5 p.m. when you’re home from work, not at 7 a.m. while you’re gone even though both 7 a.m. and 5 p.m. are perfectly fine times of day to water plants.

I think that being able to watch your irrigation system run is vital because of all of the things I’ve noticed over the years while watching my systems operate. I’ve noticed clogged drip emitters, mini-sprinklers that needed a flick to get them spinning again, a leak in a valve, a drip emitter that I forgot to plug up after the plant it was watering died, and on and on.

My system was running just the other day when I heard a curious spraying sound. I dug to find this:

Irrigation leak

If you’re around to watch while your system is running, then you can catch these things red-handed rather than read the evidence of a dried-up plant or a mossy spot in the soil after the problem has been long occurring out of sight.

If you’re watering by hand using a hose or sprinkler or watering can, then of course you’re going to be watching, so is there a best time of day for that? Morning and evening are both great there too. I’d say that only noon in the middle of summer is not ideal, and that’s because you’re going to lose a little more water to evaporation at that time. But who would choose to stand in the sun in the middle of the day in summer anyway?

One thing we don’t need to worry about here in Southern California is the idea that watering in the evening or at night and wetting the leaves of plants might encourage fungal diseases. That might be a consideration in more humid climates, but it’s a non-issue here. I’ve watered and wet leaves in the evening some years and never wet leaves other years, and I’ve seen no difference in the incidence of diseases like powdery mildew and downy mildew — and that’s both in my gardens near the ocean and in the relatively drier inland areas. My observations have been that mildew hits plants like peas and squash as they age regardless of the watering regimen, and the occurrence of botrytis on blackberries is mostly due to insufficient sunlight, not wet foliage and berries.

mini-sprinkler under avocado tree

What do I currently do in my yard? I run mini-sprinklers under my fruit trees in the late afternoon, usually starting around 4 p.m. I like this time because the common west-northwest breeze coming from the ocean is starting to slow down, but it’s still not totally calm; having some movement in the air helps distribute the sprinklers’ droplets a little more broadly.

And I run drip lines in my vegetable garden in the morning around 7 a.m. This is because I’m often at home at this time, and I can “walk the lines” briefly to check on them.

When can you be watching? That time is the best time for you to water your plants, in terms of their health and the efficiency of your water use in the long run.