Maybe some of you can help me out. Years ago i stumbled across an article referring to an experiment (scientific or home based I can't remember) regarding irrigation timing. I think it was done with container gardening. The debate was whether the only benefit to watering outside of peak sunlight/heat hours was that less water was lost to evaporation and that you could actually increase yeild and plant vigor with less water by irrigating during the heat of the day and that negated any benefit of water conservation by watering in the late evening or early morning hours. I can't find this now. Anybody......
Another factor: if you wish to avoid fungal problems, water early in the morning because there will already be morning dew followed by a day of dry sun to dry out the soil surface and, thus, avoid fungal issues. If you water in the afternoon or evening, the soil won't dry out as much and will remain damp throughout the night - thus enticing fungal issues.
Thats a good point paul. This always comes up this time of year when I hear suggestions from varying sources to water in the evening. I think it is one of those things that gets repeated over and over and few people stop to wonder if it has any merit. Sort of like the advice to drink a gazzillion ounces of water every day. It pays to run everything through your baloney checker thats for sure.
watering in the heat of day can actually injure plants. I've heard that it's a shock, and then also I've experienced that wilty lettuce leaves etc. are just much more prone to damage in their weakened state.
If I see the wilt, don't freak out, and then water later when it's cooler, the plants will be just fine. I aim for morning but have been known to lapse and do evening, though it's not my ideal.
I've also heard that watering lettuces, spinach, etc in the morning helps to keep them cool so that they're less likely to bolt.