"Brand into your memory, an image of the healthy, well-grown plant".This advice has served me well and I commend it to you. Observe the plant(s) carefully and remember the angle of the leaves to the stem, how the leaf blade itself is held by the midrib and the very tip of the main stem. When moisture stress hits the plant, some cells start to shut down and tissues go limp; the plant wilts. The growing point flops to one side or the other, the leaf blades droop downward from midrib and the whole leaf does the same at its attachment to the stem You can observe this in the heat of the day and if the plant regains its turgidity later on, it is not a problem. As the stress increases, the plant will take a longer time to recover. That will be your cue for watering. It is not difficult but the process has to be learned and in a short time you will be saying "that third basil from the end needs some water". And people will wonder how you can tell. Please bear with me for one more thought. There is a lot of tension underground. The soil particles will refuse to give up moisture at some point. As that point approaches, the plant has to exert more and more of its own energy to extract moisture for it to live. There will come a point when it has no energy to do anything else. Too much water will deprive the roots of oxygen and the roots and the plant will DROWN! So if we want to have well grown plants that give meaning to words like luxuriant and luscious, we must manage watering skillfully.