Water stains, or water on leaves burns when exposed to strong sunlight. Iron may be needed, or you may be watering too much. Might be bugs chewing on it too. Spray with Neem. Miracle Grow is way too harsh for most potted plants. Its raw salts and is pure chemicals. The end result is weak or sickly herbs, with bad taste. I never use any chemical fertilizers. A good ORGANIC HERB fertilizer is from Gardens Alive.

Here is a link that might be useful: ORGANIC herbs fertilizer

Here in the subtropics, my plants are exposed to truly fierce full sun, and in summer a tropical storm can hit at any time during the day. I've never, ever, had any leaf-burning result of water on leaves in the heat. Nor sunburn on basil, which can take as much heat as you can throw at it (via the sun!).

It is possible, however, to burn a plant by using too much fertiliser. I suggest you use a slow-release fertiliser, or better still, a handful of compost from time to time, or even spray the plant with some diluted worm wee.

If you suspect bugs, spray with some garlic spray.

Perhaps I should have made myself clear. Prior to yesterday, I had never fertilized the herbs, just watered when needed (soil dry) and left it in the sun. I thought maybe the herbs were lacking some nutrients and got the fertilizer. 1/2 tsp per gallon was used.

The leaves have not gotten wet in the sun, I water around the edge of the pot, not at the base of the plant, so nothing but soil gets wet.

Perhaps I will try the organic fertilizer.

The Miracle Grow only contains the basic chemicals of urea, phosphorous, and potassium. All plants need many nutrients, things like iron, calcium, zinc, magnesium, copper, and others are also necessary. I grow a decent sized garden and never add chemicals of any kind. Besides giving plants that produce edibles an odd taste, they dissolve quickly and don't provide long term nutrients that all plants need. Urea, for instance breaks down within a few days of application and can reach root damaging levels very quickly, which can cause plants to produce more greens, but at the expense of taste and health. Most organic based ferts are slow release. Your plant may also need repotting into a larger pot. Many herbs don't do as well in pots, especially if they are cramped.

My poor fig tree wilts every day, and I have to add at least a gallon of water per day. The pot is 2'x2' square and 2 feet deep. Its roots are massive and show up on the surface of the soil now. I have to plant it in the garden as its just getting to big to deal with. If I miss a single day of watering, the unripe figs will drop off quickly. Right now, older leaves are yellowing and its acting like most fall trees that see cool nights and cooler days. Soon it will drop off all its leaves, but I hope to get a few more ripe figs before then. After pouring in a gallon of water, I don't even see any dripping out the drain holes at the bottom, so I know its soaking up water like a dry sponge.