I have a mint plant outdoors in a pot that grew rapidly and then suffered from some insect which just loved eating it. It's in a mostly sunny spot next to a high bed. I sprayed it with a solution of water, liquid soap and canola oil. But later, it looks like the leaves are burnt--not always from the edges but from spots in the middle as well. Could this be the canola oil in the spray? Also wondering if it could be something else.
I let the new growth grow without spraying, but it seems to be affecting new young leaves as well. They turn black and are almost crispy.
just general advice - not sure what would be eating your mints leaves.
Mints in general like a water retentive moist soil.
Placing it in sun will make the oils that are attractive to us stronger, but it will need close attention to moisture levels to stay healthy.This may mean watering daily.
You state that it is in a pot so in sunny weather will dry quite quickly and the sun on the pot, if it is dark in colour will add to the heat affecting the roots. It may be that the plant is stressed which could reduce its ability to defend itself against predators. The spray ingredients may or may not have affected the plant. What may have 'burnt' the leaves could be spraying liquid onto the plants leaves in bright sunshine as the droplets act as lenses for sunlight and scorch the tissue on which they sit.
As mint are invasive, its good to keep them in a pot or container but it may be beneficial to sink/bury the pot in the ground. This will contain the mint, slow water loss and allow the mints roots to go through the bottom of the pot, if needs be, to get moisture. Planting amongst sun-tolerant/sun-loving plants will shade the mints roots and help keep them cool but whilst allowing its foliage to take advantage of the sun.