And I have no intention of being cheeky with this......as often as necessary! Truly, it is impossible to tell anyone how much or how often to water. There are far too many variables involved that just do not translate over the Internet.

You do not want the plants or the soil to dry excessively. Neither do you want the soil to remain excessively wet. The slope, possible lack of water penetration due to clay soil and also sunlight would indicate more frequent watering required than would be on a flat, looser, lighter soil and more shady situation. Weather will also play a big factor. Frequent checking of both the plants and the soil conditions will be necessary through the summer and then water accordingly. You can start slacking off when temperatures begin to cool in fall and normal rainfall commences.

SOunds like you have found the perfect plant for that location. If you can spread some mulch it will keep the soil moist between rain or your watering. It has been my experience if this plant dries out it's not happy, so don't let the soil dry out if you can help it. Purchased mulch such as compost might be cheaper than replanting! I dislike bark mulch. You want something that doesn't form a tight mat that water can't penetrate. Used coffee grounds free from St*rbucks with a light layer of mulch over the top reduces cost.