Others require consistently moist soil. Next, judge the situation where it will be growing. Sandy soils have very little capacity to hold moisture and dry out quickly between waterings. Soils with lots of organic matter have good moisture retention. Clay soils have good moisture retention but may hold too much water.
Sloped soil drains much more quickly.
You will also need to judge the plant's general condition. A healthy plant with an established root system will be much less demanding than one that is newly planted or one that is already struggling. Taking into account everything you know about the plant you are growing and the site, you can then rely on outward signs. Water Ideally, nature would provide enough slow, evenly spaced rains to meet your plants' water needs. But in reality, you will probably have to supplement nature for part of the season, especially for new plants.