Healthy potato leaves above ground do not tell you whether developing tubers remain covered below. Rain, watering and growth can leave the surface uneven. Earthing up is the practice of drawing suitable soil or compost around the growing stems to maintain coverage.
The RHS potato-growing guide explains that this helps protect developing tubers from light, which can cause greening, and can protect early shoots from frost. Its seasonal advice is written for UK conditions; planting and maintenance timing need to fit your own climate and growing method.
Work around the plant without excavating it
Follow guidance appropriate to the variety and bed or container. Bring material around the stems gently rather than digging into the root zone to search for potatoes. Leave the growing plant with the foliage it needs according to the recommended method, and avoid compacting the mound through repeated foot traffic.
After heavy rain or watering, look for washed-away areas or exposed tubers. Restore appropriate coverage promptly. Covering an already green potato does not establish that it has become safe to eat; discard green tubers rather than treating soil as a way to reverse the problem.
Give containers room for the same job
If growing in a bag or pot, plan the filling stages before planting and use a container with suitable drainage. A container filled to the rim at the start leaves little room for later additions. Follow a reliable container-growing method rather than assuming that every extra layer will produce another large tier of potatoes.
For a simple growing record, note the variety, planting date, earthing-up dates and any coverage lost after rain. At harvest, record the condition of the tubers as well as the amount. Those observations can help you adjust the method next season without attributing every difference to mound height.
Keep crop protection, watering and harvest timing in the wider plan. Earthing up addresses a particular need; it does not replace checking for disease or keeping the growing medium in suitable condition. The immediate aim is steady growth with developing tubers protected from light.