The term has a rough, throaty quality to it that gives a good indication of the effort involved in howking something from the ground; a mere scraping of the earth falls short of conveying the effort involved.
Archaelogists howk for bones and ruins; miners go howking for coal; potatoes are howked out by farmers. All three jobs involve hard graft and long days spent excavating deep beneath the soil.
Potato howking was once common in Scotland; farmers employed schoolchildren in the October holidays to pick potatoes that were unearthed by a digger.
The use of howking can also be extended beyond hard labour. You could howk a secret from someone, or howk a jumper from a pile of laundry.