ING's local retail banking arm has hit a growth sweet spot after hauling in more than A$5 billion of new deposits during the 12 months to the end of March 2019.The remarkable growth trajectory of the Dutch-owned bank in Australia confirms it as the unrivalled challenger to the four major banks in domestic retail banking.Data published by APRA over the last year show that ING is now the fifth largest home lender and retail deposit taker in the country.ING grew its deposit base by 17 per cent to $34.5 billion in the year to the end of March, which means its retail liabilities equate to about one-third of the ANZ business.According to their prevailing rates of growth in the deposits market, ING is on track to surpass ANZ as the fourth largest deposit taker within the next decade.The bank's aggressive growth on the liability side of its balance sheet is almost matched by deepening lending activity.In the last 12 months ING has overtaken Bendigo Bank, Suncorp and Macquarie after increasing the size of its loan book by $7 billion to almost $60 billion.Most of the growth came through a 13 per cent surge in lending to owner-occupiers, although the bank recorded almost no growth in investment loans.ING also stepped up business lending.The bank swelled its business loan book by $2 billion or 25 per cent to $9.7 billion in the 12 months to the end of March.It appears to have stolen a march on other challenger brands such as Bendigo and Bank of Queensland that are each looking to rebuild SME lending volumes to support revenue growth as credit demand from homebuyers cools.