While Congress passed a sweeping economic recovery package last month that promised payments of up to $1,200 to most American adults, it remains unclear when the funds will arrive.

Adding to the problem, school closings across the country mean that many families who relied on free or subsidized school breakfasts and lunches to keep their children fed are facing even greater need.

A nearly tenfold rise in food cost

At exactly the moment that more Americans find themselves turning to food charities, the charities are facing shortages of their own. They rely on a volunteer labor force, one that skews heavily toward retirees. Across the country, older volunteers are sheltering at home for their own health and safety — sometimes by choice, and sometimes at the government’s direction.

Perhaps more alarmingly, many of the organizations that typically donate large volumes of food have themselves shut down. Restaurants, hotels and casinos have closed across the country. And grocery stores, which ordinarily share unsold inventory that is approaching its best-by date, have less to donate because their worried customers have been stripping so many shelves bare.

“When Americans began stocking up on toilet paper, pasta, dried beans and anything else they could get their hands on, supermarkets no longer had that excess, nor the time, to do the kind of shelf sweeps to check what they could give,” said Janet Poppendieck, an expert on poverty and food assistance. She is also the author of “Sweet Charity? Emergency Food and the End of Entitlement.”

The result is that food banks are buying what they used to receive for nothing.

At Food Bank for the Heartland in Omaha, the amount of food donated for March dropped by nearly half. The food bank typically purchases $73,000 of food in a month this time of year but has spent $675,000 in the past four weeks.