PHOENIX — Hussein Al Hamka is going to farm his famous cucumbers on a 15-acre vacant lot in the heart of this city, where nearly half of all lots sit empty and unused.

If his piece of fertilized dirt had a price tag, it would cost much more than he could ever dream of affording; the lot is valued at $25 million, or at least it was before the housing market collapsed and it was left undeveloped. To survive, Mr. Hamka, 50, an Iraqi refugee three years into his life in the United States, grows and sells cucumbers just like the ones he ate in his home country.

On Friday, Fidele Komezusenge, 25, a refugee from the Democratic Republic of Congo, picked rocks from the loose soil in the raised beds next to Mr. Hamka’s. Mr. Komezusenge was planning to plant carrot and cabbage seeds, his first farming foray since arriving in the United States in June. Nearby, Safala Chhetri, 50, a refugee from Bhutan who arrived in 2009, wavered between planting spinach or kale, but then decided to give onions a second chance.