The gains came after the most actively traded corn contract earlier in the session dropped to its lowest price in more than three months and after soybeans fell to their lowest in more than two months.
Question marks surround the upcoming harvests of both crops after historic rains and flooding stalled plantings this spring. The delays left fields more at risk to damage from potential frosts.
"People are starting to realize we've taken these things down pretty far pretty fast," Jim Gerlach, president of broker A/C Trading in Indiana, said about market prices.
"This crop is not in the bin by a long stretch."
The most-active corn contract on the Chicago Board Of Trade was up 1.5pc at $3.71-3/4 a bushel at 12 p.m. CDT (1700 GMT). The most-active CBOT soybean contract rose 0.8pc to $8.65-3/4 a bushel.
The markets are going to concentrate on the risk of frost for the next six weeks and react to forecasts that reach out into late September and early October, said Tomm Pfitzenmaier, analyst for Summit Commodity Brokerage in Iowa.
"The soybean crop size really depends on the fall and the timing of the first damaging frost," he said.
Soybean traders also are watching developments in the ongoing trade war between the US and China, the world's biggest importer of the oilseed.
China slashed purchases from the United States after imposing retaliatory tariffs on imports of American soy last year, in response to US duties on Chinese goods.
The US Trade Representative's office on Wednesday reaffirmed President Donald Trump's plans to impose an additional 5pc tariff on a list of $300 billion of Chinese imports starting on Sept. 1 and Dec. 15.
In wheat, the most-active CBOT contract was down 0.5pc at $4.74-1/2 a bushel.
Dealers said French prices had fallen to a level where they could compete with supplies from the Black Sea region.
Egypt's state grains buyer, the General Authority for Supply Commodities, said it bought 350,000 tonnes of Russian, Ukrainian and French wheat on Tuesday at an international purchase tender. No US wheat was offered.