Wheat gained ground after closing lower on Tuesday with short-covering by funds expected support prices.
The most-active corn contract on the Chicago Board of Trade had risen 0.3pc to $3.95-1/4 a bushel by 0224 GMT, after hitting a one-year high on Tuesday.
Wheat added 0.2pc to $4.79-3/4 a bushel and soybeans were up 0.6pc at $8.27-1/4 a bushel.
"Weather forecasters now have the US corn-planting window coming to an end with farmers struggling to plant," said Tobin Gorey, director of agricultural strategy at Commonwealth Bank of Australia. "Combined with a big investor short, the market is galloping higher."
The US Department of Agriculture said a lower-than-expected 49pc of the US corn crop has been planted, the slowest pace on record, based on data going back to 1980.
Soybeans were 19pc planted, also short of market expectations.
The wheat market is being supported by short-covering by funds although ample world supplies are likely to keep a lid on the market.
Top exporters, led by Russia are forecast to harvest bumper crops in the coming months.
Soybean prices were pressured on expectations the USDA may soon announce a trade-war aid package for farmers that could boost soybean plantings and possibly further swell record-large stocks of the oilseed.
Commodity funds were net buyers of CBOT corn and wheat futures contracts on Tuesday and net sellers of soybeans, soymeal and soyoil, traders said.
Estimates for wheat ranged from funds buying a net 4,000 contracts to selling a net 2,000 contracts.