Gordon Johnson, Extension Vegetable & Fruit Specialist; gcjohn@udel.edu
The first early fresh market sweet corn plantings have been planted. This March planted corn most often is planted under vented clear plastic covers to provide for extra heat accumulation. This allows for harvest in June, several weeks ahead of field plantings. Another option to improve earliness is to seed through plastic mulch. Special wavelength selective mulch (IRT) will allow for more soil heating that black plastic, however the difference is not always enough to warrant the extra cost. Planting on IRT or black plastic mulch often gains 1-2 weeks. Early bare ground plantings using shorter season varieties can often make the 4th of July market. These are most successful on sandy soils that warm up more quickly. Some growers have had success with early plantings grown on ridges to speed warming even more. Bicolor varieties are often used for these early plantings due to their better cold tolerance.
Processors in the region are switching more acreage to supersweet production. They are also interested in planting as early in April that will still allow for good stands. Seed companies developing processing supersweet varieties have made great strides in improving cold tolerance for these early plantings. Company fieldmen also spend time working with seed companies to identify the highest vigor seed lots for planting early. Growers also have an important role to play in the success of early processing sweet corn plantings. Early plantings will require shallower seed depths and planters need to be adjusted so that seed is placed uniformly at the proper depth and so that there is good soil to seed contact. Fields that warm up quickly should be selected for early plantings and should be worked well ahead of time. Remember that the wetter a soil is, the longer it will take to warm up. If at all possible, plant on a warming trend. Soil temperature around the seed should be >60°F during the day for best germination.