There are three basic types of sweet corn: 'normal sugary', old fashioned types whose sugar is converted to starch relatively quickly: 'sugary enhanced', with generally higher levels of sugar that are converted to starch slower than the normal sugary types; and 'super sweet', which have sugar levels up to twice those found in normal sugary varieties. In the US, there is apparently a fourth type of sweet corn – called 'synergistic' – though we don't know much about it yet.
We only sell super sweet types, and the reason for this is simple: they not only have high concentrations of sugar, but they also stay sweeter longer, both before and after harvest. Unfortunately, though, their seed suffers from low vigour when sown in cold conditions. To overcome this problem we recommend starting your sweetcorn as transplants in a greenhouse, tunnel or windowsill.
Sweet corn takes more than three months from sowing to producing a crop, and unlike many vegetables, the harvest period is short. When sown at the same time, the three varieties we sell mature at different times; so growing all three should stretch out the harvesting period:
Do remember, though, that growing varieties to extend the harvest is not an exact science. The harvest periods between varieties will overlap to varying degrees, depending to a great extent on the weather.