When you sow sweet corn, that is, the corn we eat fresh off the cob, it’s important to always remember to isolate it from other corn varieties and especially from field corn (silage corn).
That’s because when the pollen from one variety of corn reaches the female flowers of another variety, this will give a mix of traits, not only in the coming generation, but in the kernels themselves, affecting texture, appearance and even taste.
The Whys and Wherefores
To understand this phenomenon, you need to know that corn undergoes double fertilization, a complex mechanism in which each pollen grain contains two male gametes (sperm cells). When a pollen grain sticks to a female flower, one gamete will fertilize the embryo to create a future plant, but the other will fertilize special nuclei that produce the endosperm, the part rich in starch and sugar that makes up the bulk of the kernel… and the part we like to eat. The result is that if you grow two varieties of corn side by side, the endosperm may have a mixture of genes and thus the taste of the kernel may well be affected.
If you grow your sweet corn, with kernels rich in sugar and low in starch, near field corn, with kernels rich in starch and low in sugar, pollen of the latter can fertilize your sweet corn, giving starchier, tougher kernels, midway between sweet corn and field corn.
Also, if you’re afraid of GMO contamination, you’ll probably find yourself eating home-grown GMO corn, at least in the US and Canada where GMO field corn reigns supreme. Yes, the added genes for insect resistance and herbicide tolerance will also be transferred to neighboring sweet corn.
Even if you grow two different sweet corn varieties close together, you may still have problems. I’m not going to go into details here, since sweet corn genetics is complicated, but suffice it so say that what gives sweet corn kernels their sugary taste can come from very different genes (su, se, sh2, etc.). So if the two sweet corn varieties count on different genes for their sweetness and the pollen of one type lands on the other, that will also adversely affect the taste.
Keeping Their Distance
The general recommendation for ensuring good sweet corn production is to isolate two varieties by at least 100 feet (30 m). Since corn is pollinated by the wind, there may be some cross-pollination even at that distance, but one or two starchy grains per cob won’t really affect the taste. On the other hand, if you want to save corn seed for next year’s crop, the kernel’s genetic purity is even more vital and an isolation distance of 250 feet (75 m) is best. In fact, some specialists suggest separating them by 1,000 feet (300 m)!
Separate in Time
In areas with a favorable climate, it is also possible to ensure good isolation between different corn varieties through temporal isolation. For example, you could sow an early corn variety near a late one and, provided that there are at least 14 days difference between the flowering dates, that will prevent cross pollination. Or you could sow two early corn varieties at least 14 days apart. However, temporal isolation is difficult to apply in short-summer regions where only one crop of early corn can normally be grown.
If you’re a home gardener, though, you probably won’t have isolation problems as long as you remember two things: to plant only one variety of corn per year… and not to live next door to a field of field corn!