Corn

Once soil at 2 inches has reached 60F, sow seed 1 inch deep, 7-9 inches apart, in rows 24-30 inches apart. Hold supersweet (sh2) seed back until the soil hits 65F (UMN Extension, https://extension.umn.edu/vegetables/growing-sweet-corn). Plant at least three or four short rows side by side rather than one or two long ones. Corn is wind-pollinated and every kernel needs its own silk caught by a falling pollen grain, so a single long row sheds most of its pollen into the neighbours' yard and gives you gap-toothed ears. Shrunken sh2 seed carries a smaller starch reserve and rots in cold ground where standard su seed germinates fine.

Rather than planting the whole patch at once, sow again every 10 to 14 days, or when the previous planting has three to four leaves. If you are growing a supersweet alongside a standard or sugar-enhanced variety, separate them by about 400 yards or sow them two weeks apart so they do not shed pollen together. Each planting ripens in one week-long rush, so a single sowing means a glut and then nothing. The separation matters because pollen from a su or se plant landing on a supersweet silk turns that kernel starchy - the cross spoils this year's ears, not just next year's seed.

From the first tassel through silking and ear fill, keep the soil evenly moist. This is the stretch where corn must not dry out, whatever else in the garden has to wait. A silk only carries pollen down to its kernel while it is still turgid, so drought at this moment aborts kernels outright. Stress here cuts yield, kernel quality and flavour at once, and corn gets no second chance - the ear is made only once.

Wait until the silks have reached full length and just begun to wilt and turn brown, about 5 or 6 days after half the patch has silked. Mix 1 part Btk with 20 parts vegetable oil and place 5 drops, about half a millilitre from an eyedropper, directly on the silk channel at the tip of each ear. The earworm moth lays on fresh silks and the larva crawls straight down the silk channel into the ear tip, feeding almost not at all on the outside of the plant - which is why broadcast sprays miss it. The oil sits in the channel the larva must pass through and carries the Btk to the one spot where it will actually be eaten.

When plants are knee high with 8 to 10 leaves, work about half a pound of 21-0-0 per 100 square feet into the soil alongside the row and water it in. Add another quarter pound when the first tassels or silks appear. Corn is a grass and a heavy nitrogen feeder, and it decides ear size during the fast growth just before tasseling. Starve it in that stretch and you get short ears that no amount of later feeding will lengthen.

In the late whorl stage, before the tassel emerges, examine 20 stalks at each of five spots across the patch. Look down into the whorl for tiny shot holes with a little light powdery frass beside them. Treat with a Bt product such as Dipel or XenTari if 30 or more of those 100 stalks are infested. For very early, high-value corn you may drop that threshold to 15. Borer larvae feed in the open whorl only briefly before tunnelling into the stalk, and once they are inside no spray can reach them. The late whorl is the single window where treatment still works, which is why you scout on a stage and not a date.

Start checking about 17 to 24 days after the first silks appeared. The ear is ready when the silks are dry and brown, the husk is still green, and the tip kernels are plump. Pull back a little husk and puncture a kernel with your thumbnail: clear juice means wait, milky juice means pick. The 17-to-24-day window swings with temperature, so the same variety ripens on a different date every year and in every zone - the calendar cannot tell you but the thumbnail can. Past milk stage the sugars turn to starch and the kernels go doughy.