Fresh from your own bed, sweetcorn is a revelation: sweet, juicy and worlds away from the tin. Growing it is easy once you understand a single peculiarity that many gardeners learn too late. Corn pollinates by wind, and that changes everything about how you plant it.
Plant corn in one pretty single row and you often harvest disappointingly gappy cobs with half-empty tips. Plant it in a block and you harvest full, juicy cobs. That is what we tackle first.
Why you plant corn in a block
Corn carries two separate flowers. At the very top sits the male tassel, which releases the pollen like a fine dust. Lower down sits the cob, from which the fine silks hang out. Each single silk leads to exactly one kernel and must catch a grain of pollen for that kernel to fill.
But the pollen does not fly far, it simply falls down and sideways. In a single row it blows into the void. When the plants stand close together in a compact block, however, the pollen reliably sifts onto the neighbouring cobs. Hence the rule of thumb: better a square of four by four plants than one long line.
How to grow sweetcorn
Start warm
Corn only germinates in warm soil. Sow direct from mid-May after the last frosts, or pre-grow in pots from late April. Pre-grown plants give you a two to three week head start.
Plant out in a block
Set the plants about 40 cm apart in a square bed, at least four by four. That is how wind pollination works. Timing: roughly CW 18 to 22.
Give it nitrogen
Corn is a hungry heavy feeder. Work in ripe compost and feed organically at flowering. Pale, light-green leaves are a sign of hunger.
Water well at flowering
When the tassel and silks appear, water decides how well the cobs fill. Keep the soil evenly moist during this time.
Harvest at the milk stage
Once the silks are brown and dry, do the nail test: press a kernel open and if the sap is milky, the cob is ripe. Clear sap means too early, doughy too late.
A common mistake hides in the choice of variety right next to the bed. Different types of corn can cross by wind, and you taste it at once.
Corn in a block, not in a row. The wind does the rest when the plants stand close together.
The core rule for full cobs
Corn, bean and squash: the Three Sisters
Corn combines wonderfully with other crops. The best known is the ancient milpa, or Three Sisters planting.
The corn gives the pole beans support to climb. The beans gather nitrogen and so feed the hungry corn. The squash shades the ground with its large leaves, keeps it moist and holds back weeds. Three crops on one patch, each helping the others.
Frequently asked questions
How many corn plants do I need at least?
For reliable pollination, at least sixteen plants in a four-by-four block. Fewer is possible, but then the cobs often fill only partly. More is better.
Why are my cobs empty at the tip?
That is almost always poor pollination, often because the corn stood too isolated or it was too dry at flowering. Every empty spot is a kernel whose silk caught no pollen.
Can I help by hand?
Yes. On a dry morning, shake the tassels so the pollen falls onto the neighbours' silks. Or catch pollen in a bag and dust it onto the silks on purpose.
Why does shop-bought corn often taste bland?
Because the sugar turns to starch quickly after harvest. Corn you pick yourself and cook the same day is noticeably sweeter. Supersweet varieties hold the sweetness a little longer.
