Sweetcorn is one of the most rewarding of all home-grown crops. But it is not the easiest and it does take up a lot of space so is not for everyone. Sweetcorn is the same basic plant as maize but has been bred to be sweet. There are now Supersweet cultivars that are much slower to convert the sugar in the kernels to starch. Most modern kinds and F1 hybrids will be this type. When growing Supersweets do not grow maize or popcorn close by or it may affect the sweetness of your sweetcorn. When looking for what to grow it is worth considering any that crop quickly to be sure that you get a decent crop. I usually grow the F1 bird series: ‘Lark’ and ‘Swift’ though there are others such as ‘Goldcrest’. The latest cultivars have white kernels or a mix of white and yellow but, since the yellow colour is of nutritional benefit I can’t quite see the point.
Because sweetcorn is a grass, it is wind pollinated and pollination is necessary or you won’t get a crop. The pollen, on the male flowers or tassels are held at the top of the plant (above). The potential cobs (below) are produced lower on the plant and, depending on how well the plants have grown, you will get one or two female cobs on the main stem and there will be several, smaller shoots from the base. The pollen has to drop from the top of the plant onto the lower, female cobs, helped by the wind.
This brings us to one of the most important keys to a good crop – planting in blocks. It is no good planting a row because there is then little chance of the pollen hitting the wispy tassels of the female cobs. All those ‘silks’ have to be hit by a pollen grain – each one is connected to one kernel. If pollination is poor, you end up with a cob with only a few kernels and that is really disappointing. So we plant sweetcorn in blocks so that all that pollen, pouring from the stamens above, has a chance to hit the silks. If you consider a block 4×4, only four of the sixteen plants will actually be surrounded by plants. Plant 5×5 and nine plants will be: 6×6 and 16 will be. The bigger the block is, the better the pollination prospects. Bearing in mind that wind will blow the pollen around it doesn’t mean that plants around the edge are useless – far from it – just don’t plant in rows.
You can grow sweetcorn in a polytunnel, but it takes up a lot of room – and you will have to tap that pollen down. You can also grow it in a pot on the patio but there really is no point in growing three plants – and think of the crop of tomatoes or courgettes you could get in the same space – and for the same effort!
Outside, a sunny, sheltered spot with light, fertile soil is best. Sweetcorn needs warmth and though you can sow it where it is to grow, it is best to start it under glass or on a windowsill so you have small plants to set out after the last frost of spring – sometime in May in Ireland and the UK. When sowing, sow in individual pots. Do not buy pots with a clump of seedlings you have to pull apart. I would say don’t buy seedlings anyway because you won’t know the variety and you need the best seeds for the best crop. Sow the seeds about six weeks before you think you can plant out – no more. You need to plant them out as stocky little plants – if they are sitting on the windowsill, getting tall and floppy you are on a bad start. They are perfect when about 10-15cm tall. It is important to harden them off before planting – getting them acclimatised to outdoor conditions. You can do this by putting them out on shady days, bringing them in at night, for a few days, then leaving them out all the time apart from cold nights. If you plant them out on a sunny day when they have been on the windowsill, the leaves will scorch.
But sowing first. I sow in cell trays. I fill with compost and place two seeds per cell on the compost and then push them in, about 1cm deep, with the blunt end of a pencil, adding a scattering of compost if necessary to fill the holes. If the seeds are expensive sow one per cell – I will remove the weaker of the two if both grow – but you will find you have some gaps because not every seed will grow.
When your seedlings are ready to plant, plant in a block with the seedlings 30-40cm apart. If the weather is a bit nasty you can cut the base off 2litre plastic bottles and use them as mini- cloches, leaving them in place for a week or so.
Then just keep them watered and weed-free and, as they grow into plants about 1.5m high, you will see the female cobs developing on the sides of the main stems and the male flowers will appear at the top.
The next trick is knowing when the cobs are ready to harvest. In theory the cobs are not at the peak of perfection for long and they deteriorate quickly after picking but the modern kinds are a bit more forgiving. Even so you need to eat sweetcorn when it is ready and not when you fancy it. As the cobs get over-mature the kernels become tough and the sugar turns to starch so they are less sweet. Picked fresh and at its best sweetcorn is delicious raw and I reckon that I eat most of mine in the garden, straight off the plant. It is not the most sensible crop to grow but it is high on my list because it is so delicious.
You can tell if the cobs are ready by a two stage test. Firstly, the silks will have turned brown and withered. When you see this you can then pull back the end of the sheaf to expose the top kernels and push your thumbnail into one. If the juice runs clear leave them a bit longer but if the juice is milky, snap the cob downwards, rip off the cover and tuck in.
Now there are a few other troubles I need to mention. These are tall plants and in exposed sites they can get smashed in autumn gales. And then there are rodents. Rats love sweetcorn and, as I have discovered, so do badgers. Rats eat the cobs without doing much obvious damage while badgers will pull the plants to shreds. Squirrels do the same sort of damage as rats.
I know this all sounds like a faff but sweetcorn really is a great thing to grow at home. If you want to get fancy you could try the ‘three sisters’ combination of climbing beans and squash with them. It does work but do now sow the climbing beans until the corn is well established so the beans have something strong to climb up. Plant trailing squash below the corn when the corn is starting to grow well. This way you get three crops from the same spot. Traditionally this is done with maize, not sweetcorn, but it does work. The only issue is that the three crops will not be ready at the same time because, unlike the Iroquois, we are not growing maize and probably French beans for eating fresh rather than for drying. So the beans, which will add nitrogen to the soil, will not benefit the corn as much as it would maize, but the squash won’t complain.