How to Grow Sweetcorn – A Guide to Growing Sweetcorn
Straight from the plant, sweetcorn is one of the most delicious vegetables for the home grower. Sweetcorn used to be a difficult crop to grow away from the south of the country as it needed a long, warm growing season. However, the development of new varieties has changed that. It still needs a long growing season but the main reasons for failure are overcrowding and under feeding.
It produces masses of tall foliage and is not really suitable for container growing or close spacing.
Sowing and Growing Sweetcorn
- Sweetcorn needs a lot of nitrogen to provide food for its growth. It requires plenty of space and to be planted in a way that encourages pollination – poor pollination results in patchy development of the corn kernels.
There are two methods of cultivation. The first is my own fussy, but never fails to produce a good crop with a high germination rate from what is expensive seed:
- Start in late April–early May. Chit (or sprout) the seed first. Lay a sheet of damp kitchen paper in the base of a shallow, lidded container. Place the seeds on the paper and cover with another sheet of damp paper. Pop the lid on the container and put it in a warm, dark place (around 78ºF/20ºC – an airing cupboard is ideal). After three days check to see if any have sprouted, and then check daily. Usually, the seeds will sprout within a day or so of each other.
- As soon as the seeds have started to sprout, plant them 3 cm (1 inch) deep into multi-purpose compost in 8 cm (3 inch) pots or root trainers. You can also use toilet roll inner tubes filled with compost, but they tend to dry out quickly so wil need a daily spray with water if necessary (the tubes are planted out and will rot away in the soil). Water with tepid, not cold water, to avoid shocking the seedlings.
- Keep the seeds warm (over 50ºF/10ºC). Cover with fleece if cold, particularly at night. Warm the final planting position with a cloche or fleece before planting out.
- Once the plants are around 10 cm (4 inches) tall, plant out into holes 5 cm (2 inches) deeper than your pots, filling the holes to the soil level of the plants, so that they are sitting in a small depression. If you didn’t manure the soil the preceding winter, sprinkle a little dried blood or sulphate of ammonia around each plant to provide the nitrogen boost they need to get off to a good start. Cover with cloches and leave them on until the plants push them away with their own growth.
- When the plants reach 60 cm (24 inches), draw soil up around the stem, filling in the depression and a little above. This encourages strong root growth. Keep weed-free.
- In June apply a liquid feed to boost cob production, either a comfrey feed or a general purpose liquid fertilizer.
The alternative, simpler method of cultivation, standard:
- Sow directly into the soil mid-May, dropping two seeds in a hole 3 cm (1 inch) deep: if both seeds germinate, remove the weaker one. Cover with a cloche or use clear plastic 2-litre drinks bottles, with the bases removed, over each plant as mini-cloches.
- If the leaves look yellowish or the plants do not seem to be growing quickly, try a high-nitrogen liquid feed which should effect a fast recovery.
- Plant out in blocks (not rows or you’ll get poor pollination), with at least 45–60 cm (18 inches–2 feet) between plants each way.
- Its a fine line between under-ripe and over-ripe, when the corn hardens.
- Sweetcorn is ready to harvest when the tassels hanging from each cob turn brown. Double check by carefully peeling back the leaves and pinching a kernel – if the juice is milky then they are ready to pick. Just twist the cob away from the plant.
Pests and Problems with Sweetcorn
- Pigeons can be a pest, pulling away the leaves and eating the kernels.
- Earwigs are partial to sweetcorn. Try stuffing plant pots with hay or shredded paper and placing them in and around the plants. The earwigs will hide in the pots – just shake them out, well away from your vegetable garden.
- Poor pollination can cause some or even all of the kernels not to develop on the hob. The pollen forms on the flower head tassels at the top of the plant and drops down onto the silks – the fine long hairs – growing on the forming cobs. Planting too closely can prevent the pollen reaching target. To assist pollination tap the stalks so the pollen sheds down to the silks on calm days.
Varieties of Sweetcorn
- The ‘super sweet’ F1 varieties are extremely tasty. The ‘tender sweet’ have a less chewy texture.
- Lark F1 is an excellent variety; Sundance F1 is better for freezing and more reliable if you live in the north.
- Never inter-mix varieties as they will cross-pollinate, with unpredictable results. If you do grow two varieties, they must be at least 8 metres (27 feet) apart.
- The connoisseur’s advice is to put a pan of water on to boil and then run (not walk!) back to the kitchen with your freshly harvested cobs, since the moment they are picked, the natural sugars begin to turn to starch.
- However, sweetcorn keeps well for a week or so in the fridge and a glut can be frozen on or off the cob.
- Try the cobs on the barbecue, leaving them in the leaves for protection as the corn cooks in its own steam.