Sweetcorn is most successful in long hot summers, though many modern cultivars are better suited to cooler climates.
‘Supersweet’ cultivars are much sweeter than older varieties and retain their sweetness for longer; however, they are less vigorous. ‘Extra tender sweet’ corn is a less chewy form of ‘supersweet’ ideal for growing in the garden. Do not grow Supersweet cultivars close to other cultivars, as cross-pollination reduces the sweetness.
Sweetcorn does not germinate when soil or compost temperatures are below 10C (50F).
Sow at 18-21C (65-70F) from mid-April to early May in modules or deep pots at a depth of 2.5cm (1in). Use early, mid season and late varieties to extend the cropping season. Sow 2-3 seeds per pot and thin to leave the strongest seedling.
Harden off and then plant out indoor-raised plants at the end of May or early June depending on the weather.
As the plants are wind pollinated they should be grown in blocks rather than rows, 45cm (18in) apart. Conversely, there are some mini sweet corn cultivars which are harvested before fertilisation, and so don't need to be grown in a block and can even be grown as a windbreak.
Grow sweet corn in a sheltered, sunny position, protected from strong wind, on any fertile garden soil. Add up to two bucketfuls of organic matter, such as rotted manure, and also rake in 100g per sq m (3oz per sq yd) of Growmore before planting. Plants are less successful on dry or heavy soil.
Mulch with organic matter, to conserve moisture and suppress weeds and mound soil over the roots, which appear at the base of the stems. Hoe carefully as they are shallow rooted.
Stake plants individually if they are tall or the location is exposed.
Water well in dry weather; this is vital when the plants are flowering. Tap the tops of the plants when the male flowers (tassels) open to help pollination; poor pollination results in sparsely filled cobs. Liquid feed when the cobs begin to swell.
Test for ripeness when the tassels have turned chocolate brown - squeeze a grain between thumbnail and fingernail; if a watery liquid squirts out, it is unripe; if it is creamy, the cob is ready; if paste-like it is over-mature. Twist ripe cobs from the stem. They rapidly lose their flavour so have a pan of boiling water ready before you harvest, ready to plunge them in.
‘Lark’ AGM: (Extra tender sweet) Early and high yielding with sweet, tender, top quality cobs
‘Earlibird' AGM: (Supersweet) 2nd early. Vigorous plants with good sized, uniform cobs
‘Golden Giant’ AGM: (Supersweet) A vigorous main crop with large, good quality cobs.
Sweetcorn ‘Swift’ F1: (Extra tender sweet) One of the best varieties to choose for growing your own sweetcorn in the UK. Plenty of cobs.
Mice: These rodents will eat the seeds of sweetcorns when planted
Remedy: Place traps around the area where sweetcorn seeds are sown.
Birds: Jays and pigeons damage ripening crops
Remedy: Either net the entire crop or place plastic bags over individual cobs.
Slugs and snails: These feed on the young seedlings and you'll see the tell tale slime trail on the soil around your crop, as well as on the leaves.
Remedy: There are many ways to control slugs and snails, including beer traps, sawdust or eggshell barriers and copper tape.
More information on slugs
More information on snails