Sweetcorn

Sweetcorn is delicious steamed then eaten simply with a knob of butter, fresh from the garden. These tall plants also make a useful windbreak and an ornamental feature.

Jobs to do now

  • Water flowering plants
  • Check for ripeness

Month by month

Sow

Sweetcorn is most successful in long hot summers, although many modern cultivars are better suited to our cooler climate. You can buy early, mid-season and late cultivars – in colder regions, early cultivars will do best.

'Supersweet' cultivars are much sweeter than the older varieties and retain their sweetness for longer, but are less vigorous. Take care not to grow Supersweet plants next to other cultivars, as cross-pollination can result in poor flavour.

Another option is ‘Extra Tendersweet’ sweetcorn, which is almost as sweet and less chewy. 
 

Sow indoors

Sweetcorn needs warm conditions, so sow indoors at 18–21°C (65–70°F) from mid-April to early May. Sow the large seeds in modules or deep pots at a depth of 2.5cm (1in).

For an extended cropping season, try sowing early, mid-season and late cultivars at the same time, or sow one early cultivar another two times, three weeks apart.

Sow outdoors

Sow outdoors in late spring, in the ground or in pots. Make sure the soil temperature is above 10°C (50°F).

As sweetcorn is wind pollinated, plants should be grown in blocks rather than rows, 45cm (18in) apart. Sow two or three seeds at each point, then thin out the extra seedlings to leave just the strongest one.

Grow

Grow

Grow sweetcorn in a warm, sheltered, sunny position, protected from strong winds, and in fertile soil. Plants are less successful on dry or heavy soil.

Prepare the ground by digging in lots of garden compost or well-rotted manure. Then rake in a high potassium general fertiliser, such as Vitax Q4, at a rate of three handfuls per square metre/yard.

Sweetcorn is wind pollinated, so plant in blocks rather than rows, to maximise pollination. 

Mulch the soil with garden compost to hold in moisture and suppress weeds, and mound soil over any roots that appear at the base of the stems. Weed regularly, but hoe carefully as they’re shallow rooted.

Stake plants individually if they are tall or are being rocked by strong winds.

Water well in dry weather, especially when plants are flowering.

To aid pollination, tap the tops of the plants when the male flowers (tassels) open to help pollination of the female flowers below. Poor pollination results in sparsely filled cobs.

Harvesting

Sweetcorn cobs starts to ripen from mid-summer onwards. Once the tassels at the end of a cob have turned chocolate brown, test for ripeness – peel back a little of the husk and pierce a kernel with your fingernail. If a watery liquid squirts out, it’s not yet ripe, if the liquid is creamy, the cob is ready, but if it's paste-like then the cob is over-mature.

Twist ripe cobs and pull sharply from the stem.

Once picked, sweetcorn rapidly loses its flavour, so only harvest when required and eat as soon as possible.

Recommended Varieties

Common problems

Mice
Mice

These rodents will eat the seeds where planted

Remedy

Trapping can be effective for mice in a garden situation, although voles can be harder to control. Break-back traps of the type used against house mice can be effective when set in places where damage is occurring. Pieces of carrot or dessert apple are effective baits for voles, and peanut butter for mice. When using traps or baits out of doors, they must be placed under covers to reduce the risk of other animals interfering with them. Birds are particularly vulnerable to accidental trapping.

Birds
Birds

Birds, especially pigeons, can cause an array of problems including eating seedlings, buds, leaves, fruit and vegetables.

Remedy

Protect the plants from birds by covering them with netting or fleece. Scarecrows and bird-scaring mechanisms work for a while, but the most reliable method of protection is to cover plants with horticultural fleece or mesh.

Slugs and snails
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, copper tape and biocontrols.

Get involved

The Royal Horticultural Society is the UK’s leading gardening charity. We aim to enrich everyone’s life through plants, and make the UK a greener and more beautiful place.