Corn

Ancient corn known as maize from areas near the Andes eventually hybridized with other grasses to become the field corn grown world-wide today. Succulent sweet corn was a spontaneous mutation in field corn and continues to be hybridized by commercial breeders. Popular in summer kitchens and home gardens, sweet corn comprises only about 1% of all corn grown.

Selecting Sweet Corn Varieties

  • Besides colorful ornamental ears and popcorn, there are 3 types of sweet corn varieties.
    • Standard sugary are older types with sugar converting rapidly to starch after harvest.
    • Sugary-enhanced corn has been bred to increase more sweetness than earlier varieties.
    • Super sweet are the most recent developments and sweetest as starch converts very slowly to sugar. Refrigeration slows starch conversion even more.
  • Numerous varieties range from white to yellow to bicolor and in length of time to harvest.

Growing Techniques

  • Evaluate your microclimate before planting. Very cool and foggy summers do not support consistent growth and pollination.
  • Dig in compost or well-rotted manure before planting. Enrich poor soil by adding nitrogen fertilizer, such as fish emulsion, during early growth.
  • Plant corn May-July. Corn does not tolerate frost and germinates poorly in cold soil.
  • Soak shrunken kernels a few hours or overnight prior to planting; plant in moist soil.
  • Direct seed 2-3 kernels per hill, 1 in. deep—or set out transplants—every 10-12 in. in rows 2-3 ft. apart; or plant in double rows 10-12 in. apart with 2½–3½ ft. between double rows.
  • Plant corn in a block with a minimum of 3 rows, at least 4 ft. by 4 ft. for best wind pollination. Pollination is more successful in blocks than in 1 or 2 long rows.
  • Separate super sweet varieties by at least 300 yards from other types to prevent cross pollination and loss of desirable characteristics.
  • Remove any stunted shoots; transplant crowded strong shoots 3-4 in. tall to fill gaps in rows.
  • Water adequately to produce full, juicy ears; corn does not do well in drought conditions.
  • Make successive plantings every 2 weeks by planting early-, mid-, and late-season varieties, using only the earliest varieties for late-summer crops to allow enough time for ears to mature.

Harvesting Ears

  • Expect to harvest 20-40 ears from a 3- or 4-row block in 60-110 days or longer after sowing, or about 2-3 weeks after the first silk strands appear.
  • Watch for shriveled, brown silks at the tops of green husks and plump ears to indicate maturity.
  • Identify the “milk stage” for harvest by puncturing a kernel with a fingernail or sharp knife. Clear liquid indicates immature corn; completely white liquid indicates overripe or starchy ears.

Pests and Problems

  • Protect young shoots with a floating row cover, or sow indoors and transplant when seedlings are larger and less vulnerable to birds, cutworms, earwigs, slugs and snails. 
  • Use a strong spray from the garden hose to blast off aphids.
  • Cut off ends before cooking ears if corn earworms enter the silk end and chew kernels.
  • Remove or retain any grayish-black fungal corn smut, a non-poisonous, edible gall.

Additional Information

February 2022

Source URL: https://oc4h.ucanr.edu/site/uc-master-gardener-program-sonoma-county/corn