Corn
Zea mays subsp. mays
Poaceae · grass family
Origin · Mesoamerica
- Matures
- 2–3 months
- Harvest
- Once · Annual
- Sun
- 6–8+ hrs
- Spacing
- 12 in
Planting window
When to sow, by microclimate — foggier blocks run a different calendar than sunnier ones.
| Jan | Feb | Mar | Apr | May | Jun | |
|---|---|---|---|---|---|---|
| Foggy | ● | ● | ● | |||
| Sunny | ◐ | ● | ● |
| Jul | Aug | Sep | Oct | Nov | Dec | |
|---|---|---|---|---|---|---|
| Foggy | ◐ | |||||
| Sunny | ● |
Sunlight
How well it does at each level of direct sun per day.
Soil depth
Root room it needs — useful for sizing raised beds and containers.
Soil pH
The soil acidity it grows best in — most crops sit just below neutral, so this mostly matters for heavily amended or long-reused beds.
- Preferred range
- pH 6.0–6.5
Spacing
Room each plant needs — along the row and between rows — for sizing beds.
- In-row
- 12 in
- Between rows
- 36 in
Growth habit
The shape it makes in the bed and how tall it gets — what tells you whether to give it a trellis, a stake, or just room.
- Habit
- Upright
- Mature height
- 5–8 ft
Stands on its own; the tallest types appreciate a stake in wind.
Growing in containers
Whether it does well in a pot, planter, or window box — the SF balcony-and-deck question, weighing its footprint, form, and staying power, not just root depth.
Workable in a large, deep container with attentive watering and feeding.
How to start it
Sow it where it grows, or raise it under cover and set it out — and how far ahead to start the seedlings if it's the latter.
- Usually
- Direct-sow
Sown straight into the bed it will grow in.
Getting started
How it goes in the ground — how deep to sow or set it, and the soil temperature it needs to wake up. The cold-soil floor is the real limiter for direct-sowing in a foggy SF spring.
- Started from
- From seed
- Ideal soil temp
- 65–95°F
- Sow depth
- 1–1.5 in
- Time to emerge
- 3–12 days
Germinates between 50–105°F; happiest around 65–95°F.
Watering & feeding
How thirsty and how hungry it is — the water it wants and how much feeding the bed needs to keep it producing. In the fog belt even a thirsty crop drinks less than it would inland.
- Water need
- High
- Feeding
- Moderate feeder
A thirsty crop — keep it consistently moist; dry spells cost it flavor, texture, and yield.
A balanced feed worked into the bed at planting usually carries it through the season.
A heavy drinker — keep it well watered, especially at tasseling, silking and ear fill, when drought cuts yield and quality most. A moderate feeder by the UGA scale (though it draws nitrogen steadily).
Pests & diseases
What tends to trouble this crop — what it is, what you'll see, and what to do about it, least-toxic first.
Corn earworm is managed differently on corn than on other crops: consider not treating at all and simply cutting the damaged ends off the ears at harvest, or apply a few drops of mineral oil to the silks just inside each ear 3 to 5 days after the silks first appear.
Pests11
Aphids
- What it is
- Aphids have soft pear-shaped bodies with long legs and antennae and may be green, yellow, brown, red, or black depending on the species and the plants they feed on. A few species appear waxy or woolly due to the secretion of a waxy white or gray substance over their body surface.
- What you'll see
- Low to moderate numbers of leaf-feeding aphids aren't usually damaging in gardens or on trees. However, large populations can turn leaves yellow and stunt shoots; aphids can also produce large quantities of a sticky exudate known as honeydew, which often turns black with the growth of a sooty mold fungus.
- What to do
- Before planting vegetables, check surrounding areas for sources of aphids and remove these sources. On the other hand, these aphid-infested weeds can sometimes provide an early source of aphid natural enemies.
Armyworms
- What it is
- Armyworm larvae feed in groups, which distinguishes them from other vegetable pests such as corn earworms and loopers. Markings on newly hatched armyworms are usually hard to distinguish from those of other caterpillars; older larvae have distinct lengthwise stripes.
- What you'll see
- Armyworms may feed on the crowns of seedlings. On larger plants, armyworm caterpillars skeletonize leaves.
- What to do
- Handpick. Virus diseases, parasites (Hyposoter and Trichogramma), and general predators may be effective on caterpillars.
Corn Earworm or Tomato Fruitworm
- What it is
- The corn earworm or tomato fruitworm is a common caterpillar pest of many vegetables and flowers. Newly hatched larvae have several rows of dark bristles on their backs.
- What you'll see
- Earworms feed on leaves, buds, and flowers of many vegetable crops. They destroy seedlings, bore into lettuce heads and bean pods, make deep watery cavities in fruit, and leave frass.
- What to do
- Handpick, and avoid spraying with insecticides. Bacillus thuringiensis may kill 40 to 60% of the population but must be applied just after eggs hatch and before caterpillars enter fruit.
Cucumber Beetles
- What it is
- Adult beetles are shiny with black heads, long antennae, and about 1/4 inch long. Adults may be striped or spotted, depending upon species.
- What you'll see
- Adults feed on the leaves of many vegetables as well as on soft fruit. Shoots and blossoms may also be consumed.
- What to do
- Management of cucumber beetles is difficult. The best strategy for most vegetable gardens may be to place protective cloth over emerging plants and remove it when plants are old enough to tolerate damage.
Cutworms
- What it is
- Cutworms are dull brown caterpillars ranging in length from 1 to 2 inches when fully grown. They curl into a C-shape when disturbed.
- What you'll see
- Cutworms feed on blossoms and leaves of many ornamental plants and attack most garden crops. They clip off seedling stems near or just below the soil level.
- What to do
- Cutworms are pests mainly in the spring. Destroy crop residues; keep garden weed-free in winter.
Earwigs
- What it is
- The adult earwig is readily identified by a pair of prominent appendages that resemble forceps at the tail end of its body. Used for defense, the forceps are somewhat curved in the male but straighter in the female.
- What you'll see
- European earwigs feed on a variety of dead and living organisms, including insects, mites, and growing shoots of plants. They are voracious feeders on soft-bodied insects such as aphids and insect eggs and can exert significant biological control under some circumstances.
- What to do
- Management of earwigs requires an integrated program that takes advantage of their habitat preferences. Initiate a regular trapping program.
Flea Beetles
- What it is
- Their small size, enlarged back legs, characteristic shot-hole damage, and habit of jumping when disturbed make flea beetles easy to identify. There are numerous flea beetle species.
- What you'll see
- Adults feed mostly on leaves, leaving tiny pits or small holes at their feeding sites. Flea beetles feeding together can cover leaves with bleached, pitted areas or ragged holes.
- What to do
- Remove debris in the fall to remove any overwintering beetles. Reflective mulches applied very soon after planting and before plants become infected can be helpful.
Seedcorn Maggot
- What it is
- Seedcorn maggot larvae are small, legless, white maggots usually less than 0.33 inch when full grown; the head end is pointed and the rear is blunt. Adults are dark gray flies about half the size of the common housefly.
- What you'll see
- Maggots kill germinating seeds and very small seedlings. Once the stand is established and seedlings have developed a few leaves, maggots are unlikely to cause economic damage.
- What to do
- Cool, wet weather promotes seedcorn maggot infestations. Avoid overfertilization with manure; maggots prefer to lay eggs in rich soil.
Spider Mites
- What it is
- To the naked eye, spider mites look like tiny, moving dots; however, you can see them easily with a 10X hand lens. Adult females, the largest forms, are less than 1/20 inch long.
- What you'll see
- Mites cause damage by sucking cell contents from leaves. A small number of mites usually isn’t reason for concern, but very high populations—levels high enough to show visible damage to leaves—can damage plants, especially herbaceous ones.
- What to do
- Cultural practices can have a significant impact on spider mites. Midseason washing of trees and vines with water to remove dust may help prevent serious late-season mite infestations.
Thrips
- What it is
- Most adult thrips are elongate, slender, minute (less than 1/20 inch long), and have long fringes on the margins of both pairs of their long, narrow wings. Immatures (called larvae or nymphs) are oblong or slender and elongate and lack wings.
- What you'll see
- Thrips feeding on plants can damage fruit, leaves, and shoots and very noticeably affect plants’ cosmetic appearance. However, thrips rarely kill or threaten the survival of trees and shrubs.
- What to do
- Thrips species that feed on many different plant species often move into gardens and landscapes when plants in weedy areas or grasslands begin to dry in spring or summer. Avoid planting susceptible plants next to these areas, and control nearby weeds that are alternate hosts of pest thrips.
Vegetable Leafminers
- What it is
- Adult leafminers are small, active, black flies often with a prominent yellow triangle between the bases of the wings. The head behind the eyes is mostly black.
- What you'll see
- Leafminers attack many different vegetable and flower hosts, including cole crops, cucurbits, tomatoes, peas, beans, aster, begonia, dahlia, impatiens, lily, marigold, petunia, and verbena. Adult female leafminers puncture leaves and sometimes petals to feed on exuding sap.
- What to do
- Leafminers rarely require treatment in gardens. Clip off and remove older infested leaves.
Diseases4
Bacterial Soft Rot of Corn
- What you'll see
- Bacterial soft rot first appears as rapid desiccation of the youngest leaves. A soft, watery rot of leaf tissue occurs inside the leaf whorl.
- What to do
- The disease is most commonly encountered in sprinkler-irrigated gardens or when unseasonal rains occur. If soft rot develops, avoid overhead sprinklers.
Common Rust on Corn
- What you'll see
- Common rust causes pustules that may appear on any aboveground part of the corn plant but they are most abundant on leaves. The pustules, which may erupt and become powdery, occur nearly simultaneously on both leaf surfaces.
- What to do
- Common rust is favored by cool temperatures and high humidity or overhead sprinklers. Some resistant varieties may be available.
Common Smut of Corn
- What it is
- Head smut may be confused with common smut. However, the vascular bundles within the galls of head smut readily differentiate head smut from common smut.
- What you'll see
- Common smut is easily recognized by the tumorlike galls that form on any aboveground plant part. Galls at first are a glistening, greenish white to silvery white.
- What to do
- Remove and destroy tumorlike growths as soon as noticed; keep the black powder in galls from getting into the soil. Plant early as common smut becomes more prevalent in later harvests.
Head Smut of Corn
- What it is
- Head smut may be confused with common smut. However, the vascular bundles within the galls of head smut readily differentiate head smut from common smut.
- What you'll see
- Head smut is characterized by large smut galls that replace ears or tassels. The galls are first covered by fragile, creamy white membranes that eventually rupture to release masses of dark brown spores.
- What to do
- Spores from the head smut fungus survive in the soil for long periods. Resistant varieties may be available.
Harvest & storage
How to tell it's ready to pick, and how to keep it once it's in.
- Keeps
- DaysBest eaten within a few days of picking.
- Ready to harvest
- Pick about three weeks after the silks appear, when they have browned and a punctured kernel runs milky — the sugars fade fast, so eat it the day it's picked.
- Storing
- Refrigerate in the husk and eat within a day or two; the sugar turns to starch quickly.
Culinary use & nutrition
What it's for in the kitchen, and the nutrients a 100 g raw serving is a notable source of.
In the kitchen
- Boiled / steamed
Nutrition highlights
- Good source
- Thiamin, Niacin, Folate
Share of the Daily Value in a 100 g raw serving (USDA FoodData Central).
Pollinators & wildlife
What this crop offers the garden's wildlife once it flowers — often the payoff for letting a bolting plant stand.
No notable draw for pollinators — its flowers offer them little.
Wind carries the pollen from tassel down to silk; bees will help themselves to a little of it, but corn keeps no nectar and offers a flower nothing like a petal.
Companion planting
What grows well nearby, and what to keep apart.
The center of a three-sisters planting: pole and runner beans climb the stalks and fix nitrogen for all three, while squash sprawls below to shade out weeds and even deter raccoons from the ears. A strip of flowering insectary plants nearby (buckwheat, cowpea, sunn hemp) pulls in the predators and parasitoids that keep corn earworm down.
Sources
Growing data on this page is drawn from UC Master Gardeners, San Mateo–SF Counties, Golden Gate Gardening (Pam Peirce), and the other references on our sources page.