Have you spent months carefully attending to corn in your garden for little or no yield, or watched corn ears grow over weeks to be disappointed by scattered kernels per ear at harvest? If so, you’re not alone. Corn is a demanding vegetable, with a long list of needs for successful harvest of kernel-filled ears. Even the most skilled gardeners may be hard-pressed to produce consistently full corn ears under challenging growing conditions in some areas of California.
More so than most other vegetables, corn requires abundant sunlight, soil macronutrients, space, and water. It is fussy about temperature and needs warm-but-not-hot weather for germination, growth, pollination, and optimal development of ears and kernels. It is also fussy about pollination and tends to produce ears with missing kernels in the home garden. It needs fertilization with nitrogen at least until silks form.
Under adverse conditions for pollination, such as row planting in the home garden or as a result of cold or hot weather, corn may produce few-to-no kernels per ear. It is prone to insect pests, which may rapidly damage ears as they ripen, or, as it so often seems, infest the largest and best ears in the final days before harvest. It suffers from too much or too little water, and is sensitive to almost any root disturbance, including transplanting.
Despite its challenges, what a wonder homegrown corn can be when cooked fresh and enjoyed with friends or loved ones. The following tips should put you well on your way to success with corn:
1) Time corn plantings carefully to grow and mature during warm-but-not-hot weather. Corn grows best at 77°F to 91°F, with ideal nighttime temperatures in the 60s to low 70s. Corn grows slowly and may not develop ears at temperatures below about 50°F or above 95°F. See below for detailed information about suitable temperatures for growing corn.
2) Plant in full sun. More so than most vegetables, corn needs abundant sunlight.
3) Seed directly into fertile soil. Corn germinates best when planted into warm, moist soil at temperatures of at least 65°F to 75°F, and germinates fastes and with a higher germinate rate at warmer temperatures of 80°F to 95°F. Supersweet corn types tend to be more sensitive to cold soil. When corn seeds are sown directly into pre-irrigated soil, they often will not need additional water until after germination. This method may help avoid overwatering seeds, which can contribute to poor germination or seed rot. Corn is sensitive to being planted in cold soils below 65°F. Garden Zeus recommends untreated corn seeds (treated corn seeds may germinate well at soil temperatures as low as 50°F).
Early Sunglow hybrid corn tolerates cooler weather than other corn varieties, and is an ideal sweet corn for planting in cool soils. Painted Mountain is a unique cold-tolerant modern field corn that can be eaten fresh as sweet corn when ears are young.
4) Don’t plant corn in rows in the home garden. GardenZeus expert Darren Butler recommends a minimum bed or block size of 8 feet by 4 feet (32 square feet); larger is better, preferably in sections that are at least 4 feet wide. Corn needs thorough pollination to produce ears full of kernels, and is primarily pollinated by wind. Rows of corn in home gardens generally don’t provide enough corn plants spaced close enough together for effective pollination. Planting corn in rows is appropriate in fields or mass-plantings of 1/4 acre or more, or when heavy machinery will be used for sowing and harvesting.
How many seeds do I need to plant corn in blocks? You will need about 20 to 30 grams (about 3/4 to 1 ounce) of corn seeds to plant 30 to 40 square feet of corn spaced at 4 to 6 inches for later thinning. Some corn seed packets may include only 10 or 12 grams (about 1/3 to 2/5 ounce) of seeds.
5) Don’t mix plantings of sweet corn with other types of corn. Sweet corn ears that are pollinated by flour corn, field or dent corn, popcorn, or supersweet corn will become tough and starchy, which ruins their flavor and texture. Hundreds of feet of minimum separation is needed between stands to avoid cross-pollination and preserve the eating quality of sweet corn. When in doubt it’s best to plant sweet corn only with no other corn varieties in a single garden, or time plantings so sweet-corn pollination will be completed and ears maturing before any other corn varieties are in flower.
Sweet, hybrid sweet, and supersweet corn varieties are often not the best choice for a community garden as the likelihood may be high of cross pollination by other corn types.
6) Provide sufficient, even moisture and don’t overwater. Corn requires consistent moisture in well-drained soil, especially during seedling growth, during the critical pollination period after the emergence of the corn silks or tassels, and during development of kernels. It suffers in wet soil at every growth stage, from seed germination to mature plant.
7) Provide sufficient compost and macronutrients. Corn is a very heavy feeder, and needs sufficient nitrogen, phosphorous, and potassium. In nearly all soils, corn needs supplemental nitrogen throughout the growing season. Corn is less extreme in its demand for secondary nutrients (calcium, magnesium, and sulfur), and micronutrients.
Suitable temperatures for growing corn: Corn tolerates short periods at both freezing temperatures and at very hot temperatures above 105°F. The ideal daytime temperature range for growing corn is 77°F to 91°F, with ideal nighttime temperatures in the 60s to low 70s. Corn grows slowly and may not develop ears at temperatures below about 50°F or above 95°F. Although corn thrives in warm weather, it does not like hot weather: plants may become stressed, leaves may sunburn, and corn pollination may become irregular or problematic at temperatures above 95°F, all of which may result in poor kernel development. Corn silks tend to dry out at temperatures in the mid-90s or hotter, which can result in poor pollination and ears with partial or spotty kernel development.