To tell when corn is ready to harvest, several key indicators can be used depending on whether you are growing sweet corn for fresh eating or field corn for grain or silage:
For Sweet Corn (Fresh Eating)
- Silk Color and Texture: The silks on the ear should be dark brown to black and dry or crispy at the tips
- Milk Stage of Kernels: Pierce a kernel with your fingernail; if a milky liquid comes out, the corn is at the ideal "milk stage" for harvest. Clear liquid means it's not ready, and opaque liquid means it's overripe
- Ear Feel: The ear should feel full and rounded, especially near the tip under the silk. If it feels thin or hard at the tip, it is not ready
- Timing: Typically, sweet corn is ready about 17 to 25 days after silks first appear
For Field Corn (Grain or Silage)
- Milk Line on Kernels: Break an ear and observe the "milk line" where the milky and starchy parts meet on the kernel. When the milk line is about halfway down, kernels have about 40% moisture and harvest is 2–3 weeks away
- Black Layer Formation: This is the physiological maturity stage (R6), occurring about 55 to 60 days after silking, indicating the kernels have reached maximum dry weight and are ready for harvest soon
- Moisture Content: Ideal harvest moisture for grain corn is about 15-18%. For silage, total plant moisture is usually between 60-70% when the milk line is ½ to 2/3 down the kernel
- Silk and Husk Color: For field corn, husks turn brown (not green), and silks are darkened when ready
Practical Tips
- Monitor the silking date and count about 55-60 days for field corn maturity
- For sweet corn, watch the silks and test kernels regularly during the milk stage since it only lasts about a week
- Use a small cut in the husk to check kernels without exposing the ear to pests
- For silage corn, consider weather conditions as drying rates vary; cooler, wetter weather slows drydown
In summary, harvest sweet corn when silks are dark and kernels release milky juice, and harvest field corn when the milk line progresses down the kernel and black layer forms, with moisture content suitable for your intended use
