When to harvest maize

Crop monitoring

When a maize crop is reaching its harvest date remember to walk the crop frequently. Walk into the crop at least 15-20 rows to get a representative view of crop maturity. Below are a list of things to watch as crop maturity starts to advance.

Crop colour 

  • The whole plant will typically still be green (unless moisture stressed or frost damaged).
  • Husk cover - this starts to yellow off/dry when the remainder of the plant is green.

Kernel maturity stage

As maize approaches maturity, plants mobilise water soluble carbohydrates (sugar) from leaves and stalk to lay down starch in the kernels. Starch accumulates first in the outer part of the kernel (closest to the inner husk). As maturity advances, starch fills from the outer part of the kernel, moving inwards towards the centre of the cob. Kernel milk line monitoring provides a handy guide to determine approximate:

  • DM percentage of the whole plant
  • Timing for crop harvest
NOTE: DM percentage of the whole plant can’t be determined accurately using kernel milk line position alone – planting date, weather and between hybrid variation mean that kernel milk line is a guide for harvest only. Whole plant DM% remains the ‘gold standard’ for assessing DM%.



  • Select 3-4 cobs at least 15-20 rows in from crop edge.
  • Strip husks, snap cobs in half, discard bottom half.
  • Hold top (tip) of cob, tip facing towards ground.
  • Milk line = junction between harder starch and softer milk endosperm.
  • Assess how far down the kernel the milk line has moved. Run fingernail or pen tip from outer starchy edge to milk line to identify the milk line.


  • Kernel milk line is only a guideline for probable harvest timing.
  • Whole plant DM% is the best way to be sure timing is right.
  • Harvest a number of individual plants from 15-20 rows into the crop. Use a garden shredder to process plants and cobs. Mix shredded whole plant material well and grab two to three large handfuls of chopped material.
  • Send to a feed testing laboratory for DM% analysis. Alternatively, microwave methods are useful for providing DM% results more quickly. Ask your Corson Maize Seed Sales Agronomist for more information about DM% testing of whole plants or refer to the FAR “Good Practice Guide for the Trading of Maize Forage”.

Milk Lines


Accumulating tDM/ha and DM%
  • Less than 30% DM
  • Watch and wait
  • 1-2 weeks to reassess DM%

1/2 Milk Line*

Accumulating tDM/ha and DM%
  • 30 to 35% DM
  • Watch closely
  • Within 7-10 days of harvest especially if silage quality a priority
  • Check against:
    • Husk colour
    • Whole plant moisture
  • Chop whole plants for DM% test

2/3 milk line

2/3 milk line*

Accumulating tDM/ha and DM%
  • 35 to 38% DM
  • Check against:
    • Husk colour
    • Whole plant moisture
  • Chop whole plants for DM% test
  • Harvest imminent

Black Line

Black line*

Accumulating tDM/ha and DM%
  • 38% - 40% DM
  • Chop as soon as possible
  • Short theoretical length of chop required
  • Focus on good kernel processing

*Depending on weather and dry down rate, DM can increase by 1% every 2-3 days. 

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