Corn Silage - Determining When to Harvest

Stuart Carlson, Northern Product Agronomist
August 12, 2020

It's difficult to determine when to harvest corn for silage at the right whole plant moisture.  The optimum whole plant moisture for ensiling varies for each hybrid, environment and type of storage structure.  Harvesting too dry reduces yield, can cause mold to develop, lowers digestibility, reduces protein and vitamins A and E.  Harvesting too wet reduces yield and can cause souring and seepage, which causes lower intake by dairy/beef cattle.  Proper whole plant moisture must be obtained of the ensiling corn for correct fermentation to occur to preserve its quality.

Most guys will use the milk line method to help determine when to cut corn silage.  This is done by breaking an ear in half and visually seeing where the milk line is located on the kernel.  Even though this is not the most reliable method when used alone, it is a good tool to gauge crop progress along with a percent dry matter test when corn is denting.  With these tests results, you can roughly predict the proper timing.  A hybrid selection can make a difference on harvest timing.  Hybrid characteristics such as drought tolerance, disease tolerance, stay green and grain dry down will all effect harvest timing.  Environment will affect whole field timings of harvest.  Soil types, crop rotations, insect pressure and weather events do tend to add variance in whole field variability. Drought has a large effect of timing of harvest and nitrates left in the stalk.  Please refer to Eric’s blog Making a plan for drought-stressed corn silage.

With all that said, there is one more thing to take into consideration: the storage structure itself.  Different structures allow ensilage corn to keep its quality at different moistures.  A properly packed horizontal bunker can take silage with moistures of 65-70% while upright oxygen limiting silos should be filled when the moisture content is between 50-60%.

A rough rule of thumb guideline for milk line stages and different structures to begin checking silage moisture.


Milk line stage

Ideal moisture target

Horizontal Bunker






Upright concrete stave



Upright oxygen limiting




Corn silage is normally cut around 6-8 inches above ground level. Moving the cutting height up 12 inches to 18-20 inches may improve silage quality because the bottom portion of the corn stalk is higher in fiber and lower in digestibility, however, increasing the cutting height lowers tonnage per acre.

While determining moisture content of your corn prior to harvest is difficult, it is very important to spend some time walking your fields, pulling whole plant samples, looking at the ears milk line and evaluating the maturity of the plant to maximize the feed quality and tonnage.

If you have more questions on this topic, please reach out to your local Hoegemeyer product agronomist.


  • Crops, WCM newsletter August 25, 2016