Having invested money and time into growing your maize crop, it makes sense to do everything you can to maximise the value and quality of your end product. Harvesting maize too early will lead to a higher than optimum water content, while harvesting too late will result in increased harvesting costs, low palatability and a heightened risk of frost and mould damage.

So when is the sweet spot for harvesting maize? Here’s our guide to harvesting your crop at just the right time.  

When is maize ready to harvest?

The best time to harvest maize differs depending on the variety of maize sown and the geographical location of your site. However, there are a few simple rules of thumb to help you harvest your maize at the optimum time.

The best time to harvest maize is when the cobs have reached their maximum starch yield, have enough moisture to compact easily in the clamp and have a whole plant dry matter (DM) ratio of between 30% and 38%. Depending on the conditions, maize typically dries down at a rate of around 0.5% a day (although less if it’s raining). 

The most accurate method of determining the dry matter of maize is to conduct a simple oven test, which you can learn how to do here, or by sending it to a laboratory for testing.  

Testing the readiness of your maize crop

As well as calculating the dry matter of your maize, there are a couple of simple in-field tests that you can do to assess the maturity of your crop. 

• Thumbnail test 

Peel back the sheath on the cob and use your thumbnail to check the consistency of the kernels. If the maize is ready to harvest, then the kernels at the top will have a similar consistency to soft cheese and the kernels at the bottom will be like hard cheese. The kernels in the middle should be soft enough to just take the imprint of a thumbnail. 

• Milk line test

The other simple test is the milk line test. Just break the cob open halfway down and remove one of the kernels. The milk line is the point at which the yellow, hard and glassy solid starch at the top of the kernel ends and the milky bottom part begins. If the milk line is between a third and half of the way down the kernel and no liquid is released when you press the kernel, then your crop is ready for harvest.     

Importantly, both the thumbnail and milk line tests only provide an indication that harvest time is near. The only sure way to test that the whole plant dry matter of the maize is in the optimum range is to conduct the dry matter oven test or by sending a plant to a laboratory. 

What if you harvest maize at the wrong time?

Harvesting maize too early or too late can be very damaging to your crop.

• Too early – Harvesting maize before it reaches maturity will lead to a loss in yield, with greater water content reducing the starch intake. Although it will compact easily, the high levels of fluids contained in the maize will run from the stack or bunker leading to the loss of valuable sugars. It will also be affected by high acidity and poor palatability.
• Too late – A late harvest will reduce the crop’s quality, with the leaf and stalk increasing in fibre and becoming less digestible. Harvesting costs and field losses will increase and soil will be compacted and damaged. The risk of frost damage will also rise, potentially leading to mould and higher spoilage rates.   

Checking chop length and cutting height

Before harvesting your maize, you should also consider the chop length and cutting height. A longer chop may be more difficult to pack and reduce the crop’s feed value. However, crops that are too short will not have enough structural fibre to maintain the rumen health of cattle. 

The optimum cutting height for maize is 20cm above ground level, while the typical chop length is around 15-20mm. Take a handful of harvested maize and squeeze it to test whether the chop length is right for the moisture level of your crop. The palm of your hand should feel moist. If you can wring water out of the maize, then either increase the chop length or delay the harvest. On the other hand, if the maize is dry and does not stay compressed after squeezing, then you should shorten the chop length.   

The importance of planning

When you’re approaching maize harvesting time, make sure that everyone involved in the harvest knows their responsibilities and make all of the relevant pre-harvest checks. That includes:

• Conducting a pre-harvest dry matter test;
• Checking the optimum chop length;
• Timing the final irrigation so the crop can survive on the moisture in the soil until it is harvested and the field is dry enough to carry machinery;
• Informing your contractor and checking that any machinery and supplies not being provided by the contractor are ready for use.  

All the help you need

At OJ Neil Contracting, we had a great maize harvest this year and helped farmers across the south east to achieve the perfect whole plant dry matter ratio. With our years of experience, we can help you determine the best time for your maize harvest and provide the machinery, resources and expertise to complete the job to the highest standard. 

Find out more about our agricultural contracting services and get in touch to discuss your requirements with our team.