How Late Can I Cut Alfalfa

Drew Mizgalski, Precision Agronomy Specialist/Agronomist

This year has provided many challenges – from widespread alfalfa winter kill, to challenging planting conditions and an extended/late season. Compared to an average year, more acres were seeded down due to poor established alfalfa stands and amplified by lower forage inventories.

Now we’re challenged with balancing alfalfa winter survival with harvesting as much forage as we can going into winter. One key component is nutrition – making sure adequate, plant available nutrients are available to the crop. That last application of potash can help give your stand a better chance to make it next year.

Another important consideration is the timing of your last cutting – and can be a little challenging to think about. Traditionally, it is said that the last cut should happen at or around Labor Day. There is actual data that supports this theory, but there is nothing special specifically about the calendar approaching that date – other than historical temperature trends.

We can dive a little deeper into this and look at an excellent article form Dan Undersander from the UW Extension. If we want good winter survival and rapid green up for good yield next year, alfalfa must either:

  1. be cut early enough in the fall to regrow and replenish root/carbohydrates and proteins or,
  2. be cut so late that the alfalfa does not regrow or use any root carbohydrates.

This is then tied to remaining alfalfa growing degree days: [(max daily temp + min daily temp)/2] – 41°
(example: high 68°, low 48° = 17 alfalfa GDD)

The target numbers that coincide with Undersander’s points above are for #1 – 500 GDD and for point #2 – less than 200 GDD – yes, that’s right – we don’t need to wait for a killing frost (24° for alfalfa) to make that final cut! We just need to be certain that we will not accumulate too many heat units before winter is underway.

So, get out your calendar, grab your calculator and pull up your favorite weather / temperature forecasting app or website. If you prefer, look at historical trends / see chart at the bottom of the article.

For further discussion, make sure to contact Northside Elevator’s team of professional agronomists to determine management options that will work best for your operation this autumn!

UW Extension: Late Summer Cutting Management of Alfalfa Alfalfa Germination and Growth

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