For Release October 6, 1998

Timing That Last Alfalfa Cutting

by Chuck Otte, County Extension Agent

It has been a crazy weather year! Summer weather clear into fall. Way above normal September temperatures. A foot of rain in late July, then near drought conditions for 6 weeks, then another round of heavy rain, and temperature extremes to match. Now even more rains may make the decision moot. When we have a fall like this and we have good alfalfa growth coming on there is a normal urge to try to get one more cutting off that alfalfa field. The problem is that we don’t know when that first freeze is going to be that will stop the alfalfa growth for the season. If we knew that we’d know when to make that last cutting.

Alfalfa is a perennial crop. In order to make sure that it will survive the winter and come out next spring with good production it has to go into the winter with a full supply of carbohydrates in the root crowns. When an alfalfa field is cut at the proper time the plants will normally have pretty full carbohydrate reserves in the roots. As the plant starts to regrow following the cut the root reserves start to decrease and bottom out about three to four weeks following the cut or at about the time that the first flower buds start to form. The root reserves rebuild rapidly after that.

Maximum root reserves aren’t actually reached until the plant is past flowering and into the full seed stage. When we normally cut, at 1/10 bloom, the plants are at about 85% which is adequate for summer growth and regrowth, and even for going into the winter. Even 65 to 75% of full root reserves would get most plants through most winters if you don’t do it regularly.

The lower the root reserves going into winter dormancy the less the plant has to grow on in the spring. When the plant starts to grow after a cutting or after winter it uses root carbohydrate reserves to produce stems and leaves. The leaves, through photosynthesis, produce food for the plant to grow on or store in the roots. Early on the plant needs more food to grow than the leaves can produce so it has to use root reserves. The plant doesn’t really start producing more food than what it is using to grow until about flower bud development.

If there are adequate root reserves the plant produces excellent growth and you have a good first cutting. If there are not adequate root reserves the plant will grow slower and put on much less growth before it starts to flower. You have less tons of alfalfa to harvest and the alfalfa plant is behind in the race for the rest of the season. Being a less aggressive plant it leaves more bare ground in the field and more opportunity for weeds to move in. Being a less aggressive plant it is weaker and more prone to insect and disease problems through the season.

The worst thing that can happen in the fall is to take off a cutting of alfalfa and about two to three weeks later we have a hard freeze, 20 to 25 degrees, that stops growth for the year sending the plant into winter with less than a "full tank of gas". It is better to go ahead and let that last cutting sit on the field even if it goes clear into the seed production stage. You will have a stronger and healthier stand of alfalfa. After that hard freeze stops growth you can go ahead and harvest what’s out there or fence it and let cattle graze it. You do not want to leave that last growth on all through the winter since those old tall stems are where the alfalfa weevil lays her eggs this fall. You can reduce your weevil problems by removing that growth by haying or grazing after the killing freeze.

Alfalfa is a valuable crop. It’s expensive to get it started, but with proper care and management there’s no reason that it shouldn’t last at least six years. But that’s with proper care and management. For more information on alfalfa management stop by the Extension Office and pick up a copy of the Alfalfa Production Handbook.


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