Oklahoma Alfalfa
Oklahoma Cooperative Extension Service
Oklahoma Agricultural Experiment Station

Every year a few alfalfa producers plant in mid August and get some nice rains.  By mid October they are tempted to cut or graze the new stands.  Generally this is not worth the risk.  Young alfalfa plants need time to develop root systems. Producers should not abuse young stands by harvesting or grazing too soon after planting.  

Being a deep-rooted plant, alfalfa has an advantage of tapping deep moisture supplies, not available to most other forages. Harvesting new stands too early slows development of the root system.  

In fall it may be tempting to graze or cut "rabbit hay" from a new stand.  Either practice can decrease long-term productivity of alfalfa. Most productive stands of alfalfa are generally sown in fall and harvested about May 1 the following year.  

One exception to this generalization would be grazing weedy fields after a killing freeze (lower than 20F). This facilitates removal of weedy grasses that harm alfalfa by shading. If weeds are not controlled with herbicides in fall and are "out-growing" or shading alfalfa plants, grazing during winter is an effective way to remove them. In these situations, grazing is less damaging than shading by weeds.  
The first flush of spring growth on first-year plants does not normally bloom. Harvest should be timed to precede new growth initiated from crowns. If a severe infestation of weeds exists, then first harvest should be taken when weeds become tall enough to shade alfalfa seedlings (normally in mid-April, with cheat). After the first cutting, alfalfa can be managed as a mature stand.  

The Bottom Line: Harvesting fall-sown alfalfa before spring is a risk. If forage is needed, buy it! It does not make good sense to risk the $150 pre acre, or so, spent on stand establishment for a relatively small amount of forage.