I plant about 12 acres with Sainfoin, Borage, Crimson clover, Birdsfoot Trefoil, Hubam clover, and a bit of Buckwheat.. That mix works out well, there is always something in the field blooming and the bees take adantage of it..
Having said that.. I make two hundred dollars an Acre cash leasing my land, and thats a bit less than the going rate from neighbors lands.. I cant afford to plant more for the bees at that price..
I think it was Larry Conner that said 5 WELL planted acres could support 20 hives... I keep 20 to 30 hives in my home yard and wanted to make sure, so planted 12 acres..
It requires money to do it.. Round up to burn down what ever is already there, then a good disking to break it all up. A spreader to broadcast the seed, or a Drill to drill the seed. If broadcasting it takes a clod buster or a disk to incorporate the seed, and of course, it takes a tractor and fuel to do all of that, not to mention the cost of the seed mix...
With the mix I mentioned above, I cut it and bale it, and use it for cows and horses, so I can recoup some of the money spent. Otherwise it would not be worth it..
If you try to cheap out and plant with something already standing, most of those cover crops will be crowded out within a couple of years. It will also require mowing more often due to the weeds that will crowd out and shade the desired bee forage.. Oh yeah, did I mention mowing it once or twice a year to keep the weeds down?? You also need to re disk and re plant at 5 or 6 years to keep the optimum forage growing.. at least here, if you dont the Fescue and other grasses will crowd out your preferred growth, even when you do mow it once in a while..
I consider it very worthwhile, my honey crop HAS improved dramatically, and my critters seem to like the mix as hay, and it also sells well as hay. If you have no secondary purpose or income from it, then no, its not worth it, not even close.