Both clover and buckweat are excellent cover crops. Personally, I enjoy growing green manure crops that I can harvest such as bush varieties of peas and beans. They not only cover the ground quickly, but they enrich the soil because they „fix” there own nitrogen. Do not bother planting them in rows, just sow them freely as you would any other cover crop. I guarantee that you will have more than enough produce to go around for you and the neighbors!
Treat that red clover with mycorrhizal fungus to get more bang for the buck in soil benefits. Really brings in the earthworms and they go crazy over clover and alfalfa clippings. Also, if you can, keep things green for as long as possible. Dunno about red clover – but vernal alfalfa has an extremely long growing season, and you can interplant rye grass. Living roots and green cover for as much of the year as possible helps keep microbes and earthworms closer to the surface longer where they can do more work and gives mycorrhizae and family more time to become established. And whatever you do – once you get started – do not disturb the soil. Tilling will destroy a vast majority of the benefits of the young subterranian ecosystem you would otherwise reap. No need to turn the „green manure” – the earthworms and family will do that for you if you’re patient – and do a better job of it. I’m starting my garden off with alfalfa and sudan/sorghum to condition the soil and create next year’s mulch. Sudan/Sorghum will provide much of the surface mulch, alfalfa will break up the soil deep down and introduce organic matter deeper than the few inches of most plants. I’m having problems convincing the wife to let me plant clover or alfalfa in the lawn to jumpstart it – but then, regular lawn grass with my favorite fungus can produce an 18” deep rootzone, so I’m not desperate. The wildflower meadow idea is great – really attracts the insects you want to have around plus helps replenish what we’ve destroyed for grass yards and golf courses…
I’ve used several (annual rye, vetch, clover and field peas). I’ve used them as between-crop filler and over winter. I’ve pretty much settled on Austrian field peas as my favorite. Because of where I live (Stanwood, WA–Zone7-8), hardy annuals can be a pain. We don’t get much cold weather, so „annual” rye never dies back and I end up with something akin to a lawn (unless I plant really sparsely) to turn under. Vetch and clover become a nuisance in short order due to the complexity of their root systems and their tendency to set seed quickly. Field peas, on the other hand, have everything I want in a cover crop. They have shallow roots that form huge (sometimes the size of a golf ball) nitrogen-fixing nodules and they break down quickly in the soil. They grow very quickly and have beautiful purple blooms that make great cut flowers. I think if you live in a colder climate, any of the crops I mentioned would work nicely, though.
I am going to do a little more homework on these but will absolutely try one or two. I’m thinking the red clover in the front area where the soil is so hardpacked & dead and peas or beans in the garden since my neighbor gave me about 20 packets of seeds of each! From what I’ve heard neither one do particularly well here so they’ll be put to good use as cover until I get to planting that part of the garden. I have more or less determined that I’m in zone 8.
I’ve tried crimson clover for two winter seasons now. It isn’t doing what I want for over-winter cover. I’ve tried fall rye, and like Brina said it doesn’t die off here is South Coastal BC. I’m actually going to try the mix Brina alluded to (fall rye, peas, and vetch) this year. I’ve heard that mixing a N fixer with an organic builder gives you a double boost. But I’ve also heard that if you have a wire worm problem, using grass-type green manures will make the problem worse. All that said, crimson clover looks beautiful when it flowers in summer. I’m going to sow some on bare ground this spring just for the flowers. Bees love them. I haven’t used Buckwhet either, but I’m planning on trying it this summer; I’ve heard good things about it as an organic builder. I have seeds for Phacelia, to try this year. If anyone has tried it, please let me know. The description is good organic building, nice smelling flowers, and bees love it.