I’ve planted some this year to try to see if it’s an easy / lazy way to improve a bit of ground that is compacted from being walked on and not dug over. The advantages are that buckwheat is not in a common plant group, (related to rhubarb), so there are no issues with rotation and it’s quick growing apparently so hopefully I can get 3 crops in one year if you cut it down before it fully goes to seed.
I found it because I was looking for a deep rooted green manure but when researching it more I came across
https://sarep.ucdavis.edu/covercrop/buckwheat which said, “Buckwheat is termed a deep rooter by Pears et al. (1989), but this is apparently an error (Bugg, pers. obs.). Rooting system is superficial but does show a high root volume in the upper soil stratum (0.0-0.25 m in depth) (Bugg, pers. comm.)”. This fits in with other comments about it being easy to pull up. So I don't actually think it is deep rooted, although since I only have 30cm or so down to clay it probably isn't a problem for me.
I just dug over the top few inches of soil and scattered the seed on the surface at around 6-8g / m2 and kept it damp by watering every day. I planted mine back on 17th April. I covered over part of it as we were having cold nights and some started to germinate after 4 days but most took longer probably because of the cold. The seeds are now about 1” high. The section which was not covered is just starting to germinate now.
Senior Gardening: Growing a Buckwheat Smother/Cover Crop “Buckwheat for green manure should be cut and turned under around a week after it begins blooming in force (not just a bloom here and there). When it begins to put its energy into maturing seed, it has slowed producing the lush, green organic matter one wants to improve the soil.”
At that point I will have to see how loose the ground is compared to planting phacelia and if still compacted will try planting phacelia next, otherwise I will dig in the buckwheat which should be easier if the soil have been loosened and plant another crop of buckwheat hopefully to fit 3 in the year.