In my narrow-minded search for fall-planted, low-residue, winterkilled cover crops, I tried growing phacelia a few times to suit this purpose. It did ok, but I found that with good fall growth, it really isn’t low-residue in spring. More on that later. What I want to share here is that once I opened up my eyes a little (and was no longer being paid to look for low-residue, winterkilled cover crops), I finally discovered what the Europeans have known for a long time: phacelia is incredible as a spring-planted cover crop.
It can handle frosts, so it can be seeded early. I seeded this phacelia on May 2 in Maine. Once it has germinated, which I found it did much better in spring than in August, it can handle dry conditions extremely well. It practially didn’t rain the entire month of May here, and you wouldn’t know it from looking at the phacelia during that time. It has incredile, bee-licious flowers. Bumble bees especially love it, but I saw a few honey bees in there, too.
Some folks in Vermont used a SARE grant to look at increasing pollinators and phacelia was one of their flower choices. They actually counted the bees and found that while honeybees prefer buckwheat, bumble bees do indeed prefer phacelia. They have a great video here:
They do, however, raise the possibility that phacelia can serve as a host for tarnished plant bug. Phacelia might be a good trap crop, or it might raise the pest populations.
I also overseeded some phacelia into rows of oats and peas. I was pretty satisfied with how the phacelia seemed to crowd out the weeds in this combination. I probably went a little heavy on the phacelia seeding rate, though.
Now for the bad news (other than the tarnished plant bug). Phacelia is hard to find and can be very expensive. Luckily, because much of it is imported from Europe, I have found that you can get 10 kg bags (22 lb), so you don’t have to go for a full 50 lb bag like many cover crops. At Walnut Creek Seeds, it’s $4/lb and they recommend seeding at 6 lb/acre. I’m actually not sure what my seeding rate was, but I think it was a bit higher than that.
About that fall-planted phacelia– I’ve seen it be a total failure (not enough residual nutrients), and I’ve seen it grow pretty lush. In terms of nutrient capture, we have data that clearly show phacelia does not capture as much N in fall as radish, but it can capture at least 200 lb when there is a lot of residual N. Last year when I seeded it in mid-August, we got a few flowers, though nothing like the spring bloom. With lush fall growth, the spring residue can actually be a bit stemmy. It definitely does not “melt” away like radish or mustard residue. This isn’t necessarily a bad thing- depends on what you want. Despite the stemmy residue, some farmers report that phacelia’s fine root system helps mellow out the surface soil.
I encourage people to try this delightful cover crop. Maybe go in on a bag of seed with some friends. The bees will thank you.