So yesterday while I was pondering why my direct-seeded spinach was looking pathetic and stunted, I remembered a warning I read in a regional gardening book about a little-known but prolific soil-living organism that will reproduce in cultivated ground over several years, finally becoming an issue once populations reach a critical point. They're attracted to decaying organic matter and water, so essentially, the more you build up your soil and keep your garden watered (things we all strive for), the worse they get. They feed on the young root tips of certain garden plants. I had never paid too much attention, because I'd always moved after a few years in one spot, and they'd never become a problem for me. I was even convinced in my head that maybe they're a rural problem and our city soil was rid of them.
Then I bought a house, and this is my 5th year gardening in this spot, and my spinach looked AWFUL. So I decided to check the soil around the spinach. Sure enough, I found about a dozen of these little guys:
Seems that enthusiastically adding compost and organic matter to my garden every year is a recipe for damaging symphylan populations. Also seems that there's no established cure for infested soil, evasion seems to be the main strategy. You can plant bait crops in the bed with your seedlings, like buckwheat - the symphs will eat the buckwheat roots while your seedlings get established. Once they're big enough, you can hoe down the buckwheat and the plants can usually survive some symph predation. You can rotate in solanums, particularly potatoes seem to repel them, but because they're highly mobile (traveling laterally 15-20 feet), I would have to plant my entire backyard garden in potatoes for a year to repel them out. You can grow species that they don't prefer (spinach, broccoli, cauliflower, cabbage, beets, beans and celery seem to be their favorites), but I imagine if have a lot in your soil already they'll eat what's available if their favorites aren't available. You can grow transplants for their favorites, hoping to get them large enough to survive some predation before putting them in the ground (maybe combined with a nearby bait crop). And you can target lower organic matter levels, compact the top of your soil, and try and figure out how to water less. All of which goes counter to conventional gardening wisdom, but in symph territory, apparently you need to consider this.
I tested the soil in all my backyard beds. They all had at least 1 symph in the sample, which doesn't seem to be a population level that causes too much damage, and plants (even broccoli) growing in these beds are doing fine. The spinach bed had a dozen in the one sample I took. I read that finding 4-5 in a sample that size is a problem population. My front yard beds did not have any in the samples I took, at least in the surface layers (my front yard beds are raised 1.5 ft, so it's possible there's a population living lower in the ground, I might have to figure out a way to sample from down under).
I'm a little discouraged, but I think I can come up with a plan to get the population down and help my plants evade them. The regional garden author I mentioned (who has always been 100% right-on with his advice, I wish I'd listened earlier when he warned against blindly adding compost to Pacific Northwest soils!), says the only reliable cure he knows of to wipe out the population back to "baseline" is a multi-year rotation out of vegetables and into unirrigated cover crops that they don't like, which isn't exactly a great solution for urban gardening where I don't have another plot I can garden while I rotate my main garden out.
It's possible I just won't be growing spinach for a while until I can figure this out. Hopefully my broccoli won't be affected. I was still able to grow amazing broccoli as of last year, and so far so good this year. *fingers crossed*