Downsides to the Deep Compost Mulch System (DCM)
The system that we have been relying on heavily—and enjoying—for the last year has been the deep mulch compost system as described in this article.
Every no-till system has its pros and cons, just as every method of farming does, ever. There is no perfect method out there, there is only the best system for your context. But, as it pertains to our farm, the cons are con-enough to take some time to really examine them. If this is the system you are leaning towards, you can be prepared. To know what you’re possibly getting yourself into should you go this route.
The video below is an overview (and frankly, a visual accompaniment), so check that out, first. I’ve added some extra downsides and expanded on some of those I mentioned. Farmer Jackson is going to share a few thoughts on some of these, as well.
Refresher of The Pros
I’m not going to dive into all of the pros here like we did in our deep mulch article, that’s not what this post is about. Essentially, deep compost mulch is great for heating soil, suppressing weeds, adding organic matter, adding microbial habitat, preserving moisture, and just keeping the soil covered. Instead, I want to really focus on the negatives—or more appropriately challenges—and how to combat or prepare for them. Is “want” the right word? Because at NTG, we feel like it’s our duty. The pros are so-pro, it’s worth the effort to figure out how, exactly, to deep compost mulch better.
It is hard to say if it’s the woodchips or the woody compost that attracts slugs on our farm, but it is not uncommon to wind up with an increase in slug population. Cool, moist soil and tender greens are essentially begging for them. To combat slugs (which I should say, don’t seem particularly damaging beyond the spread of disease and the ick factor, but should be countered because you do not want to give a customer a slug in an otherwise beautiful head of lettuce), there are a few things you can do. The only effective one that I’ve come across is pint containers with some beer in them left around the effected areas. Harvest time is a little early for a cold one, but if you scout them, well, it’s your job (just don’t finish it before you leave some for the slugs, or you’ll have to open another). Slugs crawl in and die a besotted death. Note: when I am old, I would like this same send-off. Thanks. As an added precaution for those you miss, make sure to add a small amount of salt to your wash bins. This will not affect the greens, but will help release the slugs. Then be super diligent about removing them. Like, super diligent.
In drier regions, erosion may not be as much of a concern. However, piling a bunch of compost on top of your no-till beds and expecting it to stay put if you average several inches of rain or more most every month is probably not the best approach (voice of experience). To counter erosion, get it planted and keep it planted as much as humanly possible (one of the four principles of no-till). Roots help keep the compost in place. Perhaps firming it with a roller before-hand would be helpful, as well. The slope of your garden should also be considered. If it’s sloped between 2% and 5% the beds should go downhill, not across it.
Farmer Jackson: Here in KY, our soils can be extremely clay heavy. After removing tarps to initially build beds, even after broadforking, the surface of the soil can still be a bit impermeable between forks. This causes the rain to “slide out” from under the compost, taking it into the aisles. We tried using the tilther to break up the surface compaction, but it just isn’t strong enough for that job in our heavy soil (we mostly use it to mix amendments into the compost layer). Though we are working to move away from even the BCS, using the power-harrow on initial bed prep is essential to keeping the compost in in the bed. Here’s how we are doing it now: once before adding compost to break the surface compaction and add minerals, then once after as a heavy roller to “tamp down” the compost. It’s a lot of work, but we hope to offset it by moving to the tilther for the rest of the season. Jury is still out…
Some of us will only have access to mulchy, low nitrogen compost ::raises hand::, and that’s fine so long as you consider that the compost itself won’t hold as much moisture in it as it will hold below it. When you direct seed a crop, the seeds will not hit a perfectly moist zone if your compost is deep. So, constant moisture must be present until the plant has formed some leaves. This can be a long, hard-fought endeavor with crops like carrots. I also recommend covering it with row cover while germinating. The trade-off is fewer to no weeds, so in that way it’s worth it, but you can also wind up with no weeds and crappy germination. #shrugemoji
Farmer Jackson: Seconded. JM brought up the deep compost mulch trade-off with carrots in his episode of the podcast. He waters up to four intervals a day to ensure germination (do not attempt without a timer). We don’t do a ton of direct seeding on our farm (carrots, radish, turnip, arugula, baby kale, that may be it). But, when we do, we soak it in with a hose just after seeding, cover it with row cover, and may soak it once more two or three days later until we rely on the overhead. DO NOT rely on drip for germination or young direct seeded crops in deep compost mulch. If I hear myself say “deep compost mulch” again I’m going to… let’s just refer to it as “DCM” from now on.
Bed Set-up is Labor Intensive
Starting new DCM beds is a more-than-fair amount of work. Each bed receives roughly 9 barrows of compost to start (so around 1 to 1.5 yards of compost, depending on if the bed has been heavily composted in the past couple years). That’s just a lot of shoveling, walking, dumping, and raking. Then, repeat. Any of those steps you can make more ergonomic, do so, because it’s a big big job for one person. There are a number of drop spreaders you can find to work with little modification, or you can build your own kickass self-loading tractor mount like Broadfork Farm.
Initial bed set up, depending on the quality of compost you receive, is going to require some upfront capital or some great neighbors who have been stock piling their animal manure for years and want to haul it to you for free (not the voice of experience in this one, unfortunately). I like to estimate at least 1.5 years per 100ft bed. So, at $30 per yard delivered for ours, your initial bed prep may cost $45 per bed. Remember, you will not be adding that every year, it will be half and potentially decrease over time (if you want it to) after that initial prep. Something to keep in mind.
I am not going to go too deep here because one of our five-star forum members, David Blanchard, goes into it over at our community. However, phosphorous is a concern in composts that are derived from animal matter. It can be very high and, when applied to soil, the excess phosphorous can lock up other nutrients and prevent fungal growth, among other things. Check it out if that’s a concern.
Mulch in Greens
This is perhaps a little nit-picky, but I get a lot of our mulchy compost inside of our lettuce greens. From covering and uncovering, from stepping over beds, from my four-year-old, seemingly for no reason at all. The mulch washes out easily enough, but being carbonaceous in nature means that when I wash the greens (which sometimes I have to do even when I don’t need to because of the mulch), it floats to the surface making it harder to extract. A finer compost would remedy it. A finer compost would also be very expensive on our scale.
Farmer Jackson: One solution would be to use a landscape fabric. We’ve done so before, it keeps the lettuce amazingly clean even after a deluge, but one of our biggest reasons for tarping and DCM was to move away from dragging all of that fabric around the field. It’s tough to cultivate around the edges, I don’t enjoy installing/removing it, we don’t enjoy looking at it, and I don’t want to leave a bunch of little tetanus shots waiting to happen around the field (rusty 6” sod staples) because my kids often run barefoot around the farm. That said, it could also address the erosion issue.
I Still Love my System
Just because we’re highlighting the downsides does not mean we don’t love it. I just think it’s important for anyone thinking about DCM to understand the potential downsides so they can prepare for them. Notably, of the systems I have trialed, the deep compost mulch is my favorite for the sheer lack of time I have to spend cultivating. Especially for the carrots. My God. Most of my time is spent planting or harvesting, and with the beds I have already set up, bed prep is only a ten minute ordeal depending on what is coming out and what is going in. My biggest weed is almost always the previous crop, which sometimes just means I get a bonus carrot to eat while I work. #bonuscarrot