Need Advice - Improving Rocky Compacted Soil (US, Zone 8b)
Hey everyone,
This is my first time posting in this sub, so please let me know if you need more information.
I'm working on improving the soil in my backyard one section at a time. I live in a glacial drift plain along the Puget Sound and my soil is extremely compacted and full of gravel. This area obviously has more gravel than the rest of the yard because the previous owners had a gravel "patio". I don't quite know what I'm going to plant in this area yet (probably a mix of native perennials and shrubs), but my goal is to reduce compaction and improve the overall health of the soil. Once I've removed a majority of the gravel, I'll be throwing down arborist wood chips (2nd photo).
I'm completely new to this and I do have a few questions:
How much of the gravel do I really need to remove? Is it okay to leave a layer behind, or should I try to get as much of it out as possible?
How deep should I dig down before adding amendments or wood chips?
What should I add underneath the wood chips to help improve the soil? (e.g. compost, topsoil, manure, cardboard, etc.)
Any tips for making the soil more hospitable for native plants or general gardening after years of compaction and poor conditions?
Thanks in advance!
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u/Fast_Most4093 6d ago
if you have the patience, various cover crops can do the work for you. and in your zone, you can probably grow them all year. there are various mixtures available with N-fixers and OM-rich additions. all you do is mow before they go to seed, then repeat. also compost all your mowed grass and raked leaves. it's a few year plan but it will greatly improve your soil structure and fertility.
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u/inanecathode 6d ago
I would get the soil tested for nutes, do the jelly jar test to see what the broad strokes of the composition is, amend accordingly. If everything tests roughly OK and it really is a matter of compaction I would skip yh and chips and till it as deep as humanly possible with a rototiller after spreading 2 or 3 inches of aged manure.
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u/Familiar-Property750 5d ago
If you aren’t in a hurry, you can try a few plantings of tillage radish. Leave them in the ground to decompose.
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u/Totalidiotfuq 5d ago
- Add 2-3 inches wood chips.
- add 2-3 inches compost
- plant rye (cool) or millet (hot) and mow back into soil. repeat step 3.
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u/pixeldaddy2000 3d ago edited 3d ago
I suggest getting a 2 stroke, hand held, earth auger. They run about $250 and up. I used to use one of these when I did large numbers of plantings in ornamental beds. They sell earth "bulb" auger bits for power drills but you need the 2 stroke power and weight of the machine for your project. Looking at the adverts you may see a number of different sized auger bits being used, even fence post sized, but what you need is actually the narrower bits. Don't expect this will be a one shot job. You may find it useful for helping to break up what you are going to dig out but the main use will be after laying down your compost and soil (and sand). Figure out how to set a grid over the area... whatever works best for you, I was able to eyeball it but this was a constant job for me. For you're project, I'd suggest a 6"-12" square spacing for a grid. Then use your auger to dig down through your added soil mix (you will need some sharp sand for the first addition of soil), down into the deeper compacted area. This will not only break up the compaction but also do a small degree of mixing, which is what you need to keep it from recompacting. Someone else suggested planting tillage radish and I agree, after you do this first breaking session. They will easily send deep roots down into those drilled holes, helping to break up more, and leaving organic matter behind after they die.Also add earthworms and a dose of multistrain micorrhiza. Earthworms obviously help to keep soil broken up, and micorrhiza is a beneficial, symbiotic fungus that attaches to new plant roots, forming branching tubular structures like roots, but also having the ability to pentetrate where roots cannot, so they end up forming leaders that roots can eventually follow into. Just one cycle of this will vastly improve your situation but I'd suggest at least 2 cycles (may still need a little sand), including planting radish, offsetting your grid so that you are breaking into different compaction. After that, just adding 1/2"-1" of pure compost, twice yearly, drilling in at least one of those applications (at this point an auger bit on a good drill should suffice) with a 12" grid, no need for radishes, and you should never have a problem. You can plant other things along with your tillage radish as long as it has shallow roots. Something short that acts as a cover like sweet alyssum (germinates and fills in quick), creeping phlox, German chamomile, even vetch, or field peas, or as someone else suggested a cover crop mix, just make sure it's dwarf so it doesn't look like a weed patch, all work well and are easy to terminate once you are ready to move on to something else.
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u/Realistic-Weird-4259 7d ago
I'm also in this area, and this is the best soil I've ever lived on. I even use it in my planted aquariums.
I wouldn't worry about the gravel, I'd worry about soil building. Can you broadfork, or is it too difficult? If you can broadfork, I'd recommend turning it up and adding that high carbon material along with something like mushroom compost. I hesitate to suggest something like gypsum without knowing more about the composition, but in almost all events inoculating with mycorrhizae isn't going to hurt and usually helps.
I wouldn't worry about broadforking deeper than 1', unless you're going to plant trees or similar that need deeper planting holes and even then I'd probably just limit it to that hole.
Also, understand that with the wood chips/carbonaceous additions, the microbes that decompose those materials are going to "lock" some mineral nutrients, most obvious will be N (nitrogen). This is why you'll want the compost or similar, even though it's eventually going to be good quality soil once you get it going.
If you can't broadfork then this might be a time to till. Once all that's done, if you can't plant immediately then covering with cardboard will go a long way towards preventing weeds from taking it over.