California Gardening Soil, Compost & Mulch

Is there a silt layer at all in my soil test?

3 years ago

Sonoma County, California here. I have been double-digging and amending all new flower beds all summer, and it has been back-breaking and takes forever. I decided to do a soil test. I assumed I had adobe soil which is common here, but the soil actually drains okay -- it's just super hard and compacted and also filled with rocks.

I wanted to be sure I shouldn't be adding sharp sand since I'm working so hard here, by hand, one square foot at a time, adding about 50% compost. Mainly I am amending it because it is so impossible to dig. Also, I'll be planting some bulbs soon.

So I did some mason jar soil tests, and the results 48-hours later don't show three layers? I see two, but I'm not sure? I marked the first one after a few minutes and figure that's sand. Should I let it sit for longer since the water is still cloudy? And is there a silt layer in here, or is it really just sand and clay?

Makes sense that it has more sand than I'd have thought. I live about 25 miles inland from the coast, and like I said, the soil drains better than you'd expect for clay (even in a foot deep hole, water doesn't sit for more than a few minutes).

But trying to figure out if I'm interpreting this right.

We do have adobe clay soil in this area, a.k.a. "heavy clay" which is used to make bricks, but not everywhere in the area. Maybe it is in my yard though. And if so, should I be adding anything more than 50% compost? Like perlite? I don't think there is a massive drainage problem, but maybe that's because of the huge number of rocks and pebbles. I just want my future gardening to be a lot easier than it was this year!

Here is the soil sample.

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Comments (4)

User
3 years ago
Did you check the jar after 2 hours or so? That would be the silt (2 minutes being the sand).

And at this point, the test is done. The little bit of cloudy that's left is not worth worrying overmuch about.

That second somewhat-broken layer might be silt, it's hard to say. Assuming it is, I'd off-the-cuff estimate about 20% sand, 10% silt, 70% clay. Give or take some given the curvy nature of the jar, irregular lines, and the fact that estimates are close enough anyway.

That's actually not a bad place to be anyway. A good clay soil can hold a ton of resources, lots of water, and grow wonderful plants. But it needs the right calcium to magnesium balance or it can be tight and nasty, and needs to be properly aerated and have good organic matter levels and lots of happy bacteria and worms and whatnot to keep it open and properly drained.

Lacking that, it can be a dead, ill-draining mess...
Sara B.
Original Author
3 years ago
Yes, it's growing roses, hollyhocks, tomatoes, cucumbers, dahlias, really well, so I know it's alright. And it does retain water, which is good when it's hot. It's just a bear to dig and amend this year for more variety of flowers. I heard we had heavy clay soil here but thought my eyes were deceiving me. I guess not.

It seems to drain, which is why I thought perhaps it wasn't clay and did the test. I was trying to decide if I should cut with sharp sand or something liker perlite or vermiculite. Seems like it has a fair shake of sand in it already, which must be why it doesn't flood up when it rains.

I probably could add more worms. I've only seen a few, ever, even when getting far down.

I did check it at 2 minutes, 2 hours, a few more hours, and I marked a spot where there was sand at 2 mins. I never saw another layer after that and was confused, thinking it had to have some loam in it at least.

Appreciate the 2nd set of eyes.
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armoured
3 years ago
I would not add sand as in some circumstances can make it even harder. Likewise, "adding worms" is not really viable, worms need the environment to be right, and adding them if the conditions isn't right won't do much of anything. (Assuming there are any at all in there, which it sounds like there are some).

Just keep adding more organic matter - compost, most organic mulches, wood chips, leaves, whatever. In the normal process of a soil with decomposing stuff, some of the clay will 'agglomerate' with partially decomposed materials. Note that you want at least some of the organic matter you add to be a bit harder to break down - usually meaning at least a bit of woody content (lignin) - although you probably don't have to make any special effort for that, most compost will have some, unless it was originally composed entirely of e.g. really soft fruity stuff. Since you're in a pretty warm climate where composting can be pretty quick, you may just have to keep adding.
User
3 years ago
All that and a bag of chips. If the bag is made of paper, throw that in there as well. :-) If you get fall leaves, those are great. Grind them up and use them as mulch. Don't dig them in, they suck nitrogen as they decay. Everything should be top mulched.

Over time, your existing worms will reproduce. Like mad. I have a 95% silt soil that used to be pretty dead. Nowadays, it's full of organics and worms, but it did take many years to get it there. And many, many, many applications of material. I've imported neighbors' leaves from properties I know are good (either no herbicides or ones I'm comfortable with, as I have flower gardens), on an "I rake/blow them, but I keep them" deal. I've imported my mother's leaves, same deal.

I feed the gardens organically using grains (mostly soy) split with urea nitrogen for faster development since PA has a short growing season.

Is there a silt layer at all in my soil test?

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Sara B.
Original Author

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Is there a silt layer at all in my soil test?

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Sara B.Original Author

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armoured

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Sara B.
Original Author