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I want to plant blackberries, raspberries, and a vegetable garden in the heavy clay soil in my backyard. So, I plan to heavily amend it by spreading 3" expanded shale and 6" of compost and working that 12" or more down by double digging.

Since I don't know this soil's history, I think a soil test is a good idea so I can learn what other deficiencies I need to correct via fertilizer or pH adjustments. Should I send in soil samples before or after I amend the soil? And if after, how long do I need to wait after mixing all the soil up?

I don't think it matters for this question, but I live in a suburban house around Dallas. Zone 8a.

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In this case, because you already decided what you will put down, if you don't want to do two tests, test after. The reason? You will know what your soils current condition is, whether you need to apply lime, and what the nutrient concentrations are. All this is outdated when you add that big of a load of amendments. Also, if you mix them in properly, you will not have to wait before testing, but you will get a more accurate reading if you take several samples from throughout the garden.

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I disagree. I think before is essential because, based on the results, that is how you should decide to amend the soil. If you you want to test after you can get a cheap soil test from rapid test for 5 or 6 bucks. Or buy 40 tests for 15-20 bucks. Your soil test sent into the lab should give you a detailed fertilizer recommendation and let you know pH and organic content. If you add before you test how are you going to know what your soil needs.

I just tested mine (waiting for lab results) but I also did a soil test by rapid test. The results showed high nitrogen and very low phosphorus and very low potassium. What if I added more nitrogen? That would have been a big mistake.

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    He was asking whether he should test before or after amending, for fertilizer/pH adjustments. The amendments he listed are safe to add to the soil in any condition, and testing afterwards will give you a better answer for what that soil needs nutrition and pH wise. – J. Musser Nov 20 '14 at 19:02
  • Also if you test before you can add all amendments at the time of double digging. If you test after amending and find you need something you might want to do the work again. – That Idiot Nov 30 '14 at 20:29

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