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I have some garden soil that has decaying spruce needles mixed through it. What should I do to the soil in order to grow vegetables in it normally?

  • is there much growing there now? I know they tend to be a good way of keeping unwanted growth out. – winwaed Sep 18 '11 at 2:24
  • @jmusser Have a lot of needles fallen off? Has the spruce recently been through stressful conditions ie Excessive heat, drought? Is the spruce showing any of signs of stress? Would it possible to post one or two photos? – Mike Perry Sep 18 '11 at 15:33
  • Actually, the needles were composting in a pile next to the garden and a neighbors dog dug them in. The plants there are thin and yellowish and don't produce well. – J. Musser Sep 19 '11 at 1:30
  • @jmusser "The plants there are thin and yellowish and don't produce well" is that statement in reference to the Spruce trees? If yes, could you you please post a photo or two showing the trees... – Mike Perry Sep 19 '11 at 19:49
  • The trees are somewhere else, and are doing okay. The plants there are garden plants. – J. Musser Sep 20 '11 at 1:49
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Suspect over-acidity... check the pH and add lime if needed. Is the soil good otherwise? Spruces (at least around here in New Hampshire) are often in pretty sterile soil that needs amending with other, sweeter organic material, like composted manure or other compost.

When there's too much uncomposted "brown stuff" (leaves, etc.) in the soil, it will rob nitrogen in order to digest all the carbon. So consider adding nitrogen one way or another.

If the dog has also been urinating in the area a lot, it can mess up the soil. Apply gypsum for that.

Does the soil drain well? Is there hard pan underneath it?

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  • The soil is clay base and normally fertile. – J. Musser Sep 19 '11 at 1:33
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Two potential problems:

  • Spruce (and other conifer) needles are acidic, and having them mixed into the garden will make your soil acidic. If your soil pH is too low (acidic), vegetables will have a hard time taking up the nutrients they need. This can cause the yellowing you mentioned in a comment. You can get a pH test kit at your local garden center.

  • At a 48:1 C:N ratio, spruce needles are somewhat high carbon, and they're small, so they have a relatively large surface area. If you have a large amount in your soil, the microbes that will break down the needles will "steal" nitrogen to do their job. If your vegetables aren't getting enough nitrogen, they will turn yellow.

To fix these problems:

  • Following a pH test, add lime in the recommended amount to bring the pH up to about 6.0-6.5 (this is good for many common vegetables).
  • Add nitrogen.
    • Short term: dried blood or poultry manure are fast acting, organic sources of nitrogen. If you're buying bagged products, read the label and follow directions for how much to apply. If you've got a ton of needles in the soil, use the "heavy feeding" directions, and if it's not that much use the "light feeding directions". If in doubt, follow the light feeding directions, wait two weeks and reapply if needed.
    • Longer term: if you build up the organic matter content of your soil, you'll have a reserve of nitrogen so that you don't need to rely so much on short term additions. To do this, add about 1" of compost or well rotted manure and dig it into the top 4-8" of soil (the deeper the better). In subsequent years, when you've built up the organic matter and vegetables are growing well, you can back this off to ½" or so.

You didn't mention whether this is an existing garden that's had vegetables growing in it successfully prior to being sabotaged by the neighbors dog. If it is new, I'd recommend getting a professional soil test done (nutrient, pH, and organic matter %). It should cost around $15; if you're in the US your county extension office will be able to tell you how to take a sample and where to send it. The test results will tell you how much lime you need as well as how much and what kind of fertilizer to add.

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  • It is an old patch. I have a 4-way soil analyzer that doesn't need batteries. It read the Ph as 2.5 and the fertilizer level as medium. – J. Musser Sep 21 '11 at 1:13
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    @jmusser: It appears that your pH meter needs calibration or is broken. It is unlikely any soil that supports plant life has a pH of 2.5. A very acidic soil is in the range of 3.5 to 4.5. Most pine forests have a soil pH between 4.5 and 5.5. (Note that pH is a logarithmic scale so 2.5 is 100 times more acidic than 3.5.) – Eric Nitardy Sep 21 '11 at 1:27
  • @jmusser: Oops! I meant to say "Note that pH is a logarithmic scale so 2.5 is 10 times more acidic than 3.5." – Eric Nitardy Sep 21 '11 at 2:00
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    I agree with Eric -- pH of 2.5 is in the realm of vinegar. Nothing would grow! – bstpierre Sep 21 '11 at 2:36

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