Sunday, September 29, 2013

OK, OK, I'll get a soil test

After seven years of gardening in my current spot, four years of blogging about it, and two years with the Master Gardeners, I'm just now getting around to getting my soil tested.  Why now?  Truth be told, my veggie garden wasn't very productive this year at all. The only crops that produced anything of substance were chard, cantaloupes and Juliet tomatoes. Cucumbers, corn, beans, squash, garlic, potatoes, sweet potatoes and big tomatoes were all a bust.

There's lots of factors to consider when a veggie garden doesn't produce well, including but not limited to soil fertility, the variety of vegetables planted, timing and spacing of crops, pesticide contamination and irrigation.  A soil test can help sort out some of the fertility issues, but not all.  We can't test soil for microbial diversity, for example.

Nitrogen (N), phosphorus (P) and potassium (K), the three major macronutrients in soil, are what most of us think about when we think about fertilizing our veggies and ornamentals.  You'll see N-P-K listed as percentages on labels of commercial fertilizers (10-10-10, 8-2-4).   But there's more to soil fertility than just N-P-K. Micronutrient content, salinity, structure, texture, soil biology and pH all play important roles, too, among other things.  It's complicated!

soil test

Though a soil test won't answer all my questions, it should give me some clues as to what might be going on, and at the very least, end the guessing game of what nutrient might or might not be missing. So, I've decided to test two types of soil in my garden:  the soil in the back yard that's been untouched for about a decade (possibly more) and the soil in the veggie garden beds that I've amended numerous times.  (Not sure why I wrote "Lawn" on that first bag -- it's mostly weeds and horseherb back there!)

To collect the samples, I carefully dug out ten divots of soil from each area, at least six inches down, after scraping the live plant matter off the top.  I mixed the divots together in a clean bucket and removed any visible rocks, weeds, roots, and mulch before bagging the samples.

What's striking to me is how similar the two dry soil samples look.   The unamended soil on the left is a little stickier (due to a higher clay content and less organic matter) and a little grayer in color. Otherwise, I can hardly tell the difference from the amended soil on the right.
soil samples

However, when wet, the difference is clear.  The unamended soil (this time on the right) has the texture of modeling clay, while the amended soil (on the left) is soft and crumbly.
soil clods

Clearly I've improved the soil structure and texture by adding store-bought garden soil, compost, manure, and mulch to my beds once or twice a year for the past seven years. But what about the rest? Time to find out.

More to follow...stay tuned!

Words and photos © 2009-2013 Caroline Homer for "The Shovel-Ready Garden". Unauthorized reproduction is prohibited.


  1. Tha is something I should do too but I would have to send in 20 samples as I have so many different areas. What do you suggest?

    1. To narrow down the number the soil tests, you could test similarly-amended areas together, much like a farmer tests the soil in a vast open field. Even if your areas are separated by walls and host different plant species, if the soil was amended in the same manner, and you're having similar issues in all those spots, I'd test all those areas together as one sample. Take several divots or slices of soil throughout all the areas with the same type soil, mix them all up in a bucket, then send in a 2-3 cup sample of that mixture. Another option: test only those areas where you're having specific problems that suggest a nutrient deficiency (or salinity problem. another factor these labs can test for).

  2. Soil testing has been on my to do list for years. Kudos for getting yours done. You would think as a master gardener I would do this, but still I have not. If it's any consolation, I did not have a particularly good garden this summer either. Productivity was way down and I had bottom end rot on my tomatoes which is pretty unusual. Was it caused by uneven watering or calcium deficiency? I don't know. Yet another good reason for a soil test. Maybe I'll finally get it done.

    1. I've been blaming lots of stuff on the drought but I know gardeners who are getting decent yields. I've been working on organics, timing, spacing and variety selection and all that has helped but I'm still not satisfied. Plus I'm just curious.

  3. When I had my soil tested in my previous garden, I was sorely disappointed... told me squat!
    The extension service recommended chemical fertilizers :(

    There are ph home tests... Those might be worth looking into... In my area, I just figure that the soil is going to be acidic... unless there's been a burn pile... and add the ashes from my fireplace to areas that seem in need of a pick-me-up.

    Good luck with your soil test, with luck, texas will give better recommendations than Georgia.

    Your soil photos are some pretty... Mine would look like beach sand.

    I just googled your soil...
    Appears like you have something called Houston Black... The state soil!
    I would avoid adding ashes... You need to lower the ph...