Sunday, December 1, 2013

Soil test results

The results of my soil test results are back from the Texas A&M AgriLife Extension Service Soil, Water and Forage Testing Laboratory. I sampled two areas for testing: the veggie garden beds and the back yard soil, six inches down, green material scraped off and discarded.  Here's what the Aggies had to say.

Back yard sample - this is as close to "native" soil as I have, though the native top soil was likely scraped off and fill dirt added when the subdivision was built in the late Sixties. When Jack bought the house in 2004, the "lawn" was a mix of Bermuda, St. Augustine and weeds. Much of the turf has died off, and horse herb and oxalis have moved in. This clay soil has not been amended in a decade.

The soil test results - iron was low. Nitrate and phosphorus were moderate.  Potassium, magnesium, sulfur, zinc and copper were high.  Manganese, boron and calcium were very high, and pH was moderately alkaline at 8.0. Organic matter content was good at 5.89% (despite no added amendments). If I had turf grass growing here, the Aggies would recommend fertilizing with nitrogen and phosphorus three times a year during the growing season, plus foliar iron every 4-6 weeks, particularly if the grass was noticeably yellow.

Veggie garden sample - this soil is mostly Hill Country Garden Soil trucked in from The Natural Gardener, amended yearly since 2009 with Ladybug brand Revitalizer compost, and fertilized spring and fall with Ladybug 8-2-4 fertilizer according to directions on the bag.  I mulched these beds with Sylvan mulch in the spring.  I tested the soil after harvesting summer crops, before doing any fall preparations.

The soil test results - compared to the back yard sample, the nitrate levels were much lower - virtually nil - and the phosphorus levels were much higher: so high, in fact, that the Aggies recommended I add no additional phosphorus for five years before retesting!  Organic matter was about 2% higher than the "native" soil, and pH was a little lower at 7.7, though still in the moderately alkaline range.  All the micronutrients were elevated, including iron; manganese, boron and sulfur were very high. The Aggies recommended only one additive: 1.3 pounds of nitrogen to every 1000 sq ft every 4-6 weeks during growing season (my eight 4' x 6' raised beds total about 200 sq ft).

Finding a fertilizer that contains only nitrogen and nothing else may prove to be a challenge, particularly one that's fast-acting, organic, and reasonably priced!  Blood meal contains iron, while manures, fish products and plant-based "meals" contain 1-4% phosphorus and/or potassium.  But clearly, the soil in my vegetable garden is nutrient-rich and needs no additional phosphorus, potassium or micronutrients.  Planting cover crops and nitrogen-fixing legumes would be another way to boost the nitrogen content of the soil.

Have you ever had your soil tested?  What were your results, and did testing change the way you fertilize?   Leave a comment and share your soil test stories.

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


  1. Crazy - I always claim I'm going to get my garden soil tested (actually I really should get the garden soil tested).

  2. I have been meaning to do this too! thanks for sharing. If you don't plant a lot of your veggies from seed, corn gluten can give you the straight organic nitrogen you are looking for...

  3. I've not ever tested my soil, not in the veggie areas nor the ornamental areas (shrubs, perennials, bulbs,herbs and such). I tend to rough compost anything and everything (weeds/leaves/dead plant material...leave it long enough and the seeds get burnt up), starting new piles in new spots around the edges of the yard, leaving it be for a few years until I think about checking it. By then I usually have black dirt that's really loose and easily worked into whatever garden area is handy. Since the majority of my gardens are ornamental, I've also used piles of semi-composted stuff to start new beds on top of old t-shirts spread out over a new area. I usually start with daylilies and in a year or two move them and put in something else. I seem to be creating more compost than I need some years. A major part of what is in my piles is mower-ground willow oak leaves, a tree very common here in the Carolinas. I usually loose rake them up around the azaleas and then rake the rest into a row, mow it, rake it, mow it again and then rake it into a pile somewhere to sit and do its thing. My veggie garden areas (haphazard to say the least) get this stuff worked in every year. I have learned, however, not to work in too much at a time or the soil is so loose that it has trouble holding water when we have a dry spell. I've actually taken to stealing clay/heavy soil from friends and fields just to make my soil more dense. the fact that my house was built on an area that had been raw and unused, covered in weeds/grass/brambles/leaves and hadn't ever been cleared, means I have no clay in my yard, no imported foreign soil...which also means no fire ants. Long and short of it...just haven't ever worried about getting my soil tested, not as long as what I plant thrives.