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Soil Test

May 11, 2011

Box provided by soil lab, filled with soil for testing (photo credit: Jean Potuchek) I always feel that creating a new garden area is a lot like painting a room – 90% of success is in the preparation. For the better part of the past year, I have been doing the preparation work for my new Serenity Garden. First, I laid out the boundaries of this new garden area and did a sun study (see Planning the Serenity Garden). Then I created a design plan of suitable (I hope) plants (see The Plan). When I was home in Maine in late April, I took a sample of soil from the new garden area and sent it off to the Maine Soil Testing Service at the University of Maine. The information from this test will tell me just what I need to do to turn my glacial sand into perfect garden soil.

Many gardeners purchase do-it-yourself soil testing kits, but I prefer to send my soil samples off for professional testing. In the United States, soil testing services are usually provided at reasonable cost by the land grant state universities (do a browser search for “soil test” plus your state’s name to find information), and the results come with a set of specific instructions for amending the soil to correct any problems.

In Maine, the University of Maine Cooperative Extension Service provides both instructions on taking a soil sample and handy little boxes for mailing the soil sample off to the lab. The instructions recommend mixing samples from at least 15 different parts of the field to be tested, but that seemed a bit excessive for my 120 square foot flower bed. Nevertheless, I dug several holes dotted around the planned garden area by pushing away the pine needles that cover this area and using a trowel to dig out a plug of soil about 8” deep. I mixed the soil from all my holes together in a bucket and then filled the box from that mixture.

One of several holes from which soil was taken for soil test (photo credit: Jean Potuchek) Soil from the various holes was mixed together in this bucket (photo credit: Jean Potuchek)
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The box was sent off with a form providing information about how the garden area would be used and a check for $15 to cover the cost of testing.

Yesterday, I received my results. As you can see below, the report includes both a table showing the conditions of my soil and a set of recommendations for amending the soil. Soil test summary (screen shot)

The low pH of the soil is typical for my property and hardly a surprise in this area at the edge of the woods where decades worth of pine needles have dropped and decomposed. Although the proportion of organic matter is also low, it is actually higher than is typical for my property, which means that I won’t need to add as much manure and compost as I usually do.  A separate sheet of information on managing micronutrients that came with my soil test report tells me not to worry about these; if I get the pH right, they will take care of themselves. There are also additional pamphlets and information sheets about how to interpret my results that are easily available from the soil lab website.

Soil amendment recommendations (screen shot)

The recommendations for soil amendments are designed for farmers planting fields of crops, so they need some adjustment and interpretation for my flower beds. Since the amounts are per 1000 sq. ft. of field, and the Serenity Garden will be a little over 100 sq. ft., I can simply divide the recommended quantities by 10 and round up a little. The first thing I notice when I read these recommendations is that I can get the both the potassium and the pH in my soil up to optimum levels by adding about 10 lbs. of wood ash. Since I heat my house with wood, this is a soil amendment that I always have readily at hand! I’m less sure how to interpret the results about adding manure; these seem to assume that I have access to raw manure from a local farmer (or my own farm animals), but I’m planning to use bags of composted manure from the garden center. Happily, my report came with the email address of a soil analyst who can answer any questions I have, so I will ask how to convert bushels of raw manure into bags of composted manure. While I’m at it, I’ll ask how much the addition of composted manure and compost should reduce the amendments for nitrogen and phosphorus.

I usually dig new flower beds in 6 square foot sections (see Garden Alchemy), and there will be 20 such sections in this flower bed. So once I have determined the appropriate amounts of each soil amendment, I’ll divide that amount by 20 and that is how much I’ll add to each section.

Many gardeners have success with a more intuitive, seat-of-the-pants approach to soil preparation, but I’m most comfortable with data-driven decisions. I love having numbers based on scientific testing that I can put into a formula to create the perfect home for my new plants. Soon, I’ll be able to put that information to use as I actually start digging this new flower bed.

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18 Comments leave one →
  1. May 11, 2011 10:32 pm

    ph 5.2!? I would kill for acid soil. So much nicer than alkaline, but we take what we’re given and put the rest in grow boxes.

    • May 13, 2011 11:01 pm

      Susan, If you want acid soil, all you need to do is move to Maine! There may be someone somewhere in the state with alkaline soil, but I’ve never met such a person. One reference on soil pH that I was reading said that once you get below 5.5, nothing will grow in it except blueberries. And, indeed, blueberries are one of Maine’s most famous (and most delicious!) agricultural products. Whenever any patch of ground at the edge of my woods gets enough sunlight, blueberries grow there (but I never get any of them because the wild turkeys eat them before they are quite ripe).

  2. May 12, 2011 7:36 am

    How very interesting! I actually looked into where I could send my soil off for results, but stopped there. I really should carry through, especially since our house foundation is limestone. This is a very inspiring reminder. I look forward to seeing your soil transform into your serenity garden.

  3. May 12, 2011 7:37 am

    Jean you are such a good role model for me. I need to stop, think and plan more with my gardens. Always seeming in a hurry I rush too much. With the veggies I have had to slow down much more. I know we have a service like that here. I think I may need to do a bit more investigating with my soil. Although I know it is clay and alkaline, there is such much more info they give you in the report. Thx Jean

    • May 13, 2011 11:11 pm

      Kathy and Donna, Aren’t you both in New York? I think your soil testing service is provided by Cornell (http://soilhealth.cals.cornell.edu/). Their basic service is more expensive than Maine ($45), but it also seems to include more kinds of information.

  4. May 12, 2011 8:40 am

    Jean, I am very impressed with your thoughtful approach to creating a new bed. and I’m sure I will be very impressed when this bed starts to grow. I’m very much, seat of your pants, dump stuff in kind of gal so this is a revelation to me. Wish wish wish (for the millionth time) that Canada had such a sophisticated program as Americans when it comes to extension offices and soil testing. Having someone to call when needing help sounds like an absolute gift.

  5. May 12, 2011 4:23 pm

    Jean, like Marguerite, I’m very impressed with your approach to creating your new bed. It’s always so tempting to rush out and buy lovely plants as soon as you’ve identified somewhere to put them (or even before you have!) – but you demonstrate so well the advantages of playing it long. I look forward to reading about the next stage in your plan.

  6. May 12, 2011 8:29 pm

    You will be happy to know that I always recommend that my customers send a soil sample to Penn State for testing. You probably won’t be surprised to find out that I never test my own soil but just add compost. Do as I say not as I do would be the motto here.

    • May 13, 2011 11:26 pm

      Jill and Carolyn, My deliberative approach to gardening is mostly a virtue born of necessity. I have what may be the world’s worst soil. When I first bought my house 20 years ago, a friend who is a plant ecologist came to visit. She looked out at the front yard in summer, asked me again when the house had been built, and said, “Wow; 15 years since the soil was disturbed and all that has grown back is moss! That’s really bad soil!” I don’t test every new area of the garden. When I dug the fence border, for example, I assumed the conditions were the same as the nearby deck and blue & yellow borders and used the same “formula” for amending the soil. But the conditions in this area at the edge of the woods are sufficiently different that a test seemed in order. I’ve also learned the hard way that my attempts at intuitive gardening are often unsuccessful. Early on here, I used to layer wood ash and oak leaves with food wastes in my compost, figuring the acidic oak leaves would balance out the alkaline wood ash. Wrong! When I sent a soil sample from a part of the garden where my plants kept dying, it came back as much too alkaline. Since Maine soil is so acidic, the soil lab folks had my number; the soil report came back with this stern admonishment: Stop using wood ash!

  7. May 13, 2011 6:31 am

    How intriguing! I’ll have to look in to whether something similar exists in the UK, I can certainly see the value in it when planting a new area – or moving to a new garden.

    • May 13, 2011 11:30 pm

      Janet, I did a quick search to see if I could find anything similar in the UK, but all I came up with was commercial soil labs (which seemed mostly set up for commercial farming operations) and diy kits. In the United States, the services are usually provided by the land grant universities, which were set up with (on land donated by the federal government) with the mission of providing a scientific basis for agriculture. If there are institutions of higher education in the UK that specialize in the study of agriculture, hortiulture, forestry, etc. these might be the places to look for a similar service.

  8. May 13, 2011 3:00 pm

    Fifteen bucks for a personalized soil test sounds like a terrific deal. I have corners of the garden where nothing seems to grow, and I think a soil test would be a great idea for those spots. I’d guess the results would have to be taken with a grain of salt, depending on what you intend to plant in the beds. I’m sure your nearby woods with similar soil are supporting a thriving community suited to your particular soil conditions.

    • May 13, 2011 11:35 pm

      James, It is a terrific deal! And if you’re willing to take your samples and get them sent in during the off season, there’s a discount. The form that you submit with your sample actually allows you to specify what you will be growing on the sampled soil so that they can tailor the recommendations to the “crop.” They also allow you to specify some things, like the pH range you are trying to attain. For home gardens, they assume that the desirable pH is 6.5 and that’s what the recommendations are set to. But if I were planning a garden area for particularly acid-loving plants or particularly lime-loving plants, I could ask for a different target pH. Actually, because the pH in this area is so low, there is surprisingly little growing there. (I don’t think it gets quite enough sun to support blueberries.)

  9. May 14, 2011 5:57 am

    (Hopeful noises – might you mentor a new Blotanist? The initial interest has waned and I am sorry for the Blotanists in waiting)

    Was amused while blogspot was down by the Twitter furore, and then when blogspot came back, the enthusiastic response knocked Twitter down ;~(0)

  10. May 16, 2011 10:40 am

    Great post! I’m so impressed with your rigor. I was recently interviewing soil scientists on the proper way to take a soil test, and your version is spot on what they recommended. This is a great description.

    I took a soil test once in a garden I had gardened in for years. The results explained so many of the frustrations and surprises I had with certain plants. Now, it’s the first thing I do.

    Well done!

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