Tuesday’s Tips — Soil Testing

Mary Beth and I decided to have our soil tested a few weeks ago. We were curious to know if all the work we’ve been putting into improving the soil over the past few years would show up in the test results. The bottom line is: of course the addition of all those organic amendments, mulches and fertilizers made a difference. We could have guessed that because our plants are happy, healthy and provide an abundance of flowers and crops, but we also wanted to know if there might be any problems cropping up or if we’re about to overdo it with fertilizer.

Mary Beth has been improving her soil for more than 12 years. All of her new beds get a generous addition of organic matter, she mulches often, and fertilizes every spring and fall with her favorite product, Yum Yum Mix. I, on the other hand, got a later start and have only been at it for a little over two years. I also dig organic matter into all my new beds and side dress plants with my own organic compost at least once a year, but I haven’t been so great about mulching.

We had our soil tested at two different labs just to see what the differences might be. Mary Beth sent her sample to the Colorado State University Soil, Water and Plant Testing Lab. She used the Horticultural Applications for Gardeners test which costs $28. I used the University of Massachusetts Soil and Plant Testing Lab. They charge $15 for a Standard Soil Test w/Organic Matter.

Here are the two reports: MB Soil Test and BW Soil Test. They both have their plusses and minuses. The CSU report is well-organized and presented in an easy-to-read chart. The U Mass report is visually a little bit of a mess — clearly this is a report that is based on a format used for scientists not home gardeners, but if you give it a good look it contains a more detailed analysis. It also reports the lead levels in the soil, so this is a test we would recommend for urban and suburban gardens if you plan on growing food crops.

We both live in the West in areas where the soil pH tends to be alkaline. Most plants do best when the pH is slightly acidic to neutral, somewhere between 5.5 and 7.5, though acid loving plants like azaleas and camellias like a soil pH of  5.0. Both of our soil samples tested in the acceptable range for all but acid-loving plants. The U Mass report suggests that I use an acid mulch like pine needles for those plants.

The levels of organic matter in our samples reflected our efforts. Mary Beth’s report indicates that her OM is high and they recommend that she maintain it using organic mulch. My soil OM level is “lower than desired for most herbaceous perennials” and the report recommends that I use plants that are adapted to such conditions or improve the humus content with finished (aged) compost. It goes on to make suggestions for both new bed prep: “in early spring incorporate 1 part peat moss into 2 parts soil along with 3 parts of dried blood per cubic yard of soil;” and established beds: “in early spring and early June sidedress with 1.5 cups dried blood per 100 square feet taking care not to damage foliage and water afterwards.” We really liked that the U Mass report provided a remedy that was so specific.

Both reports give the levels of individual nutrients in our soil and U Mass also included two documents that will be very helpful. One is Soil Test Interpretation and the other is Fertilizer Products and Their Properties. Note that this second one provides info for both organic and synthetic fertilizers. I’ve marked the synthetic fertilizers with X’s to indicated that we do not recommend your using them in your garden. There’s also a handy guide showing the capacity of some common household containers. CSU also provides lots of useful information on their site.

Getting your soil tested is a good idea. It’s a very inexpensive way to find out what your garden needs and it will take the guess-work out of deciding what kinds of amendments to use. It will also help you figure out how much fertilizer you need. Mary Beth found out that her nitrogen is very high. This means that she can skip the Yum Yum mix for a while. Too much nitrogen can result in an overgrowth of foliage at the expense of fruiting and more than that can actually harm plants and the environment. My nitrogen is very low, so I’ll be fertilizing with liquid fish emulsion fertilizer (contains nitrogen that is immediately available to plants) and with another longer lasting organic fertilizer on a regular basis until future tests show a better level.

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