Cheap Soil Testing: How and Why To Do It

One of the best things about writing for this site is that occasionally, other gardeners will write in with their excellent garden tips. This was the case with Kathy Ormiston, a landscape designer and landscape gardener in the San Francisco Bay Area (south bay region).

Kathy was kind enough to share a tip about an extremely inexpensive soil test that she has done via mail from the University of Massachusetts.

How cheap is cheap?

Fifteen. Dollars. Seriously, people, if you get a soil test, and find out that you’re cool on phosphorus for a few years or that the reason your such-and-such keeps keeling is that your pH is all wonky, then you just saved the cost of the test.

Here’s how soil testing works:

You decide which areas you’d like to test. Sunny and shady areas deserve separate tests, and sloping areas can have different values than flat spots. If you’ve been gardening for a bit, you probably have an idea of whether your soil varies a lot in different areas. You’ll want a new soil test for each distinct type of soil you suspect you have.

For each area, you’ll want to collect 10-12 vertical slices of soil from random spots within that area, using a (clean) trowel/ soil knife and a (clean) bucket to hold your samples. Slices should be as deep as the roots for whatever you’re trying to grow – if in doubt, just go 6-8″ deep for garden beds and 3-4″ for lawn areas. Try not to collect leafy bits or lawn chunks.

Mix together all those soil samples really good, then pull out about one cup of your soil mixture, and spread it on a piece of paper to dry. When it’s dry, pop it in a ziploc, label it (“south bed” or “shady slope”), and mail it off to those fine folks out in MA with a check and their happy little form all filled out so they know what you want.

Then you wait patiently for a week or two, and they’ll email, fax, or snail mail your results to you with some tips about what to do. Here are some of the results Kathy got for her own home garden:


But why bother with soil testing?

l Overfertilizing can cause pest and disease issues. Plants that get too much fertilizer (especially nitrogen and phosphorus) can grow lush, unsustainable growth that has few of the natural defenses that leaves normally have. If you’ve ever seen aphids attacking the fresh new growth of some plants in spring, you know that fresh fleshy growth is like aphid candy.

l Excess phosphorus (the P in the N-P-K equation) can create conditions where the beneficial mycorrhizal fungi in the soil don’t partner with the plants’ roots as they normally do.

Mycorrhizae are a type of fungus that occur naturally in the soil. They form a symbiotic, you-scratch-my-back-I’ll-scratch-yours type of relationship with plants, essentially extending plants’ roots further out so plants can reach more nutrients and water. The fungi take some that good stuff, but not all, for themselves.

Excess phosphorus interrupts that relationship and makes the plants do all the work of getting nutrients through their roots by themselves.

l Some soils may be contaminated with heavy metals, which means you shouldn’t grow vegetables there. A lot of things can cause heavy metals in the soil, from using treated wood in the garden, to contaminated compost and soil mixes, and even the past misuse of the land. Better safe than sorry.

l You can also conserve resources, prevent fertilizer runoff, and save money by only using the fertilizers your plants actually need.

Have I convinced you to part with your hard-earned ten bucks? Good! Go on over to the UMass website and check into what their soil testing lab can do for you:

University of Massachusetts: Soil Testing Services Offered

University of Massachusetts: Soil Test Order Form

16 responses to “Cheap Soil Testing: How and Why To Do It”

  1. Gen,

    We do a lot of soil testing, and we use UMASS for all of our chemical assays. They are wonderful to work with, and the turn around time is efficient. A couple of other things your readers should consider when testing: Ask for the standard soil test with organic matter. It costs five dollars more, but knowing the organic content in your soil is very important. UMASS also provides buffer pH and nutrient levels in ppm for phosphorus, potassium, calcium and magnesium. All important in determining what is going on in your soil. Calcium-magnesium ratio is an important, and will tell homeowners what type of limestone to apply if soil is acidic. There is much to learn from a soil test, and UMASS is an excellent place to learn about your soil.


    • Scott, I agree. It’s a great addition to the test and only another five bucks. Thank you so much for sharing those additional things to consider.

  2. That is a very cheap soil test. I’ve noticed in almost all the cultivated garden soil tests I’ve seen the phosphorous is very high. It’s a common problem: people dumping more fertilizer on because it supposedly good for plants, but it’s not even needed. I usually recommend people to go get a soil test before applying any fertilizer other than nitrogen.

  3. Gen – as usual, awesome information! I have a few clients right now who are interested in having their soil tested so the timing couldn’t be better – thanks so much! – R

    • Yay, Rebecca! More soil tests means less over-fertilizing – always a good thing.

      I’m stoked about getting some soil tests for my clients, too, now that I know such an inexpensive and reputable source.

    • Christiane, thank you so much for stopping by! It was a revelation to me, too. I was used to $60 soil tests from the Bay Area. $10 is just insane.

  4. Wow, geez. I guess I know where I’m going to get my soil tested at. Even if I had the reagents and a spectrometer, that’s pretty hard to beat!