Soil testing

I have two square foot boxes and one box with potting mix/soil.  All were used last year, and before, and all had compost added last fall.  I tested the soils with a testing kit I’ve had 2-3 years and with which I have gotten results in the past.  This time everything (N P K) came out depleted/ deficient.  Is it my mix or the testing kit?

cathyacz wrote:I have two square foot boxes and one box with potting mix/soil.  All were used last year, and before, and all had compost added last fall.  I tested the soils with a testing kit I’ve had 2-3 years and with which I have gotten results in the past.  This time everything (N P K) came out depleted/ deficient.  Is it my mix or the testing kit?

Which kit did you get? Some of the kits come with little capsules of chemicals that you mix together. Unfortunately, those kind of kits are constantly reacting with the air, and are only reliable for a year or so.

It was the Luster Leaf Rapidtest kit.  There is a capsule for each test.  They were stored in the plastic bags in which they came.  There was no expiration date.  Still.....

cathyacz wrote:It was the Luster Leaf Rapidtest kit.  There is a capsule for each test.  They were stored in the plastic bags in which they came.  There was no expiration date.  Still.....

Maybe if you stored it with a desiccant it would last longer. With mine, some of the tests had absorbed water from the atmosphere and actually dissolved the (dark blue) capsules. If memory serves, the pH test was probably still OK.

The lesson I learned was that the next time I bought a soil test, I'd get the kind that comes in little bottles even though it's not as convenient and initially more expensive.

The tests that you send away for seem to run around $17 for home gardens and a little less if you say you're agricultural -- for a single soil test! Not counting shipping! The home garden test is more expensive because they also test for lead. That makes sense if you're starting a brand new garden in a questionable location (like a backyard) but maybe not so much if you're setting up an SFG from safely sourced materials.

On a side note, theoretically you should be able to make your own pH tests strips from red cabbage. I wouldn't be surprised if there isn't a youtube video on that.

OhioGardener wrote: The home tests for Nitrogen, or Potassium, or Phosphorous, test for the "available" amounts, and the higher the compost or organic material in the soil, the lower the "available" amounts. The microbial life in the soil releases the nutrients and makes them available to the plants as they need them, but they are not readily available as chemical or synthetic fertilizers would be. Thus, the test results are no reliable.

OG, What you wrote is the perfect explanation of why nutrient test kits don't work with Mel's Mix. As long as the Mel's Mix was made right, and the beds are replenished with blended compost, all is well. The pH is around neutral, + or - , but will be adequate for 98% of what ever is planted. An example of an exception is blueberry plants. They should be planted in their own box or pot.

A good Mel's Mix is a precious thing, and stuff shouldn't be added unless there is a very, very obvious problem.