Sunday, August 16, 2015

pH Soil Test - Homestyle

I've been fielding numerous email questions about soil, with the number one about a home test for pH. I find that home testing is simple. And because of our acidic rain here, due to the erupting volcano, plus the fact that I add soil amendments between each crop, I test soil pH frequently. How frequent? For right now, between each crop. Once I start cutting back on soil building amendments, then I'll probably slow down to 2-3 times a year. Both the volcanic acid rain and the biomass soil additives (compost, mulch, manures) contribute to acidification of the soil. 

The test I do involves test strips and/or pH paper. For the bare minimalists out there, you could use a mixture made from red cabbage that would give you a rough acid vs base result. Or for the techie oriented gardener, there are pH probes. I have a probe but I found that it needed cleaning between use for a reasonably accurate reading....and quite frankly, I never seemed to have ultra fine sandpaper on hand when I needed it. Usually I couldn't find the sandpaper because someone used it (sigh...usually me)......that is, IF I could find where I last misplaced the pH probe! I've done that plenty of times. In fact, right now I havent the foggiest idea where the dang thing is. For some reason that's beyond me, I always keep the pH testing strips & paper in my medical kit. Thus I can always find them. Yeah, I equate test strips with medical testing, thus the reason I find them in my veterinary supplies. Hey, I do what works, regardless of how silly it seems to others.

So for my home tests I need...
...pH test strips or paper. I buy them online. 
...distilled water. 
...soil sample. 

...Test strips & paper. While not the most accurate testing equipment, they are plenty accurate enough for gardening. I just need a general idea what the pH is. 

...Why distilled water? Because my catchment water comes from acidic rain. I adjust the pH of the catchment water using baking soda once a month, so on any particular day heaven only knows what the water pH actually is. By using the same gallon bottle of distilled water over a stretch of time, my test results at least are relative to each other. This gives me a better idea of the trends going on in my gardening and soil amendment efforts. 

...The sample. Getting a soil sample is simple as long as I follow a few rules. Clear off the top couple inches of soil which is primarily mulch. This upper section is not where the plants roots are. I'm targeting the plant root zone. Once I'm down to the root area, I'll simply take a scoopful and put it into a clean cup or jar. 

Next I'll add water, enough to cover the soil with the intent of having a layer of water atop the soil once the soil particles settle out. I don't have a centrifuge, so I need to either rely upon gravity to settle the soil particles or drip the soil slurry through a coffee filter.  I've often toyed with the idea of making a bicycle tire centrifuge, but haven't gotten around to it yet. If I actually had a bicycle, it would be simple, but alas I don't have one.  Maybe I could just put the soil/water mixture jar in a sling and swing it around my head for a bit. But I haven't tried that yet either. So I use the lazy gravity method by letting it drip through a piece of napkin, paper towel, coffee filter, or scrap of cloth in order to clarify the water. The only reason I want the water to clear is so that the soil particles don't interfere with my being able to see the color on the test strip/paper. Without filtering or settling out the silt in some fashion, the muddiness interferes with the color on the test strip/paper. 
(I normally don't use a coffee filter, because I'm a scrooge and filters cost money.)

Once I see some reasonably clear water, I'll dip my test strip into it and read the results. I could use an eyedropper, pipette, or even a spoon the collect that water and use it to wet the test strip/ paper. Just alternative options, but I usually just make a quick dip. 

Reading the test strip or paper is simple because they come with a color chart. Just match up the colors then read the chart. Bingo. 

I used to use a swimming pool test kit, but I found a problem..........
....As the above test shows, my soils' pH is often BELOW the test strips capability. On the above strip, the pH is the second colored square down. This test produced a barely yellowish result because the pH is actually below 6.4. How much below I couldn't tell. Thus this test kit won't do for my soils. 

Since I didn't know how much lower the pH was, I decided to use a more broad range pH test that I had on hand. I needed to know if this soil was still in the 6 range, or if it had slipped into the 5's or worse. So here's the next result......

The chart indicated that the pH is 6-ish. The color was strong enough to tell me that it wasn't slipping down in the 5 range. 

But for my routine testing, I don't use either of the above kits. While these two each have their place, I strongly prefer using these.......


The strips and paper seem to give me consistent results and are within the range most useful to me. So I took a strip and tested my sample. In the photo below, it's the strip on the left. The results indicate this soil sample is at 6.1. ......... It was the clear amber but a trace of color change was taking place but not strongly enough to darken the entire color patch to make it 6.2. But as I've said, I don't need a real accurate result, so to say the soil is 6.0 to 6.2 range is accurate enough. 

The strip on the right is another soil sample from a different garden bed. You can see that there was a stronger color change. This bed has been consistently testing at 6.4-ish. 

For garden beds that I have been using for a while, I tend to use the pH paper. I find that it's quick and simple to use, plus it's cheap. I can get a lot of tests out of a roll. The down side is that the roll can get ruined easily if I'm not careful. Dropping it into a puddle is not advisable. And forgetting to put it back into my pocket, thus leaving it outside to be rained on is also not a good idea. 
(Above-  I tear off a short strip of paper off the roll, about 1 1/2 to 2 inches.) 

The above test indicates a pH around the 6.0 and 6.2 range. **** Important----- notice that I hold the paper so that gravity lets it hang down vertically. Once the paper gets wet it is very limp. With people who are having problems using pH paper, it is often because they try to hold the paper upright or horizontal, rather than letting it hang. 

Once I know the current pH status, I can guess-imate how much coral sand, crushed bone, and wood ash to till in. It's only a guess, a gut feeling acquired from months/years of doing this. The soil that tested around 6.0 will get a heavier sprinkling of wood ash than the one that tested at 6.4. Both will get a dusting of coral sand and a moderate addition of bone. That's along with two inches of compost and a light layer of rabbit manure. 

1 comment:

  1. I get a feed from Star Advertiser in Honolulu. Said you guys were getting some rain. Did it pan out for you and that side of the island? Having a hard time imagining rain. We haven't had any for so long.

    I used the pool test strips which said my soil was as alkaline as it could be. The color on the test strip was so ferocious it was sort of like it was saying I'm STRONG so you need to pay attention! I add a phosphorous mixture which says it cures blossom end rot in tomatoes. And it does. BER comes from the plants not being able to absorb the calcium in the soil. The calcium binds to the salts I guess and not to the plants.

    I thought this was a good post because it shows how easy soil testing really is and that one does not have to go out and spend a lot of money to do it. Thanks!

    Glad to have you back!