Friday, July 15, 2011

Testing the Soil

As I have mentioned here before, I currently garden in containers. One of the challenges of container gardening is that the reservoir of available nutrients is much smaller than it is in the ground. If you have mycorrhizal fungus in your in-ground garden, it will search out far and wide for available nutrients to gather for your plants. In a container, the plants and mycorrhizae alike are limited to what is in the container’s soil.

When I made the soil, I used good quality compost. As the plants were growing, I added good fertilizer. I specifically looked for fertilizer that had rock phosphate and greensand. Both are hard to find, but both are rock-based sources of potassium and phosphorus. They should have good lasting power in the soil. There is no such thing as a rock-based source of nitrogen, though, so I had to look for other solutions. Last summer, when I was fertilizing the soil, I made extra care to add blood meal in addition to the general purpose fertilizer. Blood meal is a great source of nitrogen, even though it doesn’t necessarily have much lasting power in the soil.

Last fall I began noticing a little slower growth in my plants. This spring, it almost slowed to a crawl. My seedlings were slow to sprout, slow to come up, and glacial in their growth. All but the peas, that is. Peas, along with the bacteria they culture on their roots, have the ability to fix atmospheric nitrogen on their own. It seemed a sure sign that my soil was lacking something, probably nitrogen. It was time to break out the soil test kit.

I got a Rapitest kit that tests for pH, nitrogen, phosphorus, and potassium. Testing each pot for all 4 numbers took a while, but it was well worth it for the information gained. For those of you who haven’t used chemical soil tests, the use is pretty easy, and not too time consuming. You dig down about 3-4 inches in your soil and get about a cup of soil, sometimes mixing from a couple of different places if you are testing a larger area. Then you mix the soil with distilled water (I used filtered, which might have thrown off my results a little, but not much.) per the package directions and shake really, really well. Then you let the soil settle out, which usually takes 10-30 minutes unless you have clay soil, which might take a couple of hours. Then you dump the powder for the test you are about to perform into the provided vial and fill to the line with your test water. Shake for a few seconds and then let it sit for about 30 seconds. Then you just compare to the colors on the vial to see how much of each nutrient you have.

As expected, every single one of my containers tested as depleted or nearly depleted in nitrogen. Oddly enough, though, each one had more than adequate, even excessive, amounts of phosphorus and potassium. They also tested in the general range of neutral in pH. A couple were slightly alkaline and a couple were slightly acidic, but all were pretty close to neutral.

Now all I need to do is get some nitrogen in there so my plants can grow with wild abandon!

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