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!

Friday, July 8, 2011

Thursday, July 7, 2011


I have grown many mushroom logs over the years and, like any good composter, hate to throw them away when they are spent. It is still a good source of carbon and minerals and not to be wasted. I usually chop them up roughly and throw them in the compost bin, where they tumble for some time, very slowly getting smaller. When I redo one of the containers in my garden, I find I am often short on soil (due in large part to my dislike of store-bought potting soil), so I throw a chunk or two of the decomposing log into the bottom of the pot to fill space. I figure the log will slowly decompose over several years time. During that time, it will feed the soil and provide a reservoir of nutrients.

Recently, I came upon a method of soil-building called hugelkultur. The basic premise is that decaying wood harbors a great diversity of life. If you see a fallen log in the forest, it is covered with different organisms. The older the wood, the more life there is. So, according to hugelkultur, when building soil, you bury wood in the soil. The wood provides both shelter and food source for a wide variety of life. Over the course of several years, the wood will break down into a rich soil that is full of organic matter and many nutrients.

When a mushroom log is good and spent, the interior is spongy and soft. They are easily chopped up into smaller chunks with a large knife. When putting together a new pot full of soil, I like to put a layer of well-draining material on the bottom, like sand or rocks, and then a layer of roughly chopped spent mushroom logs on top of that. I mix it in well with some good compost and then make sure I have three to six inches of dirt on top of the wood. This gives new plants plenty of room to spread their roots without running into wood immediately. While a plant can push its roots through mostly rotted wood, it may have difficulty with some of the harder portions or if you use fresher wood.

Thus far, I have only found two difficulties with hugelkultur. The first is that rotting wood is low in nitrogen. This means that your soil will most likely be low in nitrogen, too, so other sources, such as blood meal, compost, and nitrogen-fixing plants are a good idea as your soil matures, especially if you are going to be growing plants that need lots of nitrogen, like fruits and vegetables.

The second problem is that wood is high in carbon, which mostly gets converted to carbon dioxide as it decomposes. This is good for your plants, providing a slow, steady supply right where they need it. However, that carbon all takes up space. This means that the level of your soil will slowly drop as time passes, sometimes by several inches. This is great for annual plants, as it gives you lots of room to add compost. However, it can be bad for perennials as they slowly get buried in the compost you have to add.

Overall, though, I really like it as a method for bulking up soil in a new bed or container. I especially recommend it for mushroom growers, like me, who have lots of spent logs laying around that they don’t want to throw away.