Two weeks ago, I brought a sample of my native soil in to my basic landscape horticulture class; as part of the curriculum, we were going to test the composition of our soils (for sand, silt, and clay), and I decided that it would be more interesting to bring in something native rather than the material in our raised beds. And it WAS interesting. I brought in a clump from where I recently dug to plant Lepichinia hastata (or Mexican Pitcher Sage); it was the size of a softball and it was basically like a rock. I had to pulverize it (and it took the flat top of a pickaxe to do that) and screen it and then shake it in a sort of soapy solution for ten minutes; then let it sit for a week. After a few minutes, the sand in the soil will settle to the bottom (I had no sand). Then the silty stuff will settle after about half an hour (I had no silt). Then after a week the clay is supposed to settle and you'll have a layer of water on top. Well, I followed the instructions to a 'T' and after a week there was no water. Just a thick, blackish, smelly sludge - entirely clay. My teacher took one look and said, "Did you know what the soil was like before you bought the place?" Um, no. Clearly. Which is why all our veg is in raised beds, and why we sheet mulched the entire square footage, and why I add organic matter constantly. And why I try to plant perennials that will tolerate the native soil. And why those rock-like clumps that I dig up get recycled into our compost bin for improvement.
Then I got it in to my head that I should test the amended soil in our raised beds for pH, Nitrogen, Phosphorus, and Potassium. Our raised beds were initially filled with a vegetable blend from American Soil, and have been amended every year with a layer of compost, sometimes made here and sometimes brought in, sometimes some horse manure, sometimes cover crops, etc. My understanding is that if you continue to add organic matter, the pH and nutrients will take care of things themselves. But the more I study about the needs of annual plants (which is what most of our vegetables are), the more I realize that they need optimal amounts of nutrients to really thrive. It's why I started adding Azomite, or rock dust, to my raised beds - to increase mineralization. The plants can't access those, but the various creatures and fungi in the soil can, and that eventually makes it's way into the soil 'mix.'
I bought a kit from Amazon - I wanted something simple to start with, instead of a real science kit (which I will probably invest in, in the future) - and this one seemed to have everything I needed, including clear instructions. Your local county extension should be able to give you a very good test, but our local office does not do soil testing and I'd have to send it away somewhere, which meant waiting several weeks for the results. And of course I wanted to figure it all out NOW.
I decided to take a sample from one bed in the North Garden; all our beds have been similarly amended, so I figured one sample would be enough to determine the health of all. This bed is currently housing some pak choi and tatsoi, but had paste tomatoes in it last summer. I dug down the recommended four inches and took a cup or two of the soil. Some I used right away for the pH test, which was a super fast procedure. Here is that result:
To me, that looks like a perfectly neutral pH, which was a surprise to me. I expected it to be slightly acidic, since I add so much organic matter (which tends to keep the soil slightly acidic). Most veg do prefer soil on the acidic side. (NOT spinach!) So that led me down a rabbit hole of asking some experts what they recommend - should I add a little sulfur to the beds to acidify? I consulted my LH teacher, a British market gardener whom I admire, and a friend who is a Master Gardener. None of them thought the neutral pH of my soil was anything to worry about. Plus, I'm going to be adding more compost any week now, which should take care of it, anyway. So that was good news.
Next, I tested the NPK of the same soil, which was an overnight procedure. First you make a soil solution, just like we did in class (except no soap), and right away I started to see separation of sand and silt, but zero clay! Interesting. After I let the soil settle for 24 hours, I did the NPK test. Here are the results:
Again, surprising to me. Our beds are extremely deficient in nitrogen, so I'm going to have to do something about that right away. And we have too much phosphorus and potassium. The potassium is probably a result of our watering situation - since our beds dry out so very quickly in our hot, dry weather, they go through a sort of arid phase, which brings salts to the surface. This could be one explanation of our blossom end rot every year in the tomatoes. So I need to figure out a better way to mulch the raised beds. Clearly the straw I put around the tomatoes is not doing the trick - it's just not thick enough, or not dense enough, I'm not sure. So I'm working on finding an alternative. A low-growing cover crop would solve both the mulch problem and the nitrogen problem, but the bad side of that is that the area beneath the tomatoes would be crowded, which isn't good for them - they like a lot of air and light. So I'll continue to think about that. Meanwhile I need to add blood meal or fish meal to the beds to correct the nitrogen problem, before I do my late spring planting.
This was an interesting project, and one I have eschewed all these years because I thought it would be too hard a process, plus I also thought my soil was perfect in the raised beds since I've basically created it from scratch. I was wrong on both counts, and I'm glad I know more about the makeup of my soil and how to correct it, so that we can have a banner crop of tomatoes this summer.
PS: I know many of you would like to know if the bees tried to swarm again yesterday. I was gone until about 1:45; when I arrived home, I went immediately to look at them, and the bees looked totally normal. I saw pollen going in the hive, so they were just going about their business as usual. The weather was unsettled, though. Today it is sunny, so if they are going to make a break for it, today's the day. But the warmer weather also means I can get into the hive this afternoon and see what's going on. So I'll report on all of that tomorrow, that is if there is anything interesting to share. Meanwhile I wanted to comment that I don't mind so much if the bees swarm. It's something bees do, and maybe we'll have an even better new queen, and we are not in it for the honey or the production, so we don't have to worry about losing some bees. What I would very much like to do is catch them if they do swarm and put them to use for someone else. So I'll be watching carefully today.