QUICK, BEFORE THE FROST gets hold of the ground for good, do it: Take a soil test, to send off to the lab. Host Joe Lamp’l of the award-winning public television program “Growing a Greener World” says this simple practice is a foundational tactic of garden success, and shares other insights into building and maintaining healthy garden soil.
“Regardless of your current soil texture, structure or tilth,” Joe says, “you can change what you already have.” He calls the process a soil makeover.
Joe is a longtime organic gardener and advocate for environmentally conscious living. He took time out from work and his Atlanta-area garden to join me on my public radio show and podcast to talk soil—the basis of the food web of all life. The transcript of the November 24, 2014 show follows:
soil-building q&a with joe lamp’l
Q. Before we talk soil, Joe: I know you recently finished shooting another season of “Growing a Greener World.” What were some hits of your long journey?
A. One that was a big “aha” for me was one where we featured solitary bees—the mason bees. These are fascinating creatures, and I really took them for granted, or maybe didn’t even realize that they were out there like they are. They’re such a productive pollinator source, and we can all help promote their abundance, a helper to the honeybee situation that we are dealing with. They’re fascinating creatures, gentle—they don’t sting.
We’d had a really great feedback on that show. [Watch it at this link.]
We also did something in Sullivan County, New York, at the Center for Discovery. They’re a school in the public system, but cater to kids and young adults on the severe side of the autism spectrum with nature-based learning. It was amazing to see how the students respond with the opportunity to grow food, and garden—how they just thrived in that environment. [That episode can be streamed at this link.]
Q. The power of nature to get inside us and really heal. So often something that’s been lost in our modern lives.
A. Yes. And of course we got to visit you again, which is always fun—and filmed a show about birds and blooms, with you and also Cornell Lab of Ornithology.
Now I promised we’d focus on soil. Let’s start with a quick 101–what are the components of soil?
A. I think a lot of people would be surprised to realize that when you’re standing on terra firma, you’re not standing on 100 percent solid mineral. What you have beneath your feet is sand, silt and clay—some percentage of each—but you also have air and water vapor.
You only have about 45 percent of mineral content. Ideally there is some organic matter—roughly 5 percent in a best-case scenario—and then you have pore space, and that’s it.
Q. It’s all about the pore space.
A. It is, but you think, “Does that make sense?” because that’s the empty space, but that’s where all the life is, where the roots go.
Q. So we mentioned sand, silt and clay—from the largest to the smallest particles—but then what’s loam?
A. Loam is basically a rich, friable, crumbly soil—but as a percentage it’s roughly equal parts of sand, silt and clay—roughly.
Q. And the clay–what does it do?
A. Clay has the capacity to absorb moisture and utilize nutrients better, because there’s more surface area. Even though it’s the smallest particle of the three, because collectively there is more surface area to it, it holds more moisture.
For example, if you thought of a 2-by-4, there’s only so much surface area on it. But if you put it through a chipper, you’d have infinitely more surface area. It’s like that.
Q . When I lecture, Joe, I try to get people to stop thinking quick fixes like bagged fertilizer. I quote Harvard biologist E.O. Wilson about all the living things at or in the soil layer, which he calls, “the little things that run the world,” the bacterium and fungi and nematodes and mycorrhizae and arthropods and such—and how even though we don’t know exactly what all of them do, without them we’d be dead. They’re the basis of the food web, so why would we dump chemicals on them?
Can we talk a bit about the sort of habitat that the soil also represents?
A. Most of us have probably heard a number in the billions per teaspoon—like 4 to 8 billion living organisms in a spoon of soil. These guys are really busy. We’ve got a living network beneath our feet that we don’t even see, and we forget it’s there.
But like you said, if they were gone, we’d be gone. That’s what allows plants to thrive, and trees to thrive and give us the oxygen we need to breathe.
There are things we can do to promote those living organisms—and there are things we can do that hurt them and break them down and potentially kill that soil biology. I think we take that for granted.
So back to your comment about quick fixes—that if we throw a bag of fertilizer down and we’ll be fine. It’s almost like diet pills and junk food. The junk food satisfies our hunger craving for a while, and the diet pills—I’ve never taken them, but I can’t see how that would ever solve a longterm problem, or promote longterm health.
Q. It does not promote wellness.
A. And that’s what we need to focus on—promoting wellness—rather than a quick fix.
Q. The living things in the soil not only promote plant life, but they do all the decomposing of debris.
A. It’s not just about the nutrients, but also about everything else that’s happening in the soil—the decomposition going on there, and the way the soil aggregates bind together in a healthy, living soil.
So yes, we can buy synthetic fertilizers to provide primary nutrients for our plants—but that’s really all we are doing. There are 13 nutrients needed by plants from the soil, and typically bags of fertilizer only have three.
Q. The old N-P-K ratio.
A. Yes—but those don’t change the way the soil holds moisture properly, and the way it releases moisture properly—and conserves nutrients, and delivers nutrients at the proper time. It’s this whole ecosystem taking place down there in a balanced soil food web that doesn’t happen when you’re trying to fix a nutrient deficiency with that synthetic fertilizer.
A. It’s organic matter—that’s the only one, really. The others—the sand, silt and clay—are there natively.
As I said earlier, in a best-case scenario is only 5 percent, which is really low for it to be such an important component of our soil; how can that be? But it works. But when you do a soil test, oftentimes that number can be 0 to less than 1 percent. We have to get it higher.
Q. At least at 3 to preferably 5 percent organic matter. Now just to be clear: The word “organic” has all these other meanings lately, but what does it mean in this case?
A. It’s living organisms—bacteria, protozoa, fungi, and the other things you mentioned—and it’s also dead plant materials. Plus root exudates—what comes out of the roots that feeds the organisms in the soil.
Q. So living or formerly living material. What is the practice you follow to improve the organic-matter content of your garden soil?
A. I add a lot of compost—I make as much as I can, but I can’t make as much as I like, so I find a good bulk source from time to time.
I collect and grind all my leaves, and add them to my compost pile. I put them into my landscaped beds as shredded leaves, because that’s more natural organic matter that breaks down and feeds the soil.
Another thing I purchase in bulk: a mix of compost that also have minerals in it, such as granite dust. Compost is all organic matter—no minerals—but you need the minerals as well.
When I purchase a compost mix that has minerals in it such as from the granite dust, it rounds out the soil, and my plants perform better.
And when you have a healthy soil system, the roots secrete carbon dioxide that basically creates carbonic acid, and the acid helps break down the minerals in the rock dust into a form the plant roots can utilize. So having this balanced soil system really works, when you have not only the compost but the minerals, too.
Q. When do you add the compost?
A. I do it between seasons—when I am changing out my cool-season crops and warm-season crops, the beds are beautifully exposed, and it’s the perfect time to get in there and mix compost into the top 6 inches or so. Once during the growing season, I’ll try to add more compost and mix it in. So two major times a year: between my seasons, and then once in the fall and once in the spring.
Q. Do you even use “fertilizers” and so on?
A. A little bit—mostly in my lawn, and specifically Milorganite, which I must disclose is a sponsor of “Growing a Greener World,” though I used them long before that. It’s a non-burning source of Nitrogen, with some Iron. And I do have some deer around, so anything I can do to help deter the deer is a good thing.
Q. I read something you wrote that mentioned Sir Albert Howard’s Law of Return. Can you tell me about that? Is it sort of, “Waste Not, Want Not”?
A. Waste not, want not, yes. Here the thing: I like to think of soil like a bank account. You have your plants in a certain space, and they’re taking up nutrients. Eventually, whatever nutrients are there are withdrawn—and they are gone. We have to get them back, but how?
Again, we can add some synthetic, manmade nutrients, but I don’t believe those are needed. If we have a system where we are adding back compost and other natural, organic returns, we are making deposits that give us a really good return on our investment. and that’s what we have to do. We’ve always got to think about making deposits, not just about withdrawals.
With organic matter, it decomposes pretty rapidly, because all those living organisms are consuming it. We’ve got to be mindful of that, and think of ways to add it back.
A. I’m an advocate of soil tests for maybe an unconventional reason. There are two reasons to do one: First, we think of doing one to know what nutrients to add to our soil—that’s the conventional reason for doing the test.
But in a balanced soil system you should have all the nutrients you really need; you shouldn’t have to add more.
So I look at a soil test, or tell people to do one, I look at it from the standpoint of telling people what you don’t need to add. I think that through knee-jerk reaction, people throw in the N-P-K, and overdo it.
Q. Not even knowing what we started with, we go and do that.
A. And if a little is good…more is better… But these synthetic fertilizers are salt-based, and it’s like when we were kids, if we poured salt on a slug and watched it shrivel up. That’s what happens with all that salt on living matter—you’re doing harm, and breaking down all that living biology. I want people to avoid that.
Q. So you want gardeners to have an intimate knowledge of what their soil really contains.
A. Yes, so they’ll know not to add things through knee-jerk reactions.
I think the other most important reason to test is learning the pH level. Getting your soil in the proper level—6.5 to 7—will make use of those nutrients most efficiently.
Q. If the pH is in the extreme outside that range, sometimes even nutrients that are present can’t be taken up by plants—they’re unavailable.
A. That’s right. So if you want great results, focus on getting your pH in line, and adding organic matter.
Q. And now’s a good time to test—not in the breakneck pace of spring.
A. I have been to these soil labs, and I cannot believe the volume of soil tests that come in right at the peak of growing season, when by the time you get results back it’s too late to do anything about it for that year. Do it now. [The video at the top of the page shows how, step-by-step.]
how to watch ‘growing a greener world’ tv
TO FIND YOUR PBS affiliate showing “Growing a Greener World,” which Joe Lamp’l hosts and is executive producer of, start here. The best place to watch all the back episodes is on the GGWTV website, where they are all archived.
Joe’s and my segment about gardening for the birds, shot in September here at my place before the team visited Mya Thompson at Cornell Lab of Ornithology for the other segment on birds, will air December 27.
(All photos and video courtesy of Joe Lamp’l and Growing a Greener World, used with permission.)
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MY WEEKLY public-radio show, rated a “top-5 garden podcast” by “The Guardian” newspaper in the UK, began its seventh year in March 2016. In 2016, the show won three silver medals for excellence from the Garden Writers Association. It’s produced at Robin Hood Radio, the smallest NPR station in the nation. Listen locally in the Hudson Valley (NY)-Berkshires (MA)-Litchfield Hills (CT) Mondays at 8:30 AM Eastern, rerun at 8:30 Saturdays. You can subscribe to all future editions on iTunes or Stitcher (and browse my archive of podcasts here).