WHAT FERTILIZER should I feed my (fill-in-the-blank) plant? A lot of you ask that question, about things ranging from magnolias to tomatoes. Soil fertility, and how to best achieve it, is today’s topic, with long-time organic gardener and author Lee Reich who, among his three postgraduate degrees, has one in—you guessed it—soil science.

All those different fertilizer formulas in the garden center, labeled for particular kinds of plants, seem to imply that we need to add something, no matter what. But is that always the case? Lee, the author most recently of “The Ever Curious Gardener: Using a Little Natural Science for a Much Better Garden,” talked with me about building healthy soil and growing healthy plants. That’s Lee, above, with his nose in a handful of homemade compost, which we talked about, too.

Plus: You can enter to win a copy of his latest book by commenting at the very bottom of this page.

Read along as you listen to the June 24, 2019 edition of my public-radio show and podcast using the player below. You can subscribe to all future editions on iTunes or Spotify or Stitcher (and browse my archive of podcasts here).

using fertilizers, or feeding the soil? with lee reich

Margaret Roach: I knew who to call for this one, Lee.

Lee Reich: I hope you’re right.

Margaret: The soil scientist, with all the PhDs, or whatever. [Laughter.]

Lee: Just one.

Margaret: Just one of those, but a couple of master’s degrees too.

Lee: Right.

Margaret: So, we had better come clean first, before we get started on the details right off the bat: When is the last time you bought bagged fertilizer, do you think?

Lee: Uh, geez. That’s the toughest question you’re going to ask me today.

Margaret: Exactly. [Laughter.]

Lee: Not in memory.

Margaret: Exactly. And for me, I have to say, maybe every five or seven years, I look at what is laughingly called the lawn and I think, “Oh, maybe I should get some of that processed sewage sludge organic fertilizer or whatever stuff.” I feel sorry for the lawn. And literally, it’s like every five or seven years. And then I don’t do it again for at least that long. So you and I are-

Lee: I’d be afraid to do that, because then I’d have to mow the lawn more.

Margaret: So I’m asked, as I said in the introduction, I’m asked about this a lot—the “What fertilizer to I need on my fill-in-the-blank?” Are you asked that a lot too by people?

Lee: Yes. And marketing goes a long way to having them think they know what fertilizer they need.

Margaret: Right. So what’s Lee’s basic fertilizer philosophy? And you do cover this in the book, “The Ever Curious Gardener,” but tell us what’s sort of the basic idea? How do you think about fertilization?

Lee: So my basic philosophy with fertilization is very simple. And first of all, it is organic. And there’s a reason it’s organic. And I could tell you the reasons, but organic fertilization is better than non-organic fertilization. And then it becomes a question of what exactly is organic fertilization?

Margaret: And? [Laughter.] You’re going to leave us hanging?

Lee: I was waiting for the prompt. So organic fertilization means, really, the organic in organic gardening comes from organic materials, which are bulky materials, like straw, wood chips, compost, anything that was, or is, living. So the whole thing is that this is really the best way to nourish plants. And there are certain situations where you might have to do it non-organically, very specific situations. But generally organic fertilization’s best, because this is how plants have evolved to feed best, and also it’s simpler.

So my go-to fertilizer, and it can’t really be termed as a fertilizer, because you have to have a certain level of nutrients in something for it to be called a fertilizer. And my go-to fertilizer, except it’s not a fertilizer, is compost. And compost is not legally a fertilizer, because it’s not high enough in nutrients. It’s not concentrated enough in nutrients, but this is exactly what I’m looking for. Something that’s not concentrated in nutrients. Something has all this bulk material associated with it that really benefits the soil in so many other ways.

You know, it’s analogous to, people used to think, like in the ’60s, probably people came up with this idea, just take a pill, you won’t have to eat, you’ll just take a pill, and it will provide all your nutrition. And then they began to realize the benefits of fiber in the diet. So organic materials are to a plant diet, what fiber is to a human diet. It doesn’t provide a high concentration of nutrients, but it provides many of the benefits and also, at the same time, adequate nutrients. [Above, Lee’s compost bin system.]

Margaret: Right. And so, in a way, when you said a minute ago, something about like you’re following the way that plants have sort of evolved being fed, I think of the forest, right? And I think of trees dropping their leaves beneath them. And even herbaceous plants, you know, withering at frost, or whatever. And all that bulk, organic, fibrous material falling and eventually degrading into the soil. In a forest, that would be the duff layer. I think of that as like high fiber, organic, bulky fertilization, even though it’s not technically fertilization. Is that what you’re saying is the inspiration?

Lee: Yes, exactly that. There is one difference, though. So I grow a lot of fruits and vegetables.

Margaret: Yes.

Lee: Especially with vegetables, which really take up a lot of nutrients in the soil, you can’t just keep removing vegetables and not add more than just their leaves as they fall to the soil, or even digging them back in. So you have to add something extra. So that’s why I actually make compost, or people can buy compost also. There’s a lot of good places to buy compost nowadays. And I just add extra compost to the soil. Basically, that’s the only thing. I have very intensively grown vegetables, and that’s the sole way that I feed them.

Margaret: So, when people are worried. Again, the other day someone wrote to me, their magnolia, they wanted to know what to feed their magnolia at this time of year as spring turns to summer. And everyone wants to know how often to feed their tomatoes and so forth.

Lee: [Laughter.]

Margaret: But you and I aren’t doing that. We’re instead, I use that kind of expression “feed the soil,” like where we’ve been for a million years doing this protocol that’s about soil fertility and tilth and building up the organic matter in the soil.

But do we ever worry? Do you see things and think, “Oh gosh, I better do something because that plant’s not well.” Do you take a soil test? Do you know what I mean? Are there ever moments when you want to do an analysis?

Lee: Well, I do, about every 10 years, I guess I get slightly worried.

Margaret: [Laughter.]

Lee: I think maybe I’m deluding myself and I’m doing something wrong. So then I do do a soil test. And it always comes out fine.

Margaret: [Laughter.]

Lee: You see, the one thing interesting about the soil test is it turns out… You know when you fertilize organically, the main nutrient of concern, because when you fertilize organically, not only are you feeding them N, P and K, nitrogen, phosphorous, and potassium, that everybody sees on the fertilizer labels of packaged fertilizer, but you’re also feeding them, just incidentally, a whole slew of micronutrients and other macronutrients. But the only nutrient that really would be of concern with organic fertilization, would be nitrogen. And there is no good soil test for nitrogen, so I look at how the plants are growing, and that’s how I tell if they have enough nitrogen.

But the interesting thing with nitrogen… And also any of those things you mentioned like, people wondering, should I feed my tomatoes now? And then often on the fertilizer bag they’ll talk about, well feed now and then feed in a few weeks again, and then feed in a few weeks again, and you’ll keep side-dressing it.

But you know, I know people like to fiddle around, but you could put your time to better use. Because if you fertilize organically, basically the nutrients are released from the organic matter slowly, and in response to both moisture and warmth. And guess what? Plants also grow in response to moisture and warmth. So therefore, the nutrients are being released somewhat in sync with plant growth. So this is one reason that I think organic fertilization is better than fertilizing with chemicals.

Because, well, first of all, it’s released in sync with plant growth. And then all you’ve got to do is fertilize once a season. You don’t have to do it on and on. Once a year in my vegetable garden, which, as I said, are the heaviest feeders, once a year I put down compost, and that’s it. I don’t think about fertilization again.

And things that don’t take as much nutrients, like for instance, my fruit trees or my ornamentals, I just use any organic mulch I can find. It could be wood chips, it could be straw, it could be hay. Any of those things, they’re not rich in nutrients, and they don’t release nitrogen initially as fast as compost, but they are releasing it over time. And as you get a buildup in soil organic matter, over a long period of time, it’s not like you have to fertilize this month for next month’s growth, you’re adding stuff to the soil now that’s for years and years going to be nourishing your plants.

Margaret: Right. Because soil really serves a lot of different purposes. I mean, it helps plants… Well, they root into it. [Laughter.] So it helps them stand up. It does a lot of different things. I mean, the soil as a medium. And even if your soil has all the elements present, if you have a full soil analysis….  I’ve read many times about blossom-end rot on tomatoes. It’s not sometimes that elements are missing, so dosing it with a bag of whatever, it may not help.

It’s that, even if the elements are there, they can’t be taken up, because there’s some, as a non-scientist I will say, “mechanical failure.” There’s some issue. Maybe there’s been drought and then ample water, or irregular watering or whatever. There’s been some stressor, maybe, that has limited the ability to take up certain elements. I mean, isn’t there a complex … it’s more complex than, “Ooh, I don’t have enough of this or enough of that.”

Lee: Oh yes. Well, that’s one of the other beauties of organic fertilization. You don’t have to be as specific with a lot of other aspects of the soil, because the organic fertilization… And when I say organic fertilization, I don’t mean putting down a concentrated organic fertilizer.

Margaret: Right. Not a bagged material.

Lee: I used to use soybean meal, which is 7 percent nitrogen, because I thought I needed that extra nitrogen in addition to the compost. For years I made a calculation, but I was afraid to really just walk my talk on that one. But then I figured I should do that, and everything has been fine.

So bulky organic matter has a lot of physical, a lot of nutritional, and a lot of biological benefits in the soil also. So for instance you mentioned blossom-end rot. Typically blossom-end rot comes because the plant can’t take up calcium and transport it within it fast enough, often when it’s dry out, but if you add a lot of organic matter to the soil, it helps to hold moisture, which might help with blossom-end rot.

Or another example is people often… You know, if you look at charts, I always find it somewhat humorous if you look at charts for pH. You know, what the pH of the soil should be, 6.8 for this plant, 6.3 for this plant, 7.1 for another plant. And people get very exacting with this. And if you have a lot of organic matter, it buffers pH, so you don’t have to be as exact, getting the pH exactly right. Just add a lot of organic matter, and sort of everything will be O.K.

Margaret: So you said you “fertilize organically” each year. So how much you’re using compost, I think, and how much top-dressing—because you’re no-till in your vegetable areas. I know you don’t disturb the soil. In some areas, you haven’t disturbed it in 30 years. I mean, you even carefully, when you’re cleaning up in the fall, you don’t just yank everything out and upend the soil, you’re careful about how you even clean up. So how much compost do you add? How deep?

Lee: So I made a calculation once of how much, because you can sort of estimate how fast—say stable organic matter, which compost is—how fast it would mineralize nitrogen. And mineralization is the changing of organic nitrogen, which plants generally cannot take up, to a type of nitrogen that plants can take up, which is basically nitrate nitrogen and ammonium nitrogen. And it turns out that if I put down an inch, 1-inch depth of finished compost a year, that will feed my vegetables for the whole year. So I put down that every year. And as I said, my vegetables are very intensively planted, and I start early in the season, and I grow late into December. And my plants don’t suffer from any nutritional deficiencies.

Margaret: Right. And so, you make compost beautifully, and I’ll give a link so that people can read our conversation about that, and watch some of your videos about [above], I think one of your videos is something like, “You won’t believe what I compost!” [Laughter.] Or something.

Lee: And you won’t.

Margaret: And he does. He really does. Including his old blue jeans. [Laughter.] So you make a lot of compost. I make a lot of compost, but not as beautifully maybe as you do. And I do top-dress my beds, as you just were describing, similar amounts each year, and have been doing that for eons. I also, even in my ornamental beds which, as you point out, aren’t as demanding because we’re not harvesting, harvesting, harvesting, replanting, replanting, like in the veggie areas. I use composted stable bedding.

A local farmer, who used to be a dairy farmer, has turned his operation into this instead, and gathers all this material that’s been utilized in animal stalls, and composts it hot. And it’s kind of bigger than wood shavings and smaller than wood chips, but animal wastes have been deposited on it first. So it’s kind of a little manure and so forth, as well.

And, honestly, people come to Open Days, and they say, in the ornamental areas, “Oh, how do you grow that so beautifully? How do you grow that? How do you grow that?” And I’m like, “I don’t know. I’ve just been putting this stuff on the soil every year for 30 years.” And I can dig a hole, like to plant a plant, I can dig a hole with my hands, it’s so friable, or whatever the word would be. [More about Margaret’s thoughts on a good organic mulch layer.]

Lee: That is the word.

Margaret: Yes, friable, yes. So, you mentioned pH, and the buffering effect that organic matter can have, when it is present in the soil, on pH and tolerance around pH. But with extreme plants, like you grow beautiful blueberries. Do you do something different there? What are you doing these days with blueberries in an ongoing way?

Lee: Well, the blueberries as you’re alluding to, do need much more acidic soil than most plants. So initially, and periodically, I do add sulfur, which is a naturally mined mineral, which I realized is the most reliable way of lowering the pH. But I don’t really do it that often. I used to do it every year, and I haven’t done it for a few years. And basically my fertility program, which sounds more complicated than it is, for my blueberries is: I lay each fall, after the blueberry leaves fall, on top of the ground, I put down about a 4-inch depth of any weed-free organic material. Some years it’s wood chips, so it’s free. Free and weed-free. And some years it will be wood chips, some years it will be autumn leaves that people put out in their bags, and I pick them up and put them under there.

Once again, I used to do soybean meal for the nitrogen, and then some weed-free organic material. But my blueberries actually grow so much that I think they’re growing too much. So now I stopped using the soybean meal. So just wood chips. And I will periodically check the pH, but more importantly I’ll look at the leaves. Because the leaves show what’s called an interveinal chlorosis, where the veins stay dark, but the rest of the leaf is turning yellow. If I see that, that will be a definite sign that the soil needs to be more acidic.

But really, it’s not that critical, because the effect of all that organic matter, as I said, just buffers.

Margaret: Buffers, yes.

Lee: The effect of the soil pH.

Margaret: Well, and I’ll also give the link to our more thorough conversation about blueberries, but I was just curious about that. So, in the last few minutes, all this organic matter, I know you have a sign outside your … I believe, you have a sign outside your driveway that says, “Wood chips welcome.” Or something. What’s-

Lee: “Wood chips wanted.”

Margaret: Wanted. And so local arborists can dump off a load at Lee’s. Is that the idea? So you’re recruiting the stuff, yes?

Lee: Right. Usually a local landscaper dumps off a giant truckload of leaves each fall. And then arborists, when I put the sign out, eventually I do get a load of wood chips. And then at a local development where they have tons of trees, and everybody rakes up their leaves, I cruise that neighborhood. And I also have an email list from those people, which is really close by, and I’ll get truckload upon truckload of leaves to spread all over, not my vegetable garden, but I’ll put that under trees, blueberries, stuff like that.

Margaret: So as much as you can get your hands on, is what you want. Because the idea being that this is going to improve the tilth and the fertility and the moisture-holding capacity, and all kinds of good things. The microbial life, all the good living stuff inside.

Lee: Yes, microbial life is not an insignificant reason for doing this also. That’s what microbes eat, is organic matter, high-carbon material. And by giving them all this food, you really foster the growth of beneficial microorganisms.

And even most of them with the nutritional part, the nice thing about the organic matter is that, not only as it decomposes slowly, it feeds the soil, it also releases nutrients from the soil that are already locked up in the rocks—you know, small rock particles. And also adds organic—in the organic chemical sense—matrix to some nutrients in the soil, like iron, that makes it more available. So even though iron might be in the soil, it might be unavailable to plants, but when the organic matter gets around it, then plants can take it up. There’s all sorts of benefits, physical benefits—better aeration, better water retention. I feel sort of like a preacher, but it is all good.

Margaret: Well I think the two of us… And we came at it from different perspectives. You had the scientific training, I did not. I was a home gardener, self-taught, whatever. Two different spots, albeit in the same general zone. Two different spots, two different soil types that we were working with, you know. I’m on a steep hillside, whatever. It works. [Laughter.] It really works.

Lee: Exactly.

Margaret: It really works.

Lee: I think the important thing is that people keep saying simple. Generally simple works better.

Margaret: Yes.

Lee: And also, not be too swayed by ad copy.

Margaret: No, I know. I know. And to feel as if you’re, “Oh, I didn’t give it that, and so I’ve done something wrong.” Put your efforts into building the soil, yes?

Lee: Right. Right.

Margaret: Well, Lee, I’m always interested to talk to you, and I love the book, “The Ever Curious Gardener.” And it’s good to talk to you as always. Hope I see you soon.

more chats with lee reich

• The science of gardening
• How to make compost
• Fruit: pawpaws and persimmons, or blueberries or figs or raspberries & gooseberries
• Lee’s website

enter to win ‘the ever-curious gardener’

I’LL BUY A COPY of Lee Reich’s latest book, “The Ever Curious Gardener,” for one lucky reader. All you have to do to enter is answer this question in the comments box at the very bottom of the page:

What’s your approach to “feeding” plants? Do you use certain fertilizers, or compost, or both–and have you ever had a soil test?

No answer, or feeling shy? Just say something like “count me in” and I will, but of course a reply is even better. I’ll pick a random winner after entries close at midnight Tuesday, July 2, 2019. Good luck to all; US and Canada only.

prefer the podcast version of the show?

MY WEEKLY public-radio show, rated a “top-5 garden podcast” by “The Guardian” newspaper in the UK, began its 10th year in March 2019. 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. Or play the June 24, 2019 show using the player near the top of this transcript. You can subscribe to all future editions on iTunes/Apple Podcasts or Spotify or Stitcher (and browse my archive of podcasts here).