Why it’s Important to Keep Soil Healthy for Plants

Chris Fields-Johnson, technical advisor at the Davey Institute, talks about the importance of healthy soil and his Davey career. 

In this episode we cover:  

• What is healthy soil? (0:50)  
• What the soil is like where Chris is (1:26) 
• The importance of PH when planting trees (2:30) 
• Acidic soil plants (4:40) 
• Can you and should you change your PH? (5:33) 
• The importance of a soil test (7:15) 
• Luxury consumption and over fertilization (9:00) 
• How to have more organic matter in your landscape (11:10) 
• What Chris does as a technical advisor at the Davey Insitute (15:25)  
• How Chris got started in the field (18:18) 
• Should you use compost for planting trees? (21:16)  

To find your local Davey office, check out our find a local office page to search by zip code.  

To learn more about healthy soil, read our blog, How to Keep Soil Healthy For Your Plants. 

To learn more about improving soil health, read our blog, How to Improve Soil Health with Biochar. 

To learn more about soil tests, read our blog, How to Perform a Soil Test (And Why You Need One!).  

Connect with Davey Tree on social media:
Twitter: @DaveyTree
Facebook: @DaveyTree
Instagram: @daveytree
YouTube: The Davey Tree Expert Company
LinkedIn: The Davey Tree Expert Company 
 

Connect with Doug Oster at www.dougoster.com. 

 
Have topics you'd like us to cover on the podcast? Email us at podcasts@davey.com. We want to hear from you!    

Transcript

Doug Oster: Welcome to the Davey Tree Expert Company's podcast Talking Trees. I'm your host, Doug Oster. Each week our expert arborist share advice on seasonal tree care, how to make your trees thrive, arborist favorite trees, and much, much more. Tune in every Thursday to learn more because here at The Talking Trees podcast, we know trees are the answer. This week I'm joined by Dr. Chris Fields-Johnson. He's a technical advisor for the Davey Institute down in Charlottesville, Virginia. Today we're talking all about the importance of keeping your soil healthy for your plants. Hi, Chris. How are you?

Dr. Chris Fields-Johnson: Good morning, Doug. Doing well.

Doug: Well, we both love something. It's called soil.

Chris: That's right. My favorite thing.

Doug: Let's talk a little bit about our trees and how they relate to soil, and then we'll talk a little bit about planting and finding the right spot. Healthy soil, what are we talking about there?

Chris: There's lots of aspects to it. I think the key things to understand is that in most environments, a healthy soil is going to be rich and organic matter and be really well structured, have a nice aggregate structure to it, lots of porosity, lots of room for water and air movement. Roots should be free to grow in three dimensions. If you have all those things in place, the microbes are going to be happy, plants are going to be happy and you should have a site that does really well.

Doug: In general, what is the soil like in your area in that part of Virginia?

Chris: I'm in the southeastern part of the United States. Our soils here have really never been influenced by glaciation. That's one thing to understand. A lot of the minerals have been weathering in place for literally tens or hundreds of millions of years. I'm in the Piedmont region, which is an erosional environment. Here that is even more so exacerbated. Out on the coastal plain, they have coastal sediments and delta sediments and things like that, so it's a little bit fresher material.

Here in the Piedmont, this landscape's literally been eroding away in place for millions of years. It tends to be more acidic, lower natural levels of fertility, but the soil is deep, tends to have a fairly good structure because it's been forming in place and layers for so long. What it lacks in basic fertility and having lower pH and all that, it makes up for in being good structurally. It has good depth, good aggregation, water holding properties. Things like that tend to be good.

Doug: Let's get into pH a little bit. Tell me about the importance of pH when I'm thinking about planting something in a certain area.

Chris: pH is critical. It really is the master variable of all soil chemistry. The reason for that is that at different levels of pH, elements will take on different mineral forms. They'll recombine into one form or another, then maybe it's more or less soluble in water. At a certain pH, a chemical can form out of elements that is not soluble in water. If that's true, then it's really difficult for plants and microbes to access that nutrient. At a lower pH, that combination of elements might form a mineral or a molecule that's very much soluble and accessible by plants and microbes, and they can get at it.

pH has a big effect on what's available. If you have a really high pH, certain things are going to be in short supply. Iron and manganese get in short supply at high pH. At a really low pH, things like nitrogen might be in low supply. We want a balance in most cases or have a plant that's specifically adapted to some extreme. You need one or the other.

Doug: Let me see if I have this right. Regardless of how nutrient-rich my soil is, if my pH is off, my plant might not be able to use those nutrients. Is that accurate?

Chris: That's exactly right. At an extreme pH, the nutrients will be locked up. In an immobile form, plants will not have access to those nutrients. Similar concept is with soil structure. If your soil is just one solid brick, it doesn't matter if it's pH balanced and has perfect nutritional profile, if the roots physically cannot get in there to harvest that material, then it's useless to the plant. Similar concept just from a chemistry standpoint as opposed to a physical standpoint.

Doug: In the case of pH where we have too much acid or not enough acidity, we can use a certain plant to be-- I guess I'm just thinking acid-loving plants. I'm thinking rhododendrons, azaleas, hollies, Japanese Pieris. If I had acidic soil, depending on how acidic, I guess, those plants would be good for that. Is that right?

Chris: Yes, that's right. All those heather type species do great in acidic soil. They actually prefer it. They'll start having problems if you get above the mid-sixes in pHs. They'll start having issues. They like the acid soil. A lot of the hardwood forest and coniferous forests particularly in the east and the southeast, it is very well adapted to acidic soil. It'll thrive at a pH of five to five and a half, and not have any issues. As you get below five, yes, you start having problems, but a lot of our native forests, particularly in the east, really prefer an acid soil.

Doug: When I'm thinking about planting or where my trees are already growing, and I don't have the pH I want or need, can I change it? Should I change it?

Chris: You can try. It depends on how extreme the differences between where you're at and what you need. If it's a reasonable jump, then you can apply lime to raise pH or you can apply sulfur to lower pH. You can apply lots of organic material, organic mulches, wood mulches, and over time that will tend to depress pH if you're a little bit high, but it's complex. You want to do some soil testing, figure out where your pH is to begin, get a sense of the exchangeable acidity in your soil. That's that buffer capacity, the ability of the soil to resist a change in pH.

If you know those two things and the soil texture, a little bit about the mineralogy, then you can get a good prescription from a soil lab for how much lime or sulfur or whatever to put down to get you to where you need to be. You might not be able to do it in one step. You might have to put a little down every year for a number of years to get where you want to be. If you're fighting geology and climate, where having that extreme pH that's unfavorable to whatever you're trying to grow is the case because of geology and because of climate, you're going to be fighting that really indefinitely. You have to make a decision about whether that's worth it. Maybe it is, maybe it's not. Maybe you're better off just planting something that will do well there naturally and not fighting the pH forever.

Doug: Of course, it's important to get a soil test. I see many homeowners, not so much with their trees, but maybe with their lawns, just indiscriminately throwing lime on there without knowing a scientific number. If you could talk a little bit about the importance of that soil test and giving you that scientific number.

Chris: In some regions, you can make some educated conjectures about what soil is likely to contain or what its properties might be as far as pH and trends like that, but if you don't get a random sample from your lawn or your beds, wherever your area of interest is, and submit that for rigorous laboratory testing, you don't really know and you can't be precise about what you're doing. You might be throwing things off, making them worse than they were. It is important to periodically do soil testing. It's not difficult, it's not expensive, and then you can be very precise about what you do and more efficient.

If you're putting down material unnecessarily, it might not be doing harm. It might just be you're wasting your resources and your time, but in some cases, it can do harm. If you get pH way too far off or put down way too much nitrogen or some other element, you might be harming your plant material, making it more susceptible to certain diseases and pests. You could certainly be harming the environment. If you have fertilizer runoff, for instance, is a major pollutant in a lot of our waterways, causing eutrophication and fish kills and dead zones, and stuff like that. It can actually cause harm if it's way overdone. At a minimum, it's just a waste of resources and time.

Doug: Well, good. Let's talk a little bit about that. That's a great point about overfertilization or overuse of different amendments. The plant can only take up so much, and then what's left does go into our storm sewers, and we don't want that.

Chris: The plants can do something called a luxury consumption where they'll take in a little bit more nutrition than they really need. That can cause harm in a few different ways. One, you can get way too much vegetative growth. If your goal is to have flowers or fruits or some other product or aesthetic quality, then all that extra vegetative growth and leaves and longer shoots and all that might not really mean anything to you and it might be taking away from the flowers and the fruits and whatever your goal really was. The other issue there is that when you have lots of vegetative growth, lots of volume of plant material, the concentration of phyto compounds inside that plant material goes down. Those are all the defense compounds that help plants to defend themselves against pests and diseases. Some of that resilience goes away.

Then if you have a lot of extra free nitrogen, in particular, in plant sap, you're sucking and leaf-chewing insects, they consume all that nitrogen. They use that to synthesize proteins, and guess what they do with those proteins? They make babies. You can get big bumps and pest populations by having too much nitrogen applied. That is also true for certain types of leaf blights and diseases. By having too much nitrogen in the system, you can exacerbate those. Then you have an ongoing plant healthcare issue.

Yes, there is harm that can be done. Then there's all the follow-on effects of whatever the plants don't actually take up, if it's just going to leach through the soil or run off the surface of the soil, that's going to end up in the water and create a big problem there. It's going to cause algae blooms. The algae goes through a cycle, it dies, eats up all the oxygen in the water, you get fish kills and dead zones. It's a nightmare. It's better to be precise and only use fertilizer when we need it, and in the amounts that are appropriate.

Oster: In nature, in a deciduous forest, the trees leaf out at the end of the season, they drop those all there, and this goes on year after year after year. That's improving that soil there. What are we doing in our landscape to make our soil better, have more organic matter in there?

Chris: Yes. In nature, all the leaf turnover and root turnover happens on its own, and the system builds up carbon and biomass over time and accumulates nutrients, and recycles nutrients. A big issue in the green industry is that a lot of that leaf material is raked away and blown off every autumn, and it never comes back to that site. It may be composted and end up somewhere else. Some of it might be burned or landfilled, but most of it doesn't come back to where it came from. I think the best thing we could do is try to get that cycle reestablished wherever we can.

If you can create beds around trees and shrubs, and allow the leaves to fall in the autumn. Then once leaf fall is complete, there's mulch over top of them. Arrange the leaf litter in an attractive way and then mulch over top of it with an inch of wood chip mulch or a cured mulch product to make it look good, and keep those leaves from blowing around properties all winter. Then we've reestablished that natural nutrient and carbon cycle. Everything looks good, it's aesthetic and uniform. Some people, they just want natural forest litter around the trees, "Hey, that's great," then you can just leave it alone and let things cycle.

That's number one thing I think we could improve on is, let's get that cycle reestablished. In cases where that's impossible, a lot of people like the turf going right up to the bases of their trees and they're not really interested in having mulch beds, or for whatever reason, they don't want to let the leaves fall and just mulch over top of them. We do have systems where we can replace that nutrient and carbon load. We can top-dress composts over turf, and it'll pretty quickly filter into the turf and disappear. It'll nourish the turf and the trees and shrubs growing in the turf.

Then of course, we also have synthetic fertilizers, which will replace the nitrogen, phosphorus, potassium, other micronutrients. We can use that as a replacement for the leaf litter. A typical forest floor, hardwood forest, it'll release something on the order of 30 pounds-plus of nitrogen per acre per year. If we take that away, we take that cycle away, we can replace that with synthetic fertilizer, ideally, something that's slow release, that will decompose over the course of a year or so, and never really spike the nitrogen out of control.

Oster: Chris, there was some good news in there for me. Since I live in this oak forest, the way I interpreted what you just said is, I'm no longer raking those leaves. I can leave them down, I leave them in my beds. It's good for the butterflies, and certainly good as it breaks down to feed all those plants. Is that what you just told me? I hope it is.

Chris: I'm giving you permission to let those leaves fall and never touch them again.

Oster: Chris, you're my hero. [chuckles]

Chris: One less thing you have to do every year.

Oster: Oh, definitely.

Chris: Yes. I've seen lots of properties where be like an oak forest and they're in the habit of raking and blowing out all the leaves. Eventually, the soil becomes really hard and crusty, and often it'll just get colonized by moss and just loses nutritional content and carbon over time. You start to see those oaks decline in a lot of cases. They just start running out of nutrients. Yes, I'm giving you permission, let the leaves fall and walk away. One exception would be, you do want defensible space around your home and other buildings from wildfire and things like that, so you make sure you're leaving like a 50-foot buffer.

It could be xeriscape, gravel and hardscape, or it could be just green growing turf. Make sure you're leaving a buffer around your home and buildings and things like that, but outside of that, yes, just let the litter fall and cycle naturally.

Oster: Tell me a little bit about your job. What do you do as a technical advisor?

Chris: Lots of things. Primarily, I'm a scientist, so, I'm here to provide scientific support for various branches of the Davey Tree company. A lot of it is remote diagnostic and prescription support. If people identify an issue in the field, they're not sure what the cause is, you can't identify the pathogen of the past, they can talk me through it or send a photo, or we can get on FaceTime or some other platform and take a look at it. I'll help them diagnose the issue.

Then because I work as a team with a bunch of other technical advisors, and our diagnostic laboratory staff back in Kent, if I don't know the answer, I can reach out to our team, and almost always, well, one of them or another of our team members will know what the answer is. Then we can come back with a plan, work on a plan with that Davey staff member for what to do. There might be a product to apply or a certain strategy to employ to manage that problem. That's a lot of it, is that remote diagnostics support. Then another big part is training.

Whether it's teaching at our flagship programs like the Davey Institute of Tree Sciences or various plant health care updates, but also field training. I'll go around, I'll try to visit all the offices in my territory at least once per year, spend a day riding along with plant health care technicians, or arborist representatives, and looking at different issues and just doing field training. A lot of times I'll be put with more junior members of the team, and we want to work on their diagnostic abilities and help me think about our client properties.

We do environmental and safety training as well on pesticide usage, and personal protective equipment for applying pesticides. Making sure everybody has the equipment that they need, maintaining it well, handling pesticides safely in a way that's legal. I do a lot of speaking at conferences. I very frequently get invitations to talk on topics like soils and tree conservation for construction, and topics like that. I travel year round to various conferences, and that's more about just educating our field, educating our industry, and the public, and bringing everybody up to a higher level of understanding. Then I always have ongoing research projects, testing different soil care products and techniques for clarifying water with wetland techniques and things like that.

Oster: Tell me a little bit about your path to this job. Was science always your thing?

Chris: Yes. I always wanted to get into sciences growing up one way or another. I think the first step I took onto this path would have been my first year in college, I volunteered at the university Arboretum, and helping to pull weeds and pot trees and get ready for their plant sale every year. Stuff like that, and just fell in love with the arboretum there and that kind of work. I ultimately ended up transferring into forestry because of that experience. I'd really gotten into the idea of caring for the forest on my own from that arboretum experience and I was working in the woodlots and things that my family had back in Richmond.

Eventually, I transferred into forestry at Virginia Tech, and then just ran with it from there. I wanted to go more into traditional forestry at first, but there were a lot more opportunities in arboriculture in urban forestry. I ended up getting a job as a plant health care technician working for an arboricultural firm. I was out running a plant healthcare rig, providing treatments, spraying and doing injections and soil work and air spadework, that kind of thing. I did that for a few years. Then the job that Davey became available to become a technical adviser right around the time I was finishing my dissertation, and my doctorate at Virginia Tech.

Yes, it all worked out, series of random events and all that to bring me here, but I was always driven to go into science, particularly into forest tree and natural resources. The soils classes that I took as a forestry student, I liked those so much I decided to do graduate school and soils. Then my projects in graduate school had a lot to do with forestry as well. Even though I was a soil science student, I worked in a land reclamation with Appalachian surface coal mines, and getting them reforested with native forest types and American chestnuts and that kind of thing.

That was a good combination of soil and in forestry work. Then for my doctorate, I worked on biochar projects, with mine land reclamation, reforestation, and then trying to quantify the amount of charcoal left behind from forest fires to improve weather windows for controlled burning, so that we get more carbon residue after controlled burning. Yes, that got me here.

Doug: Well, the next time that we talk, I need to pick your brain about biochar, so I'm going to put that on the calendar. Before I let you go though, when we're talking about soil, in doing this podcast and talking to so many arborists about planting, we're not adding compost. If I was to plant vegetables, I would put compost in the planting hole. For trees, for the most part, we want that native soil in there. What do you do with that when you come to a point where you got the right place for the tree, but the wrong soil?

Chris: It really depends. If your soil already has adequate levels of organic matter, and for me, that means around 5% organic matter by mass or more, then adding a bunch of extra compost or biochar or whatever to the hole isn't going to improve the situation, so it would really be redundant and unnecessary. If you're starting from the subsoil material that is lacking in organic matter and has really poor structure, that soil will absolutely benefit from additions of organic material at the time of planting. A combination of biochar and compost is what I would recommend the compost is going to be more of what we call labile, more decomposable, it's going to release carbon and nutrients as it breaks down feeding microbes.

The biochar is going to be stable. It's going to help provide stable porosity and structure so that that new tree will be able to grow roots in every direction through the soil taking advantage of that porosity, air will be able to get to the roots because of the porosity and water will be able to move downwards through the soil. It really depends. It really depends on where you're starting at, whether you should amend with organic material or not. One mistake you do want to avoid is if you have a really poor soil, let's say, traditional method might be to just auger out a planting hold with a skid steer, and then plop a ball and burlap or a container plant in that augured out hole.

If you make just what's in that auger downhole perfect with biochar, and compost and just make it ideal, but then there's this sharp wall of compacted soil that's really poor just outside that planting hole, the trees not going to want to leave that hole, it might as well be in a bathtub or planter or a pot. You want to have a transition, you need to continue the treatment outward from the root ball to encourage those roots to grow outwards. It might require more site prep and thought than some landscape tree installers are used to employing. You do want to avoid that. You need the tree to survive initially, but you also want to encourage it to grow through the system outwards and not make it so comfortable in that hole and so harsh outside the hole that it never wants to move anywhere it's out there.

Doug: Well, that all makes sense to me, Chris, and I just want to thank you for all that great information. I could talk all day with you about all these different things with the soil and such but like I said, next time I want a primer biochar. You're going to have to teach me all about biochar. I need to learn about this because I keep hearing about it, so thank you very much for your time and great information.

Chris: Yes, thanks, Doug. Yes, I'd love to speak with you on biochar for a whole segment sometime. That'd be great.

Doug: That's the next one. Thanks again.

Chris: Great, thanks a lot for having me.

Doug: Tune in every Thursday to the Talking Trees podcast from the Davey Tree Expert Company. I am your host, Doug Oster. Do me a favor, subscribe to the podcast so you'll never miss one of our fun episodes. If you have some ideas for the show or some feedback, I'd love to hear from you. Send me an email @podcasts, that's plural @davey.com. That's P-O-D-C-A-S-T-S D-A-V-E-Y.COM. As always, we like to remind you on the Talking Trees Podcast, trees are the answer.

[00:25:26] [END OF AUDIO]