Feed Your Soil, Cool Season Edition

We are transitioning from the summer gardening season to cool season vegetables and flowers. However, maybe you don’t want to put in cool season crops. A word to the wise: don’t leave your fading summer garden lingering (or drooping) in the garden; doing that invites insect and disease pests to overwinter in that standing debris. In its place, there are some inexpensive and easy things you can do that will not only minimize pest problems for the following year, but also feed your soil and make it even better for next year.

In today’s newsletter podcast, soils expert Steve Zien explores how cultivating an environment that nurtures soil biology lays the groundwork for vibrant plants.

Among the topics in the podcast:

0:05 Goodbye, tomatoes, squash and peppers

0:53 Feeding the Living Soil

3:56 What’s Missing from the Soil?

4:58 Understanding N-P-K

6:52 The Importance of pH

8:33 Adjusting Soil pH

9:25 Benefits of Mulching

10:23 Managing Soil Moisture

14:01 Fall Planting and Soil Care

Tips for a Healthier Soil

The University of Minnesota Extension has six tips for a healthier soil:

• Get a soil test done to find out what nutrients your garden soil is missing. Some universities offer low-cost soil tests, including U. Mass/Amherst, Colorado State, Texas A&M, and Utah State.

• Mix in organic matter. This could include fallen leaves, roots, and general plant litter.

• Incorporate compost and worm castings to compacted soil to increase air, water holding capacity, and nutrients for plants.

• Protect topsoil with mulch, leaves, or cover crops.

• Don’t use chemicals unless there’s no alternative.

• If possible, rotate crops.

Soil pedologist Steve Zien concurs, saying if people want inexpensive, easy ways to improve their soil during the winter, and they don’t want to grow cool season cover crops, two easy tasks can greatly improve your soiI: cut off your summer crops at the soil level, but leave the root system in place. Then, cover that soil with several inches (six to ten inches) of mowed-over or chopped-up leaves that are beginning to fall from the trees.

“Doing that is absolutely wonderful for your garden soil,” says Zien, who is based in Sacramento County. “It regulates the soil temperature, keeping it warmer. The fact that the leaves are ground up makes it easier for the worms that are in your soil to come up and feed, aerating your soil and taking that organic matter down into the soil. So, you will get nutrients moving down into the soil, increasing the nutrient value, and you will get more soil biology. And the more soil biology you have, the more diversity, the more numbers of beneficial microorganisms, the healthier your soil will be and the healthier your crops will be. That increase of beneficial soil biology will naturally combat pest problems.”

Zien goes on to say that the root mass remaining in the garden will improve the soil, as well. “The roots will decompose quickly,” says Zien. “The biology will basically reduce them to nothing. And there will be large pore spaces where those roots were. When you irrigate, the water will go down very nicely, which is important, especially if you have a clay soil.”

This breaking down process of the roots will happen quicker if you already have healthy soil, teeming with microbes. What can gardeners do to begin that process?

“Leaving crop residue and leaf mulch on the soil surface will still be worthwhile,” explains Zien. “The mulch and the underground crop residue protect the soil from nature’s forces of wind and water, reducing erosion and the impact of raindrops on bare soil. When a raindrop hits bare soil it loosens the sand, silt and clay particles. That moves them around in a way that results in the creation of a hard crust that seals off the soil. Topping the soil with crop residue and mulch instead will conserve moisture, reduce the need for irrigation, prevent weed growth and will insulate the root zone from heat and cold, creating a more favorable environment for the development of beneficial soil biology.”

Zien warns that part of building healthy soil may require a change in some of your gardening habits.

“One must also realize that the good soil organisms are destroyed by synthetic fertilizers and pesticides, therefore their use must be eliminated or at least minimized,” says Zien.

“The sooner you adopt these practices, the faster you will create a healthy soil food web with good soil structure and an abundance of organic matter capable of producing the garden and landscape of your dreams.”

Beyond The Garden Basics with Farmer Fred is a reader-supported publication. To receive complete posts and support my work, consider becoming a paid subscriber.

Here’s the complete transcript of the conversation with soil pedologist Steve Zien in today’s podcast (above):

Farmer Fred:

[0:00] Well, it’s the change of seasons, kind of, and you might be ripping out your summer vegetable garden. Goodbye, tomatoes, squash and peppers. Hello, broccoli, cauliflower, peas and whatever. But before you add your cool season vegetables to your garden, what about your soil? That would be what my guest would tell you. Steve Zien, pedologist, soil expert. We’ve talked before with Steve, and one of the most popular episodes in the Garden Basics series has been where he’s talked about feeding your soil. And Steve, as people change over to the seasons, to cool season, just like they would change into the spring season in March or April, this time of year, you got to feed the soil because taking out plants and putting in other plants, well, those new plants may be getting off to a weaker start unless you did something to the soil first.

Steve Zien:

[0:53] Yeah, exactly. And you’ve got to realize a lot of people when they’re thinking about putting things down for the soil, under the soil for feeding the plants, what we really have to realize is that the soil is alive. Teaspoon of soil contains more microscopic organisms than there are people on earth. And it’s these organisms that nurture your plants. They provide water, nutrients, and even pest management. And if you’ve got clay soil, and I suspect a few of your listeners have clay soils, these are the organisms that create soil structure that will open up that clay soil so that water and air and nutrients and roots and everything can move through and function. And they actually glue the sand, silt, and clay particles together and create a diversity of pore spaces so that you have these large pore spaces where air will exist in the soil. Without those large pore spaces, you don’t have any air and people have a lot of problems with their soil. You know, the goal of fertilizing and amending the soil is to create this healthy soil. You want to feed the living soil. We want to get away from the whole idea of feeding the plant. It’s all about creating a favorable environment for the soil biology, because that’s what takes care of your plant.

Farmer Fred:

[2:16] Now, most gardeners would think, OK, I’m taking out my summer vegetable garden. I know those plants used up a lot of nitrogen. So all I need to do is just add some nitrogen fertilizer and everything will be fine. In reality, if you did that, what would happen?

Steve Zien:

[2:31] Not much, especially depending upon what kind of fertilizer you use. But what you just talked about, actually, when I was in ag school 3,000 years ago, that’s what we were taught. But they did not realize at that point that the soil was alive and we need to feed the soil. And one of the things that you have to realize is that soil biology eat the most of is organic matter. And so you need to put in organic matter. And you do that not by tilling the soil. Killing the soil destroys the soil structure and actually ends up compacting the soil and kills the soil biology. So you just want to put these things on the soil surface. The best two things that you can put down are worm castings. Those are my favorite, especially if you’ve got clay soils because they contain a lot of different kinds of soil biology. And composting, just put it on top of the soil.

And then as you irrigate this time of year, because we still have to irrigate, and then later on in the season when we get rains, the rains and the irrigation will work that organic matter into the soil. Also, by putting that organic matter on the soil surface, worms will come up every single night and feed on that material and go back down in the morning.

And they’ll act as Mother Nature’s rototillers. And so they’re going to, you know, that organic material, the compost and the worm castings will eventually disappear because it’s going to be going into the soil, feeding the soil biology. And when you see that gone, time to add more.

Farmer Fred:

[4:12] What is missing from soil at the end of a growing season?

Steve Zien:

[4:17] Nitrogen is certainly one of them. And so you do want to add some sort of nitrogen source. Ideally, what I like to try and recommend people do is do a soil test. Ideally, you send your soil off to a lab and you get a full analysis, but that’s more expensive and more complicated than a lot of people want to do. But you can go to your local nursery and they have soil test kits that are relatively accurate, accurate enough for our purposes. And they will test the nitrogen, phosphorus, potash, and the pH. And then you will know whether you need to add more nitrogen, phosphorus, potash, or adjust the pH of your soil.

Farmer Fred:

[4:59] Let’s explain those terms before we go any further. I always thought our friend Giselle Schoniger of Kellogg Garden Products always put it best when explaining the roles of nitrogen, phosphorus, and potassium. She would say...

Steve Zien:

[5:12] Yeah, I like her little poem.

Farmer Fred:

[5:15] Oh, I don’t remember the poem, but for NPK, the three letters, it represents up, down, and all around. All right. Nitrogen gives you leafy green growth. The phosphorus improves the root structure of the plant. Yes.

Steve Zien:

[5:34] Phosphorus is also, though, important in flower and fruit development.

Farmer Fred:

[5:38] And then the K, the potassium, is basically for all around vigor and health.

Steve Zien:

[5:45] Yeah, it helps all of the various functions of the plant operate properly.

Farmer Fred:

[5:50] And pH is an interesting concept. It’s short for percent hydrogen. And it refers to the acidity or alkalinity of the soil, which I’ve tried to explain to people that for all those soil critters down there that are feeding your plant, These are the tunnels they run through to get to the plants, and the size of that tunnel for them to run through is determined by the pH of the soil.

Steve Zien:

[6:17] Right. And, you know, the pH where that funnel is widest, where the plants can get the most nutrients available, you know, that works for them, is when the pH is roughly somewhere in the vicinity of like 6.2 or 3, or maybe even 6.4, up to about 7. Which is actually 6.8.

Farmer Fred:

[6:40] Slightly acid to neutral, basically.

Steve Zien:

[6:42] Right. And the problem is with most of our soils in this area, because I’ve done lots of soil tests over the years. This area being…

Farmer Fred:

[6:50] The United States of America?

Steve Zien:

[6:52] No, in the Sacramento region, most of them. But in the Sacramento region, most of them are above 7.0. Most of them are above 7.2. And so that’s a little alkaline. And that does restrict some of the nutrients, in particular iron. And a lot of people in springtime, their leaves, especially of their acid-loving plants, turn yellow. And so they will go to the local nursery and say, you know, my gardenias or my blueberries, the leaves are turning yellow. And one of the issues is that the pH is just too high and the iron isn’t available. I mean, almost all of the soil tests that I’ve done, again, in this area, there’s plenty of iron in the soil. It’s just not available because the pH is too high. And so what I’ve been trying, I worked with an organization called Our Water, Our World, and we tried to educate the nursery folks on how to minimize the use of pesticides for their clients.

And one of the things that people were having problems with is this yellowing of the acid-loving plants due to the high pH. And a lot of times people would just recommend iron. And the nursery folks would just recommend iron. Oh, your plants are deficient in iron. You need to add iron to your soil. And the fact of the matter is there’s plenty of iron in the soil. And so what I tried to convince them to do is buy a pH. Sell them a pH test kit. Let them test the pH of their soil. And then they need to adjust the pH of their soil.

Farmer Fred:

[8:33] So what do you add to soil to bring down that pH number?

Steve Zien:

[8:38] Some of the things include soybean meal, which would add nitrogen. Fish hydrolyzate, which is similar to fish emulsion. It’s just manufactured a little different. You actually get more bang for your buck. Compost made with a lot of brown material, earthworm castings, and paper, cardboard, cellulose. You can chop that up and just put it on the soil surface. Again, you’re not mixing this stuff in the soil. You’re just putting it on top.

Farmer Fred:

[9:09] You know, what you’re describing could also be called mulch as well. So if you put a woody mulch on the surface of your soil year-round, you’re going to have a more balanced soil.

Steve Zien:

[9:23] Yes.

Farmer Fred:

[9:24] Talk about that.

Steve Zien:

[9:25] Well, I mean, a lot of times people get these wood chips. And I really like the wood chips because they have a diversity of particle size. And so the small particles break down and enter the soil very, very quickly and start nourishing the soil biology, which then starts nourishing your plant. And then the bigger pieces last a little longer and will provide the cooling effect in the summertime, the warming effect in the wintertime, and help conserve some moisture in the soil as well.

Farmer Fred:

[10:00] And in fact, if you keep a four inch layer of a natural mulch like that, and that could be the chip shredded tree parts from your local arborist as well. Right. Yeah. By keeping that mulch on the soil, you are feeding the soil year round, which may mean you don’t have to use as much fertilizer as you may be used to.

Steve Zien:

[10:22] Exactly. All right.

Farmer Fred:

[10:23] So, we’ve lowered the pH. Now, for our friends listening where soils are naturally acidic, it’s a low number, and they’re always dealing with, okay, how do we raise the pH to get it more towards neutral? How do you raise the pH?

Steve Zien:

[10:39] That’s actually much easier. One thing that you can use is wood ash. Normally, for our soils, you don’t want to add wood ash because, like I said, most of our soils, the pH is too high. But you can also, if you’re trying to raise the pH, you can use different forms of lime. Oystershell lime and ground limestone work very, very well. There’s also a material called dolomite lime. And in our area, I generally don’t recommend that because in all the soil tests that I did, most of the soils have very high to excessive amounts of magnesium. And dolomite has not only lime, but it also has magnesium. And so it’s adding more magnesium to a soil that probably has too much already. So you’re better off with the oyster shell lime. And you can get that at any nursery. You can also use compost that has a lot of green materials, aged or compost manures, grass clippings. But make sure to don’t put them down thick or they will mat up.

Farmer Fred:

[11:40] Dry them out first.

Steve Zien:

[11:42] Pardon me?

Farmer Fred:

[11:44] Pardon you? Let them dry out first.

Steve Zien:

[11:47] Yeah, that’s a good idea. I mean, because it’s the soil biology, again, that helps a lot in the raising of the pH or lowering the pH. It’s the fungi. And what you’re trying to do when you’re trying to lower the pH, you’re trying to feed the fungi because they put out acid materials when they’re doing their thing. And then the bacteria, the excretions from the bacteria will help to raise the pH. And so you’re basically, by adding these various things, trying to get either more bacteria or more fungi active in your soil. It’s all about the soil biology.

Farmer Fred:

[12:29] Let’s go back to adding ashes to the soil, which can make your soil more alkaline. A couple of words of warning about that, especially if your soil is already near neutral or is already alkaline, is if you’re going to add ash from the wood stove, you would only want to add, I believe, one pound per 100 square feet in order to bring it up gradually.

Steve Zien:

[12:56] If your pH is, I think before you add any wood ash, you need to test the pH. And you can go to your local nursery and they sell just pH test kits. They’re very inexpensive. And I would say if your pH is 6.7 or above, don’t use wood ash. It makes a great present for your gardening friends that live back east because they have acidic soil.

Farmer Fred:

[13:21] All right. But now having established that, what about ash from the barbecue?

Steve Zien:

[13:27] Depending upon what they’re using, if they’re using the briquettes, which most people do, I certainly would not use that.

Farmer Fred:

[13:33] Because there’s other stuff in there you don’t want to put in the soil.

Steve Zien:

[13:36] There’s other stuff in there, yeah. I mean, I use mesquite when I barbecue. And if my pH was such that the wood ash would be appropriate, which it is not, I would not mind using that. But because my pH is high enough, I don’t want to raise it anymore. I dispose of the wood ash.

Farmer Fred:

[13:57] Basically, don’t use charcoal briquette ash in your garden.

Steve Zien:

[14:00] Definitely not.

Farmer Fred:

[14:02] All right. Question came in right up your alley and also pertinent to what we’re talking about here. It’s email from Kathy who says, I have a question about my fall planting boxes. Is it OK for them to be resting in an unwatered state? If the beds are empty, should you still be watering them?

Steve Zien:

[14:20] You know, that kind of depends. I mean, it’s helpful to, you know, keep the soil biology alive and active. What I would do is put down a mulch or my again, my favorite worm castings or compost and then, you know, water occasionally. keep that soil somewhat moist and active. And if you’ve got like a raised bed or a box and you’ve got worms in there, those would probably die. Most of the soil biology would probably go dormant, but it would take them a little while to come back. So if it’s just going to be for a couple of weeks or maybe a month, I would probably keep it moist.

Farmer Fred:

[14:58] And of course, if you live in an area that gets summer rain, you don’t have to pay attention to what we’re saying. But if you live in an area where it never rains in the summertime or it’s so seldom that people take a holiday when it happens. Basically, it needs to get moistened and fairly thoroughly moistened, too. I don’t think a drip system in a raised bed turned on is going to thoroughly saturate the soil. I think you’d be better off setting up a sprinkler inside of it and thoroughly saturating the soil that way. And if it’s been dry for any length of time, at least a week or so before you plant your cool season crops, man, oh man, put that sprinkler on and let it water and make sure that that water has penetrated the full depth of the bed or at least eight to 12 inches.

Steve Zien:

[15:47] Yeah, I personally, I think if you’ve got your drip system set up properly, the drip system will work just fine. It’s just you’ve got to make sure to leave it on long enough so that that water, you know, penetrates throughout that entire box.

Farmer Fred:

[16:02] It depends, as you would know, on the consistency of the soil. If it’s a really loose, friable potting mix straight out of the bag that’s in your raised beds, there’s very little cross motion in that soil. And if you have drip emitters, it’s going to be a very narrow cylinder that descends into the soil. Whereas in a garden bed that’s comprised of sand, silt, and clay, that footprint of water from each emitter is going to be probably twice as wide as what it would be in a raised bed.

Steve Zien:

[16:36] Yeah, yeah. What you want to do whenever you irrigate. I mean, it’s the only way, in my opinion, to know how to irrigate. When to irrigate, how much to irrigate. which is basically how long and whether if you’re using a drip system whether you’re getting good coverage and that’s to dig into your soil and in in your garden and landscape where you’re dealing with soil i think a soil probe is probably the better tool to utilize in a raised bed they’ve got what’s called a soil sleuth, both of them are available online the soil and basically what you do is you push these things on the ground, you pull them out, and there will be soil in these tools. And you will actually be able to look at them and feel them to find out whether they are moist. And by shoving them in various places, after you’re done irrigating, you will be able to see whether you’re getting good coverage, like we were just talking about throughout that raised bed. And if not, then you’re going to want to, you know, apply it over the top, like you were saying.

Farmer Fred:

[17:40] The Soil Sleuth is an interesting contraption. It is so simple to look at. It is ingenious in its design. It looks like a red candy cane. It’s got notches along the inside of the long arm. And basically, you just plunge that candy cane into the ground, give it a quarter turn, lift it out, and there are little pockets of soil on each of those notches that you can feel.

Steve Zien:

[18:10] Yeah, it’s very, very cool, and it works really well in loose soil. If you’re putting it into clay garden soil, it’ll break it.

Farmer Fred:

[18:20] And for the folks at Soil Sleuth, if you want to send me some money, I wouldn’t mind.

Steve Zien:

[18:25] I use both. I use both the soil sleuth and the soil probe.

Farmer Fred:

[18:30] Okay, explain how the soil probe works.

Steve Zien:

[18:32] A Soil probe basically is a tube and a portion of the side of it is like an open window. And you push that into the ground, give it a little twist and pull it out. And you will see, you know, the whole thing will be, the whole column of soil will be there. and you will be able to see whether the soil is moist at various depths as far down as you pushed it in.

And so what I generally tell people is you use the soil probe to make sure before you irrigate that the soil is dry enough where it merits irrigation because one of the biggest problems people have in areas where you have to irrigate a lot in the summertime because they don’t get rain is they irrigate too frequently. And so the soil stays too wet, especially in like the Sacramento area where we get hot, sunny days. The surface of the soil, if you water in the morning, by the time you get home from work, that surface soil, if you don’t have a mulch on, will be bone dry. And people always think, oh, I need to irrigate again. But if you were to use your soil probe, you would find that you go down an eighth of an inch and that soil is probably moist, if not wet. And so it will, by putting it in the ground and pulling it out, it will indicate when the soil is dry enough for married irrigation. Then how much irrigation do you need? I tell people typically water half as long as you normally do. Wait an hour. Give gravity the chance to pull it down as far as it’s going to go. push the soil probe in the ground again, pull it out, and you will see how far down that water has penetrated. And if it’s gone down four inches and the roots of your plants are going down eight inches, you’ve got to double the amount of water. It does require a little bit of math.

Farmer Fred:

[20:23] We’ve learned a lot again from Steve Zien, pedologist, soil expert. Steve, thanks for your time.

Steve Zien:

[20:29] You’re welcome. It’s been fun.

Farmer Fred’s Ride for the Kids!

I’m fundraising on behalf of the 2025 Sac Century Challenge on Saturday, October 4 to raise money for the Sacramento Children’s Home Crisis Nursery, and I could use your support. Here’s the link.

On that date, I’ll probably be riding (it arrived!) my new (and probably last) bike, the FRED OTL (a custom Haley titanium bike, NOT an e-bike). “OTL” - in bike race parlance - stands for “Outside Time Limit”…participants who were sent home for being “dead ass last”. I never said I was fast. But I do persevere to the end.

The journey of 100 miles throughout the Sacramento area is to help out the Sacramento Children’s Home Crisis Nursery. I’ve ridden 100 miles in one day plenty of times…when I was younger.

But at 74, and with a few health setbacks in 2025, I could use some moral support, and the Sacramento Children’s Home Crisis Nursery can use your pledge money.

Because of those health setbacks, I’m having to prepare harder for this event. This will be the slowest century I’ve ever done, probably close to 10 hours on the bike. The doctors have not given their OK (yet) for me to do this, but to paraphrase Willie Nelson, “There’s more old bicyclists than there are old doctors, so I guess we should have another ride!”

The Sacramento Children’s Home Crisis Nursery is the only program of its kind in Sacramento County and directly prevents child abuse and neglect by supporting families with small children at times of crisis. The nursery allows parents to bring their children ages newborn to five for emergency hourly or overnight care during difficult times, with the goal of keeping families together and reducing the number of children entering foster care. To care for our community’s most vulnerable children, we rely on support from community members like you. By donating, you empower us to provide a safe haven for children throughout the Sacramento area, offering respite to parents during times of crisis, and building a strong support system for the future. Your support helps provide a safe place to stay local kids in need.

Again, here’s the link to make a donation to the Sacramento Children’s Home Crisis Nursery.

Say “Hi!” if you see me pedaling like crazy out there on Saturday, October 4th!

Thanks for reading Beyond The Garden Basics with Farmer Fred! And thanks for being a subscriber, I appreciate it!

Fred Hoffman is also a University of California Cooperative Extension Master Gardener in Sacramento County. And he likes to ride his bike(s). Thank you for your paid support!

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