GB 324 Q&A - Nitrogen Sources. Soil for a Raised Bed.

Garden Basics with Farmer Fred

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Show Transcript

GB 324 TRANSCRIPT Q&A Nitrogen, Raised Bed Soil.


Farmer Fred  0:05

Welcome back to the Tuesday edition of the Garden Basics with Farmer Fred podcast. Unlike the Friday edition, we're dedicating the Tuesday podcast to answering your garden questions. Stay tuned to find out how you can get your garden question into the program. So come on, let's do this!




Joel  0:25

Hello, Farmer Fred. My name is Joel and I live in Fremont, California. I have a question about how to test for nitrogen in my soil. Recently, I sent several samples from my garden to a lab, which returned reports indicating low nitrogen. Thanks to you, I am aware that such reports of nitrogen are unreliable, and some other labs don't even report nitrogen. Do you recommend an ultimate way to check for nitrogen? Would simply adding compost on a regular basis be sufficient to replenish the nitrogen without testing? Thank you so much for your information. I've learned so much from you through the years.


Farmer Fred  1:01

Joel, thank you for listening to the Garden Basics podcast , I appreciate it. Debbie Flower is here, America's Favorite Retired College Horticultural professor.  Debbie, we have talked in the past about nitrogen, and the fact that it's a very important fertilizer ingredient. But it's also very elusive, too, because it wants to be a gas.


Debbie Flower  1:22

Yes, it wants to be a gas. And also if it's in the soil, it moves with water, so it can quickly move out of the root zone.


Farmer Fred  1:29

So how do we solve Joel’s issue here? I've been measuring nitrogen, and I've seen a lot of soil reports. And Joel is right, they don't even talk about nitrogen, because nitrogen is hard to measure, unless it's really an overabundance of nitrogen, then the report might mention that. But usually, nitrogen is here one day and gone the next.


Debbie Flower  1:47

Right. With students, we use tests where you wet the soil and take the water that's come off the top of the soil and mix it with chemicals to get the color. And then the color tells you how much nitrogen you have.


Farmer Fred  2:03

And those tests can be found at any nursery. They're called NPK tests. Right?


Debbie Flower  2:08

Right. I like them. And I like the ones that are a little more sophisticated. I can't think of the brand at the moment… the Lamotte soil test kits! So I use those with students. So you can do that yourself. The instructions are pretty clear, the only thing you probably need is some deionized water, something that you wouldn't necessarily have sitting around your house. And the test kit, but they're not super expensive. They're not super cheap. They tend to have multiple tests per kit, and you can replace the reagents, also called the chemicals you need to produce the color. So if you're interested in checking your own nitrogen soil content, that is one way to do it. I did a little bit of research on the type of resin tests you used. They seem to be fairly new. And everything I found was an experiment by an academic institution testing whether they work very well or not. And everybody said they do they work well, they explained how they work. And as long as the resin capsules are in contact with the soil, the correct amount of time, I don't know what the directions were on the the tests that you received. But one experiment I read about said if there, they're not long enough, they don't tell you how much is actually there, they haven't accumulated it. And if they're there too long, the resin capsules have accumulated a lot of the nutrient and then they start to give it back to the soil. So the amount they're reading will fluctuate depending on time. And so hopefully that was addressed in the directions you got on that soil test. The way I judge if I have enough nitrogen in my soil is the response of my plants, they will show nitrogen deficiency symptoms if there is not enough there. The classic nitrogen deficiency symptom is yellowing of old growth. So typically that's on the bottom of the plants. And that can occur for a number of reasons. Nitrogen being one, but also shade being another. And this is critical at the same time that those yellow leaves are falling off, you're getting new growth, so the plant is still active. But the leaves at the top that are forming are not getting as big as the other ones, you're getting small new growth. And that's because nitrogen is as it is in the air and in the water is mobile in the plant. When the plant runs out of nitrogen in the soil. It will take it out of the oldest leaves that used to be in the sun but are now in the shade and it will move it to the new growth but it's not a super efficient conversion. And so the new growth isn't as big as the old growth that is being sacrificed for it. So that is the classic nitrogen deficiency. A general yellowing of the plant is also a classic nitrogen deficiency. So those are symptoms I look for on the opposite end. And if you apply too much nitrogen, you'll get incredible rapid green growth, you may lack flowers and fruit, and you probably will have an aphid population in your newest growth because the leaves are growing so fast, the plant doesn't have enough energy to cover them with a waxy coating quickly enough to prevent the aphids from attacking them. So you can sort of if you're very observant of your garden, you can sort of adjust sort of figure out whether your plants have enough nitrogen or not.


Farmer Fred  5:28

Yeah, it's an interesting thing to it, especially about the new growth at the top because most people are looking at the tops of the plants and not the bottom of the plants, and may not notice the older yellowing lower leaves or think that's normal. But that definitely is significant, the smaller leaves at the top. And sometimes they're a little bit distorted.


Debbie Flower  5:45

It could be they just can't grow as well.


Farmer Fred  5:49

Yeah. So that is something to keep your eye on when it comes to a nitrogen deficiency. And as you mentioned, the whole purpose of nitrogen is that green growth, because with green growth, you get leaves. with leaves, you get photosynthesis. with photosynthesis, you get more plant growth, right?


Debbie Flower  6:05

More plant food. Yeah. So then the question was, can adding compost, provide sufficient nitrogen? Depends what you're growing, I would say if you're growing something and you're harvesting part of it, food primarily. Or you're cutting, it's a cutting garden for flowers, something like that where you're removing enough stuff, enough plant food stuff that you probably can't replace the nitrogen needed to continue that harvesting, growing and harvesting just with compost. If you're growing trees and shrubs for nice ambiance in the landscape, then mulch is often sufficient. So it depends what you're growing.


Farmer Fred  6:50

A combination of mulch and compost, I think is is all a garden needs for most crops. But you're right. There are some crops that are heavy feeders, like corn. Here's a plant that gets six feet tall, and uses a lot of nitrogen to get six feet tall with mostly green parts and maybe a couple of ears of corn, if you're lucky. You're better off if you are growing corn in your garden would be to rotate it through various points in your garden on a yearly basis.


Debbie Flower  7:19

Yes, there are charts you can read. And I think Fred has posted one, a pie shaped chart of rotating vegetable crops so that the heavy feeders like corn and cucumbers are maybe preceded by a nitrogen fixer like peas, and that's a way to add nitrogen. If you are growing edible things, one tactic is to grow a cover crop, it's called, or sometimes called green manure. That fixes nitrogen and that's happens underground on the roots and you cut off the tops of the plants before they flower, ideally, because a lot of the fixed nitrogen is used to produce the flower. For instance, fava beans are for us in California are a nice winter cover crop. But if we let them flower and produce beans, then we're not getting as much of the nitrogen left in the soil. The nitrogen left in the soil is on the roots of the plants and it becomes available after the plant has died. So you chop off the top of the plant, ideally before it flowers and fruits. You can compost that, or chip it up and use it as mulch, whatever you prefer, but then the nitrogen underground becomes available. And then of course there's always fertilization, and you can fertilize with organic products. Manures have different amounts of nitrogen in them. chicken manure tends to be one of what we call the hottest. Meaning it has the highest amount of nitrogen. Don't use it unless it's been composted. My mother collected some out of her father's chicken coop, a chicken coop that hadn't been used for 40 years, the chicken manure had been just sitting there, dry. And she put it on our vegetable garden and killed everything. Okay, you got to compost it, it's too hot, too much nitrogen in it, but you can buy composted chicken manure in bags that has some nitrogen value. You can buy pelleted chicken manure in bags that has good nitrogen availability. And of course  it's renewable. There are chickens that are pooping all the time. And you can buy steer manure, it's not nearly as high in nitrogen, you can buy fish emulsion, which is made from fish and is has a nice gentle amount of nitrogen and some micronutrients which are critical in plant production as well. So there are some more renewable, non synthetic sources of nitrogen that are good for the producing garden when you're cutting and removing fruit or flowers or  what have you and need that higher amount of nitrogen.


Farmer Fred  9:56

A cover crop is a great thing to put into your nitrogen replenishment gardening habit, most definitely. Like Debbie says, you got to chop those plants up, as soon as you start seeing flowers appear. because you want the energy going to the the soil root area where the nitrogen can be used, as opposed to sending it off to develop flowers and seeds. So by cutting it down in little bitty pieces before it completely flowers, at least before 50% of it flowers, you're going to be helping out your soil a lot. From what I understand, I guess you could just chop it up in little pieces and leave it on the surface, although I've heard of people doing that, but I think that would allow a lot of nitrogen to escape from the soil, right.


Debbie Flower  10:42

Do you want to bury it? Cover it with mulch? Yes, nitrogen becomes gaseous, or just dig it down into the soil with a broad fork. That might allow you to do that, because it can create openings. A broadfork is like a big garden fork. A typical garden fork is stiff with four or five tines, usually. But a broad fork can be three feet long, four feet long, however wide your bed is. And  it has many tines and you just plunge it into the soil, rock it back and forth, you get a little opening, you can throw stuff in there. And then you move over a few inches and do it again, that closes the opening you just made and makes another one where you can put in more.


Farmer Fred  11:19

A little bit goes a long way, too. My big problem was with  synthetic fertilizers. There's usually way too much nitrogen that the plant will never get to.


Debbie Flower

And it becomes pollution.


Farmer Fred

Exactly. Yeah. And there are much more slow release nitrogen fertilizers on the market these days. I know that at the Fair Oaks Horticulture Center, they like to use chicken poop based pellets. Right.


Debbie Flower  11:46

And I bought a bag of that, its called Nutri-Rich, I believe. Yes. Right. Costs a pretty penny. But it goes a long, long way.


Farmer Fred  11:54

What  is the application rate?


Debbie Flower  11:55

I can't tell you off the top of my head. I could look it up.


Farmer Fred  11:59

Well, maybe if it's there, you could.


Debbie Flower  12:01

Nutri Rich fertilizer pellets  use 500 to 800 pounds per acre.


Farmer Fred  12:07

All right, well, let’s say you have a eight feet by four feet garden.


Debbie Flower  12:12

Eight to 12 pounds per 100 square feet. Yeah, it's not a very heavy application rate.


Farmer Fred  12:19

Eight to 12 pounds per 100 square feet. Right. and you work it in. You don't just lay it on the top.


Debbie Flower  12:27

I work it in shallowly and then water I rely on water to move it down. Okay.


Farmer Fred  12:31

Yeah, fish emulsion is an old standby for a low nitrogen fertilizer that works because it slowly breaks down. A lot of people like worm castings, too, I would put that into your mix for replenishing the soil as well. And you're right, that broadfork does a great job of opening cracks in the soil to allow you to just pour the the worm castings into there.


Debbie Flower  12:56

Yeah, you don't have to go real deep. Because nitrogen moves with water, water is applied at the top and it goes down through the soil. So it will pick up the nitrogen near the surface and carry it down through the soil.


Farmer Fred  13:09

A word about mulch. A lot of people like to use bark, they call  the snad and gravel place and have 10 yards of chips delivered, for example. And all those chips are the same size. And a lot of them are big. And it takes a long time for those to break down to feed the soil. Whereas your local tree company, when they go out and chop down a tree, they're not just chopping the tree, they're chipping it and shredding it and blowing it into the back of their truck. And there's no reason that truck can't stop at your place and dump it off in your driveway. And it's all different sizes. And as the smaller parts work their way in the soil, it's feeding the soil, but the bigger parts are still on top. And they're protecting the little stuff and protecting your soil from rain as well.


Debbie Flower  13:54

Yeah, it's good stuff. I have very black rich soil. It's gotten to the point and because I apply arborist chippings regularly, not yearly, every two or three years, I'd say. But I always have a pile in my yard because I'm always doing another corner. It's gotten to the point where I can't grow some plants that like lean soil, because I have my soil spoiled.


Farmer Fred  14:19

I would like to make an argument for using shredded leaves. the leaves that fall from your trees in the fall, especially your oak leaves. And I like to run them over with a mulching mower or stick them in a metal trash can and chop them up with a string trimmer. And then just pour it on top of my raised beds, four inches six inches deep for the entire fall and winter.


Debbie Flower  14:42

And I think that's a better choice for the vegetable garden than wood. There's evidence that when we mulch with wood, which the arborist chips are, the biology in the soil favors plants that are woody. When we mulch with leaves, which are herbaceous, although fall leaves fall into the woody sort of category, the high carbon category.


Farmer Fred  15:02

Are they green or brown, right? I've had that argument for years, right?


Debbie Flower  15:07

The biology in the soil tends to favor plants that are herbaceous, which most of our vegetable crops are.


Farmer Fred  15:13

And ideally, if you have a healthy garden, would be to get yourself a little chipper shredder and shred up those plant parts too, and use that as a mulch.


Debbie Flower  15:24

I just got one for Christmas an electric one. And I use it. My son had one and I used it at his house and it was so easy. And it produced nice little chips.


Farmer Fred  15:37

And did you try running green material through it?


Debbie Flower  15:39

I didn't. Okay, I’ll have to do that when I go home and it stops raining. Yeah, so I asked for one for Christmas. My son lives in Minnesota. So I can't borrow it. But I asked for one for Christmas. And I got it.


Farmer Fred  15:51



Debbie Flower  15:52

Thank you. I'm all excited.


Farmer Fred  15:53

Yeah. Everybody should have a chipper shredder.  Because we all have green waste. Yes. And there's no reason that green waste should be tossed away. And the healthiest green waste you can apply, as long as your plants are healthy, is the the ones that you have in your own yard, as opposed to some stranger’s, right? Or Compost from wherever. Yes. Or mulch for that matter.


Debbie Flower  16:11

Sometimes the arborist chips bring you surprise plants.


Farmer Fred  16:16

Yeah. Especially if they chop down a liquidambar tree.


Debbie Flower 16:20

Yeah. All right.


Farmer Fred  16:21

So there's that. So, Joel, good question about nitrogen. And there are plenty of ways to keep it replenished. But you just have to keep at it.


Debbie Flower  16:30

And it is so interesting to hear your curiosity. I love it.


Farmer Fred  16:32

Thank you.


Debbie Flower

You're welcome.


Farmer Fred

I was thanking Joel.




Farmer Fred  16:45

Want to leave us a question? You’ll find a link at garden basics.net. Also, when you click on any episode at garden basics.net, you’ll find a link to Speakpipe in the show notes, where you can leave us an audio question without a making a phone call. Or, go to speak pipe directly: speak pipe dot com slash garden basics. You want to call  or text us? We have that number posted at garden basics dot net. it’s 916-292-8964, 916-292-8964. Email? Sure! Send it, along with your pictures to fred@farmerfred.com. Or again, go to garden basics dot net and get that link. And if you send us a question, be sure to tell us where you’re gardening, because all gardening is local. Find it all at garden basics dot net.




Farmer Fred  17:49

Here's a question that comes in from Felicia she's a little confused about what new soil to put in her new raised bed.

“Happy spring, Farmer, Fred! I am purchasing five raised beds from a local company and I need them filled with the best soil around. I know how important good soil is for vegetable gardening. I’ve asked on the local Facebook gardening group, but nobody told me exactly what type of soil to get they just told me where to get it. Everywhere I’ve checked, has all different kinds of soils and I am unsure which I should purchase. Can you help me please?”

And Happy Spring to you, too, Felicia!

That’s a tough question to answer, but here are a few guidelines:

You are correct that good soil for a vegetable garden is important for successful raised bed gardening. The definition of “good”, however, depends on whom you ask. Let me say right off the bat: anytime you create a raised bed with commercial soil, you are merely starting the process of developing “good” soil. The process takes years to improve the soil so that it has the microbiology and structure to feed that microbiology. It is not an overnight process, and you have to feed the soil year after year with what it needs.


You don’t say where you live, so this will be some general guidelines for acquiring a soil mix for raised beds.


First of all, try to avoid using garden soil from someone else’s property. Who knows what weed seeds and diseases it carries (more on that later). Even your own garden soil is risky, because of weed seeds and its composition (you don’t want a clay-based, rock-filled raised bed).


You have to determine how much of a soil mix you need for the raised beds. One handy mathmatical formula to remember: 27 cubic feet make a cubic yard. Multiply the width, length and depth of your raised bed, in feet. That will give you the cubic feet necessary for the raised bed. I would subtract four inches  from the height, because you will be amending that soil mix immediately with material that I’ll talk about in a minute. The finished product should be a soil levei in the raised bed frame  about an inch or two lower than the sides of the frame, plus that lower level will help you avoid runoff of water down the sides. And that that gap will allow you to install some screening on the top of the bed to keep cats out. I like to use 6-inch mesh hardware cloth/screens for that purpose. If your raised beds are four feet wide or less (which is recommended), then it’s no problem laying those 4’x5’ sheets (or that size cut from a roll of the wire), on the top of the beds. Cats don’t like tippy-toeing across those six inch mesh openings. Plus, that spacing on the screen allows you to more easily determine the spacing for your plants!


Consider how you are going to irrigate that raised bed. If it is by soaker hose or an inline drip emitter system, the “footprint” of the water from those emitters or hose will only be about 7 or 8 inches in diameter in new, commercial soil mix. In other words, the “cylinder” of water that penetrates the soil will be rather narrow in your first few years of existence. So, you might want to space the lateral lines of that system about eight inches apart. If you are going to use microsprayers, make sure the overlap of the spray of one head is about 50% of the adjacent sprayers’ throw.

You will have to water that newly filled bed more often in its first few years of operation because it will rapidly drain out.


Two other important considerations for that raised bed, before you add the soil mix: 1. incorporate a few inches of the new potting/raised bed mix with the existing soil that is under the raised bed. This will improve drainage. 2. If gophers are a problem in your area, laying down 1/2” mesh hardware cloth along the bottom of the bed and running it up the sides of the bed halfway can help keep the gophers out. Do that after tilling in that new soil with the existing soil.


No matter what soil mix you choose, you need to improve it every growing season with the addition of a green-derived compost (more on that later) and/or worm castings. This will improve what they call the “tilth” of the soil: improving its water holding capacity, as well as feeding the microbiology in the soil, which in turn, feed the roots of your plants.


Topping the soil with a few inches of an organic mulch (2-4”) year-round goes a long way towards making that new raised bed a winner. That mulch layer does a lot of good, including moderating soil temperature, helping to maintain even soil moisture, controls the number of weeds that might pop up, breaks up the force of the rain that can pummel a garden bed which can compact the soil; and, as mulch also breaks down, it feeds the soil and its microbiology! Mulch can be from any number of sources, including your own compost pile; chipped/shredded tree branches and leaves; shredded leaves from most healthy trees (not walnut leaves, though) gathered in the fall and chopped up with a mulching mower or string trimmer in a metal trash can. What about commercial mulch? Only if it has variable sizes, which is the beauty of chipped/shredded branches and leaves. The smaller stuff breaks down first, while the larger parts serve as the protective top mulch layer. Also, don’t pile the mulch right next to the stems of your plants. Give them a “de-militarized zone” of a mulch-free area for an inch or two to avoid rot issues.


I realize, at this point, you still have not received an answer to your hypothetical question, “How do I start this car?”, because my answer so far has been for the question, “How does an engine work?”.


If your final soil total need is basically several cubic yards, you might save money by getting those cubic yards from a commercial sand and gravel yard, especially if they are selling a blend intended for gardening. The safety of buying sterilized bagged materials, though, means you are not inviting any stray diseases into your raised beds, especially verticillium wilt, fusarium wilt and nematodes. After all, who knows where that sand and gravel company got their ingredients for their soil mix?


Another consideration: after you have filled your raised bed, do a pH test of the soil. Follow the instructions on the label. Make sure the pH of the soil matches the crops you are trying to grow. Most garden vegetables like a pH between 6 and 7.5. Blueberries, though, need a more acidic pH, around 5.5. If your pH results show a soil outside that range, follow the instructions usually included with a pH test kit on what to use to modify the pH to your desired number. And, it could take months for that change to take effect. As a result, whatever you’re growing in that first year may look a little sad.



If you are choosing a bagged potting mix/raised bed mix, read the label thoroughly for its ingredients, and try to buy locally produced soil products. If you are choosing your soil from a sand & gravel company, your best bet is choosing the ones that are intended for a home garden raised bed. You don’t want a heavy soil (clay, boo!), but a mix made of lighter components such as a mix/blend of  peat moss, coir, compost, mushroom compost, worm castings, sand, a silt-loam component, and/or forest by-products. But again, you’re taking a risk, because usually their silt-loam component is what they might refer to as "river-bottom" soil, which contains ??? Remember, too, that the pile you are looking at in the sand and gravel yard may not be the pile you get delivered to you, unless it is that same day.


If that sand/gravel mix is the choice you make, definitely do a pH test of the soil, and incorporate generous amounts of bagged compost and worms castings into the top of the soil. A tough thing to answer with a lot of bagged composts is: what is the source of the ingredients? For a garden, where you are growing annual crops, you want to use a green-waste based compost (not “forest-byproducts”). If, though, you will be growing fruit trees or woody, food-producing shrubs or vines, you do want that woody-based compost, such as forest byproducts. Different composts build up different soil biologies, depending on whether its a typical garden vegetable (no hard wood involved) or a shrub or tree. If you want to do a deep dive into that topic, Jeff Lowenfels has a series of books that begin with the words, “Teaming with…”, such as Teaming with Microbes, Teaming with Fungi, Teaming with Bacteria, etc etc.


As a final move, I might take soil samples of the raised bed mix and send them off to a soil testing service, so you can see what your new raised beds are lacking, in the way of nutrients. Three, reasonably priced sources for that test include the University of Massachusetts/Amherst, Texas A&M, and Colorado State University.


Thanks for bearing with me on this answer. Raised bed gardening is near and dear to my heart. And if it's one thing I've learned, it takes time to build up great garden soil.


Farmer Fred  28:14

Garden Basics with Farmer Fred comes out every Tuesday and Friday, and it's brought to you by Smart Pots and Dave Wilson Nursery. Garden Basics. It's available wherever podcasts are handed out. For more information about the podcast, visit our website, gardenbasics.net.  And that's where you can find out about the free Garden Basics newsletter, “Beyond the Garden Basics”. And thank you so much for listening.


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