DO YOU KNOW what it takes to grow a perfect root vegetable? When I recently asked readers and listeners what their most common seed-related issues were, one recurring theme surprised me: troubles with root crops, from poor germination of carrots, to radishes and beets and others that never sized up.

If you want to learn to grow any crop to perfection, call a person who grows them for a living, I figure, and better yet someone who does that in formal trials, where every last detail is recorded and evaluated.

Daniel Yoder (above), a research product technician at Johnny’s Selected Seeds in Maine, has a specialty in the world of root vegetables, and we talked about prepping the bed to reduce weeds before sowing roots crops; how to space and when to thin the seedlings; keeping them well-watered so they can bulk up; which are the easiest of each type, and more.

Read along as you listen to the Feb. 11, 2019 edition of my public-radio show and podcast using the player below. You can subscribe to all future editions on iTunes or Stitcher (and browse my archive of podcasts here).

Plus: A short 101 course on 10 top tips for growing root vegetables, also with Daniel Yoder, is at this link. (Below, gorgeous ‘KN-Bravo’ radish.)

root crop success, with daniel yoder

Q. Besides an education in plant science, I know your background includes both farming and research, so it’s a perfect combination for what you are doing today. Tell us just a little bit about your background and what led you to Johnny’s.

A. Yes, sure. It’s been a pretty natural progression for me. I didn’t really grow up on a farm, or gardening with my family or anything like that. It kind of came later in life for me, in college. I went to college for plant biology, and really gained an interest in both research and growing plants. I wasn’t quite sure which direction to take, but just a natural occurrence of jobs and opportunities brought me to working in both production and research. And I am really excited to be at Johnny’s now, doing things I used to do for fun—now I’m really getting paid to do what I really like.

Q. [Laughter.] And you get to work with one of my heroes among plant breeders, among vegetable breeders, John Navazio, who I’ve known for a long time and has helped me understand a lot of things about how plants grow. So that’s good, too.

A. Yes, John is a great resource here. He has taught all of us a lot of things.

Q. You grow crops with an eye to evaluation [above], not as casually as some of us might be doing in our backyards, where it’s a little more higgledy-piggledy [laughter]. And as I said in the opening remarks, I recently asked readers and listeners what was bothering them about things they grew from seed. Really, who knew? I was surprised at how many shouted out the root crops.

So maybe it’s good to kind of step back before we get into specific individual crops and sort of say, O.K., how do root crops function? What makes something a root crop, I guess—is there, like, biology, are they all biennials? What about them that we need to know to sort of understand them and start growing them better.

A. That’s a great question. I think once you really dig into root crops, there are endless crops that we haven’t even heard of in other countries—different types of potatoes, and Andean root tubers that you could really get into it. But I think the most common ones that you see in the garden, the brassicas—turnips and radishes—the beets, the carrots, parsnips, those are all pretty much true biennials in that they require a vernalized cold period, a vernalization, to induce flowering. And then once they’re done flowering, the plant then dies.

Q. So it doesn’t reproduce, it doesn’t set seed, until after that vernalization period happens, so presumably, in some climates that would be in the second year?

A. Yes, in some climates. It gets kind of confusing once you start moving around the different zones. With the varieties we have now, some really require very little cold period or even any at all—in radishes, for instance, so they might even go to flower and seed all within one year, even though they historically are a true biennial.

Q. Right. If we had to sort of rank some of the more familiar ones from easy to hard, by the degree of difficulty, is it like radish is the easiest and I don’t know what at the other end, rutabaga? [Laughter.] I don’t know what’s at the other end—parsnip is the hardest? Actually, I do think parsnips are hard sometimes to grow from seed. [Above, ‘Albion’ parsnip.]

A. I agree. Once you’re talking about the direct-seeded root crops, I think radishes are probably the easiest in my mind, and parsnips are the hardest.

Q. So you just said “direct-seeded root crops.” Is that one of the first tips you’re going to give us, that we’re direct sowing, that because it’s a root crop, we don’t want to transplant it, we want to direct sow it?

A. Yes, that’s a great point. There’s been some growers who I’ve heard have success with beets, that they can transplant beets.

Q. I’ve heard that, too.

A. You still want to get them in as early as you can, just so they don’t have too much restriction within the cells. But pretty much all the other root crops, you’re going to want to direct seed or you’re going to run into issues with root stunting.

Q. So they resist having their root disturbed early in their little lives.

A. Yes, definitely.

Q. Some of the questions that I was asked, a reader named Caroline said, “I have a really hard time getting carrots to germinate,” and she’s even tried pelletized seeds. But she feels restricted by that because she’d like to grow different varieties. Maybe we should start with carrots and talk about just a little bit … and John [Navazio] and I years ago had a really great conversation about how to grow carrots.

When we’re direct sowing, are there things we can be doing to get our root crops to do better and what’s the basic protocol that you’d recommend? And then we can sort of do offshoots into specific ones that have extra-special needs, maybe.

A. That sounds good. I would start with, in roots crops in general, I think some of the basic principles are very similar to all crops:

You want full sun all day long. I feel like I run into many times where gardeners have a little bit too much shade in their garden and if you can try and find a sunny area.

And then spacing, of course, with the root crops is pretty important.

Back to germination, I think what’s really important for root crops is getting your beds established. A lot of crops you can get away with transplanting or direct seeding and maybe the seeds are bigger, like beans or peas and corn, and you don’t really need a very well-prepared bed in a lot of cases, for those crops. But for these root crops you really want to focus on making sure to have a loose, friable bed. There’s a couple of tricks I usually give at this point but-

Q. I love the tricks; we love tricks. Oh, no, no, no, go for it. Yes, we love the tricks. [Laughter.]

A. So you want to make sure you can loosen up your soil, if you do have a heavier soil, especially. If it’s not well-drained you might even want to raise it up, even just a couple inches is usually fine, just to get a little bit better drainage in your soil.

You can pick out the rocks, especially in the row, if you’re able to, with just a typical hoe. So I usually do that, especially for carrots.

Then one big trick that a lot of people don’t think about is making sure you pre-irrigate your beds, because you want that water to get down below the top layer, which is hard to do, especially for carrots, when they’re germinating—it’s hard to get that water below them, because you don’t want to water them too heavily while they’re germinating. So you want to pre-irrigate.

And you also want a firm … If you’re going to make a raised bed you don’t want to loosen it and just plant into a loose bed, because that bed will settle a little bit, which will also kind of distort the root growth a little bit, and kind of just set them back. So firming the bed to get really good seed-soil contact and better straight root growth is pretty important.

Q. So we’re going to pre-irrigate so that … We’re going to prep it. We’re going to get rid of … I mean, some people use bark chips and stuff; that’s another terrible thing. I can’t imagine why anyone wants to use them.

A. [Laughter.]

Q. But between rocks and bark chips, things like that, we got to get them out of there for these little babies. And we’re going to pre-moisten. We want the soil to be a good texture without a lot of lumpy-bumpy stuff, and well-moistened.

So it’s not super dense and packed down. It I raised it up a little bit and then I want to make sure I kind of tamp it down a little bit before I sow, is that what you’re saying? So it’s not too lofty and then it collapses on the seeds, is that the idea?

A. Correct. Yes. And also, the seed-to-soil contact is really important. When you firm up the soil a little bit it gets rid of some of the air that’s in there, so if a seed takes a little while to germinate there might be a little bit too much air around the seed itself and it helps to have that tight soil contact to get the moisture right to the seed.

Q. So I might make a, with a tool or whatever if I’m just in a garden setting and I might be doing a short row of something, I might use my finger or a bamboo stake or an edge of a tool or whatever. I might make little very small … would I be making a furrow and then covering the seed, in this pre-moistened area? What am I doing?

A. That’s a good question. If you don’t have any kind of seeding implement…

Q. Right! [Laughter.]

A. …I would go with making a furrow. If I’m planting by hand I like to, especially for these smaller root crops, is to plant them in maybe a 2-inch band, a 1- or 2-inch band, just little bit of width so that you can get a few more roots in. So I typically sprinkle them a little bit across that 1 or 2 inches.

And then one trick, if you don’t have … One trick for carrots, especially, is adding something that’s a little even lighter material on top, like a sand or vermiculite or peat moss, mixed into your soil, to cover them. And that will give them less chances of crusting soil and things like that.

Q. It may have been John who recommended to me, if I was having trouble with the soil crusting before the carrots or other roots crops germinated, maybe to put a moist piece of burlap over it when I was done sowing—obviously, before they came up, but just to keep things from drying out.

A. Yes, definitely. And it doesn’t have to be wet before you put it down. You can just irrigate it, and some people use that frost protection, the row cover material.

Q. Oh, sure. O.K. That’s good.

A. And that works just the same as burlap.

Q. And that’s really light and easy to work with.

A. Yes, and it lets the light through, too. I’ve heard of people putting wood down on top of the seeds, which does a very good job of keeping the moisture in there, but you got to watch that you pull it up at the right time. The burlap lets the light through.

Q. Right. You were talking about a 2-inch, a thick band. In that band, how many seeds are we getting in how much space? Make me a visual of that if you can, and tell me if it’s different for different root crops, in terms of how thickly I’m sowing.

A. Sure. It does get a little technical with the band method. It’s not for everybody. But if you are trying to increase your yield I think that would be my recommendation. And it is different for different root crops. So you’re really trying to get whatever your target in-row spacing is, you can plant the seeds within that band. So if you’re planting radishes and you want to get them at least three-quarters of an inch apart, they can be staggered in that band, basically, to get more radishes in.

Q. O.K.

A. But I would shoot for your target in-row spacing. I wouldn’t plant them too densely.

Q. O.K. So it’s not like if I’m going to plant peas in a big band, so to speak, I might plant them even more thickly—peas is a different matter—but with this I’m still going to respect the recommended packet spacing within the row, if it says three-quarters of an inch apart.

A. Yes.

Q. So then, what about thinning? Because I think a lot of times a lot of the packets say, thin after blah blah and eat the baby greens. But isn’t that disruptive? When is thinning O.K. or not O.K.? Is it better to plant, as your farmers say, “plant to stand”—plant to the actual exact spacing. How do we go about that?

A. There’s a lot involved with that as well. Going back a little bit, I think I would start with what seeds do I have and are they a couple years old? Are they new? Do I trust the quality? When I’m planting, especially carrots, I think there’s, and even in the colored carrots you start to see some lower germination rates just naturally in those types of crops. So you want to check, if you can, check your germination rate, think about if it’s new or not.

Planting to stand, I think, is not really a great suggestion for beginners until they really have a little more comfortable idea. But it’s a great thing to keep in mind still, that you don’t want to just put down a lot of seed because it’s quick and easy. If you take a little extra time to put down closer to your appropriate stand, it’ll save you way more time later on with the thinning process.

Q. O.K.

A. So then, getting into your thinning techniques question: I usually wait until they’re big enough that you can easily grab them with your hand. I think for rutabagas and turnips, in particular, I think they’re a little pickier, and I wouldn’t wait too long on them because they really seem like they need their space to size up early. But I think radishes and carrots are a little more forgiving. Radishes, maybe still, at first true leaf.

Q. Oh, so radishes you’re really thinning early. What about beets? [Above, ‘Chioggia Guardsmark’ beet.]

A. Early. Did you say beets?

Q. Oh, yes, beets.

A. For beets I think the same as radishes. I would get them pretty early.

The one difference I think is with the carrots and the parsnips. One thing I usually do is, since they are so slow to germinate, especially in the spring you can have cold soil, so you want to make sure that all your seed comes up so you don’t have to keep going back and re-thinning, or realize that you didn’t get all the seeds. So I like to wait until they’re a little bit bigger. And it also kind of helps with some of that early weed control, if you have a little bit thicker stand before pulling them.

So I usually let them just get 2 to 3 inches or so. They don’t have any root development at that point so it won’t disturb them.

Q. A reader named Becky said her failure is “radishes that fail to fill out;” it keeps happening for her, and she keeps trying. And she knows she must be doing something very basic wrong but on the other hand, right next door in the same bed her “Swiss chard is a roaring success” and so forth.

And Mary Sue said she’s tried beets for two summers. The first year she got “a couple of decent-sized ones, but really they never reached their full promise.” And she’s wondering, both of them are really wondering: Even though the soil conditions are good and other crops in these beds are growing well, what else is involved in a root crop shaping up?

We’ve talked about some of the things, like thinning, when to thin, spacing. I mean, I’m assuming if you put them too tightly spaced together they couldn’t make a full root. It would be an impediment, wouldn’t it?

A. Yes, I would agree with that. Spacing is one of the key things that you would want to make sure you get dialed in. I’ve seen over and over again people with a fear of thinning, and I’ve gone through it, too. [Laughter.]

Q. Of course.

A. You don’t want to kill your plants.

Q. Of course, yes.

A. But once you see the difference you’re sold immediately. I would start with that. Sunlight, like I said.

Q. Sunlight. O.K., good, yes.

A. And then I think what’s different about the root crops is, to really get them to size you want to make sure you …. Some of them don’t need a lot of water in the beginning, but they do want consistent soil moisture, especially when they’re starting to swell.

Q. Right.

A. So you could even go out and check on them. If you’re not sure when to start giving them that consistent water, it’s probably best the whole way through but especially when they’re starting to swell.

Q. And sometimes that is, in many of our areas, at the driest time of the summer. You know what I mean? It can be during a hot spell and there may not be a lot of natural moisture, so we’ve got to keep up with that.

A. Yes, yes. I think a couple things. You can, for carrots, for instance, you could mulch them or you could hill them. The hilling does a couple things. It keeps the shoulders from greening. It also keeps more moisture in the soil.

Q. And I assume this isn’t a hill the size of a potato hill; this is a little hill, a mini hill. [Laughter.]

A. Just a little hill, yes. Only an inch or 2 is all you need.

Q. How interesting, though. I’ve never heard of that. Huh. That’s interesting. That’s very interesting. Some of these are different, like beets. The “seed” in the packet  [below] isn’t really a seed, is it? I mean it’s almost like a pod, a fruit, I don’t know what it is technically, but do you know what I mean?

A. It’s a bunch of seeds melded together, basically.

Q. So that affects spacing. That’s a little bit different, right? Because no matter how we space the “seed,” that we get, each thing that comes in the packet, it’s still going to make a cluster at each point if they all germinate, right?

A. Yes, and some of it changes depending on how the seed has been harvested and processed before it comes to the home user. Some of your heirloom seed, or even if you’re saving your own seed, you can get clusters of, I don’t know, five or six seeds in a cluster. A lot of the seed that’s gone through cleaning, that would come to us and we would sell, I think has been broken up a little bit.

Q. I see.

A. It might be two or three. And then you can even buy separated seed or genetically singulated beet seed. But that’s a little different.

Q. I want to talk about some sort of varieties, things that if I’ve never done well with carrots, what are the easiest kinds of carrots to grow? Is it the sort of stocky, shorter ones or the little round … Do you know what I mean? And similarly with these other crops. Are there any sort of beginners, to get my confidence up with root crops in each species?

A. Yes, definitely. I work mostly with radishes and carrots so I’ll probably give you my best recommendations in those. With carrots, I think you’re right, those shorter, stocky ones are kind of a little more bulletproof. They tend to work well in all types of soils. Some of the short Chantenay type carrots are a little more sensitive to bolting. But those are generally really good ones to start out with.

Q. O.K.

A. If you’re planting in the spring, I feel like most people get most of their seeding done in the spring rather than fall, which a lot of these crops do much better planted in the summer towards fall, because they like to mature in the cold. But if you’re planting an early carrot I would go with one, we carry a bunch of early, what we call early Nantes carrots, which are better for spring because they put on some bulk and flavor at an earlier time, so that don’t have to wait for them to size up while it’s starting to get hot out. So something like ‘Yaya’ or ‘Napoli,’ I think, are really great ones if you want a little longer carrot for the spring.

And then for radishes, I was really surprised once I started growing a lot more of the storage type radishes, the daikons and watermelon types. But specifically the short daikon radishes compared to even your early spring French Breakfasts and round reds. Those are easy to grow, too. But these … like the ‘KN-Bravo’ [photo higher up the page] and the short, stocky daikons are almost a bulletproof variety in all seasons [below, ‘Alpine’ daikon]. And I would recommend that to anybody who hasn’t thought about it, to try those alongside their spring radishes.

Q. So, last minute, want to put in a pitch for those colorful carrots that you mentioned, because boy, they are beautiful. Tell me which ones I should be looking at.

A. Yes, sure. There’s a bunch of new stuff coming out. There’s a lot of breeding going on in colored carrots now, so they’re a little behind orange. So you never know what to buy—a lot of them are bolty or don’t size up very well or are hairy but-

Q. Hairy. [Laughter.]

A. …there are a couple of new ones.

Q. I know I get that.

A. Typically the hybrids are a little easier to grow, more consistent. ‘Gold Nugget,’ or ‘White Satin,’ ‘Purple Haze’ [below] are pretty good spring-planted varieties that I would recommend.

Q. So root crops: We’ve got to be mindful to pre-water those beds, prep the soil. We’ve got to space well. We can’t be afraid to thin. [Laughter.] Keep them evenly watered. And is there any big fertility thing? I forgot to ask that, just real quick.

A. Oh, yes. I think you just want to watch for any crop, you don’t want to over-fertilize, especially in the beginning so that crops. It could cause a radish to be too leafy and carrots to get hairy, so just a nice, slow fertilizer or compost.

Q. Well, Dan Yoder, I’m so happy to speak to you and to finally make your acquaintance and keep up the good work and I hope I’ll talk to you soon again. Thank you.

A. Thank you. Likewise.

more on growing root crops

• The short course: 10 top tips for growing root crops with Daniel Yoder
• How to grow carrots, with John Navazio of Johnny’s
• How to grow beets, with Brian Campbell of Uprising Seeds
• How to grow Andean tubers

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 ninth year in March 2018. 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 Feb. 4, 2019 show using the player near the top of this transcript. You can subscribe to all future editions on iTunes or Stitcher (and browse my archive of podcasts here).