up your seed-starting game, with seed-mad joe lamp’l (aka joe gardener)

WHAT REALLY MATTERS when we start seeds? What tweaks to our process or gear can actually move the needle from so-so results or worse, to closer to pro? My friend Joe Lamp’l wondered that, too. He undertook batch after batch of experiments (that’s his seed-starting room in action, above, and his shoes in the foreground) to test a lot of the conventional wisdoms out there, many of which conflict with one another, by the way. And I couldn’t wait to hear what he learned that we can each put to use in our own pre-spring seed-starting adventures.

You probably know Joe as host of the popular PBS series “Growing a Greener World” and the Joe of joegardener.com website and podcast. He’s also creator of OrganicGardeningAcademy.com, with a suite of online classes, including one about to debut on seeds. We talked about lights–he did 14 different lighting trials to try to determine which kinds are “best,” where to position them and how long to run them each day–about watering, about essential gear to make it all run smoother, and more.

Read along as you listen to the February 3, 2020 edition of my public-radio show and podcast using the player below. You can subscribe to all future editions on iTunes or Spotify or Stitcher (and browse my archive of podcasts here).

seed-starting ‘ahas,’ with joe lamp’l


Margaret: How are you, Joe? … I’m surprised you have anything left in you after trialing all those damn seeds. [Laughter.] So, oh, he’s giddy boy.

So you’ve been growing from seed confidently, or at least I thought so, for years. And then you sort of went wild this last year with these extra trials and I mean, I would look at your Instagram photos and videos and you were like in this jungle of seedlings and there was somehow, however, a method to the madness.

So tell us the truth. How many seedlings did you grow and explain sort of the mad-scientist process that went into preparing to do this course on seeds?

Joe: [Laughter.] I think I’m as guilty as anybody when my exuberance and over-enthusiastic nature takes over. So I lost count of the packs of seeds that I had, Margaret, and each seed packet has a minimum of 25 seeds. So I would say I was in the neighborhood of a couple thousand seedlings every round of trials, so about 52 to 60 seed trays, and each tray had at least 18 cells and some had 72 cells. So you can understand why I’m a little delirious. I sort of lost count and got lost in the jungle, but it’s not a bad thing.

Margaret: So were there parts of the seed-starting process that you were particularly determined to sort of get to the bottom of, like things that had maybe stymied you year after year, or that were just super-confusing? Like in five different resources or different books or online sites, you’d see five different recommendations? Were there certain things you were trying to figure out in particular?

Joe: Yes, a couple in particular. And one certainly was the lighting. Lighting is continuing to evolve and with the LED grow lights, it’s not just that they’re LED anymore—it’s what spectrum of LED light do you want, and how strong do you want it, and how high do you hang it? And how do your plants respond, and is it worth it to spend all that extra money on a super-powered LED light if you’re just growing seedlings to put outside six weeks later? I mean, I had so many questions and that’s the thing, I’m such a curious gardener myself. I just feel like I’ve got to know everything and why not share it with the rest of the people once I find out? I say I’m the crash test gardener.

Margaret: [Laughter.] Oh, boy. Speaking of light, so we can start there. So a number of years ago, Dr. Thomas Bjorkman of Cornell, he’s a crop physiologist who studies the effects of environmental stimuli on plant growth and their development, particularly in vegetables, and that’s his whole career, and he has a laboratory. And his specialty is vegetables, vegetable seedlings, like the physiology of how they grow and how can we do better with them and so forth. And he advises the nursery and farm agriculture industries.

He told me that in the home seed-starting environment, the Number 1 thing we can do to improve results and especially prevent leggy seedlings is to improve the light. And there’s just a lot of other factors that affect how seedlings develop, but that the light was the thing. And he was like, “Margaret, no. Tell all your people, even though the windowsill looks bright, it’s not bright. And tell them that the old fluorescents are a lot less light than the T5s.” And now he would say, “And the LEDs.” [The entire interview with Dr. Bjorkman.]

But what did you end up kind of… Did you come to a conclusion about light? Because I mean, clearly I’m on the fence. You can hear it in my voice. I’m not changing out my T5 fluorescents, which have mirrored what would you say, reflective interior?….the interior of the hood is reflective so you get a little extra light. And I do really well with those. And I did well with regular fluorescents for a million years–a shop light–for a million years before that. But I don’t know.

What did you try and what are you feeling about it? Because I know you had crazy pictures of like… Is this your basement or where is this place that you do all this? [Laughter.]

Joe: I call it my seed-starting room [photo, top of page], but it’s just I guess the breezeway from going down into the basement and heading out to the door to my garden. So there’s this about 10-foot-wide space and it’s probably about 25 feet long. And so that’s my laboratory for starting all these seed trays, and it’s right outside my office. And so the challenge for me is trying to get through that area without getting distracted and getting sucked into the world of watching seeds germinate. [Laughter.]

I’ll stand there for 10 minutes, just seeing if I can notice a seedling move just because it’s grown a little bit in those 10 minutes that I was there.

But to your question, I did 14 different light trials and so I tried every type of… Not every type of light there is, there are so many out there, but I went from the classic old-fashioned, old-school shop light; to the shop lights with the LED inserts, to shop light LED lights that all come together as one unit so you can’t change out the lights—you get what you get.

Joe: I varied the light spectrum of the fluorescent tubes. I went from a low Kelvin [scale] at 3,000 to a high Kelvin at 6,500 to test color temperatures. I went to the LED lights, and I went to the type that has just what appears to be a clear white light, which is just what’s called full spectrum, which is all the frequencies that the human eye sees. And I did dual-band LEDs, which is focusing on the red and the blue, which we now know plants respond best to from a vegetative standpoint. So I trialed those against everything else.

And then the grand finale was, I splurged for a really expensive LED ful-spectrum grow light that costs $300 and it was 2,000 watts. And I’m like, wow, this is a big light. And it really was, it was 48 inches long and 20 inches wide. So it covered the whole shelf.

And so over multiple trials, I put them all up against each other, head to head. And if you’re asking for my conclusion, it’s fascinating because on the super-expensive grow light, it really does perform uniquely. And if you’re trying to have things go to fruit or flower indoors, you need a light like that. But if you were just trying to get seedlings coddled along for four to six weeks inside, whatever lights you have can work.

What I learned, Margaret, is that you just have to learn how your light works with the plants that you’re growing underneath them, and learn how to position those lights over the plant,and learn how many hours a day you need that to have that light on. And how does that plant get the optimal amount of light coming out of what you have? So you don’t necessarily need to go buy one, you just need to understand a better relationship between the light and the plant and how to get the most out of both.

Margaret: Right. And I’m just like, if we had some sound effects, I would go “Ding, ding, ding, ding.” I’d love that answer, right? [Laughter.] Because, again, I’m an old gardener, and 40-something years ago I was using shop hood with one cool light and one warm white fluorescent tube. And I mean, they hardly put out anything if you compare them to the sun outside on a day in May, when seedlings would germinate themselves in nature, as Dr. Bjorkman again at Cornell explained to me. But it’s a lot of light if you know how to use it. And the things that you have to know is how warm is what’s being emitted from that tube? So how close can you get? Because you want to get close but not so close that you toast the babies, or cook them. You know what I mean? And the LEDs are cooler, aren’t they? They don’t have the heat emission? Is that the case?

Joe: Right. So they’re considered more efficient. So for whatever wattage they are, they’re considered more efficient because when the power is coming out of the light, it’s going to two places. It’s going to put out the light, and it’s going to put out heat. And so the less heat, the more light, and vice versa. And LEDs do a better job of being more efficient in that they’re putting out more light. But what we often misunderstand about those lights is that we think brighter is better, and that plants perceive light the same way we do, but they don’t. They respond completely differently. So just because a light is brighter doesn’t necessarily make it better.

Margaret: Right. So, again, I’m feeling happy with my… I don’t know if they’re five- or seven-year-old T5s. I’m not talking about that I’ve been running them, the same bulb, necessarily for seven years nonstop. Because again, I might use them for six weeks, 12 hours a day, right, once a year for that little period, because I’m overlapping a bunch of different crops, but that’s it. I’m not doing a million things. I’m not doing as many, 52 trays times a billion seeds like you did.

Joe: [Laughter.]

Margaret: And obviously you change out the bulb when the bulb is… You have to read the instructions and see what the life of the bulb is.

Joe: Yes, and-.

Margaret: Yes, go ahead.

Joe: Well, I was going to say, I mean, if you really wanted to geek out on that, there’s an instrument that you can get that measures that light quality around your plants. It’s not for the everyday seed starter who doesn’t want to invest a minimum of $150. But there are tools out there, which I invested in because I was determined to really measure the details, and that’s one way that you can do it is those light readings go down as the bulbs get older and that’s one indication, but probably not the most practical things for people to do.

But using your eyes and looking at how the plants respond will really give you lots of clues. You might not be able to detect it in the perception of the brightness of that light to the human eye, but your plants will tell you. It’s amazing how much they’ll tell you if you just learned to communicate with them.

Margaret: So roughly speaking, I mean, like that big $300 bulb that you got or whatever, that was probably higher above the plants than-

Joe: Yes. I couldn’t get it high enough, Margaret. Instructions that came with it said, “Start off with the lights 24 inches above the plants.” So I did that and initially I got picture-perfect seedlings. But the longer those seedlings were under those lights, the more they showed that they were uncomfortable. They weren’t responding as you would expect; they weren’t filling out. It’s almost like they didn’t want to grow anymore. They didn’t want to get any closer to the light. So that’s an example of paying attention to your plant response to the light.

And so I raised the lights up and the plants responded favorably to that. But as the plants got taller, they again kind of shut down. And then they showed other symptoms that told me the light was too bright. And so the bottom line on that, Margaret, I just couldn’t get the plants far enough away from the light.

Margaret: Right, not in your home environment, in this seed room. Yes. Yes. So a lot of listeners probably have either plain fluorescents in a shop hood or like I have, the smaller, more higher-output fluorescents, the high output fluorescents like T5s. How close or far away would you say those would be? Because I’ve always kept them within a couple of inches of the tops of the plants. Do you know what I mean?

Joe: Yes. Right, exactly. So it depends on the light of course. But a HO T5 [high output T5], which is what you have, doesn’t sit as close, should not sit as close to the tops of the plants as the traditional fluorescent, because it does put out a little more heat and it is more efficient. So you can’t tell that from looking at it, but you will tell from the plant response. So my sweet spot above the tops of the plants on my HO T5s was about 6 inches above-

Margaret: Six, cool. O.K., great. I’m happy to know that.

Joe: … the top of the foliage, which is about 5 inches higher than the fluorescent, the classic T12 fluorescent lights.

Margaret: Right, which are really close. We put those really close. Yes. So O.K. So let’s just move on. I mean, there’s lots to learn and again, you’re going to have this whole course coming up and we’ll tell people about that, that includes more enlightening I’m sure. But just so we don’t use up all our time on lighting.

I mean watering is another thing that confounds people and also can cause a lot of problems, and especially the combination of, I think, and again, this was from the doctor, the professor at Cornell and he was like, “If you’re using a heat mat, a propagation mat,” he said, “the reason they call it a germinating mat is it’s only for germinating. Get the seedlings out of there the minute they poke up. And get that dome off. Don’t cook them.” Especially get the heat mat out away if you’ve got that dome on, because you’re causing this horrible conducive to disease, etc., like steam bath, right? I mean it’s…

Joe: That’s right. He’s saying all the right things, but that heat mat is there just to aid with germination and it speeds up the germination time by anywhere from a day to several days, because plants have an ideal germination range. And if you can get the ambient temperature or the soil temperature to closer to that range that they prefer, they’re going to germinate faster. But once they germinate, I remove those humidity domes right away because if you don’t, you trap too much humidity around the base of the plant and then they’re subjected to a fungal disease called damping off. And that’s the Number 1 killer with young seedlings and it comes from too much moisture around the base of the plant. So, yes.

Margaret: Right. So it’s not like we want to have them in like this terrarium, for goodness sake. Right, right? Like no. N-O.

Joe: [Laughter.] Right, not ferns, probably.

Margaret: But you see pictures all the time online and stuff of like seedlings growing in these… Again, it’s like a terrarium with the hood on and it’s crazy.

Joe: Yes. That’s not best practices for starting to seedlings.

Margaret: By contrast, I see in your pictures you got fans going in the place, don’t you?

Joe: Absolutely. For the very reason of helping to ward off that condition of damping off, because if you can keep air moving across the base of the soil, right where those seedlings are, you greatly reduce the risk that you’re going to have any sort of fungal disease. Plus air circulation, period, is good to have around plants and so it doesn’t hurt to have those fans there. I highly recommend it. I put those on the must-haves list of things that you need when you start your seeds.

Margaret: And they’re not on high, like blowing the plants over. It’s just kind of moving the air gently around the room?

Joe: Right. If you can see the seedling on the far end of your seed tray, barely moving, that’s enough. So I have my fans on low setting. They’re small, tiny little fans.

Margaret: Yes, I saw that.

Joe: Yes, but I just like to see that the air’s moving across and I know that that’s enough to do the job.

Margaret: So watering then, where I derailed from, but do you use capillary mats below your seedling trays? Are you hand watering… What are you doing? Are you misting? What was your decision about watering?

Joe: [Laughter.]

Margaret: {Laughter.] Uh oh, this is a mess. I can tell this was a crazy experiment.

Joe: Oh yes, that was definitely part of the trials. I wanted to compare top watering versus bottom watering versus self-watering capillary mats. And the top watering, it depends on the types of lights that you’re using, first of all. If you’re using those fluorescent lights that sit right on top of your plants, it’s really hard to top water or water overhead.

Margaret: You got to move the tray out.

Joe: Because you just can’t get to everything. Plus you’re beating those little seedlings down when the water droplets hit it. So I prefer to bottom water, which is just pouring water into a solid tray that the seed tray nests into. But the problem with that, Margaret, as you probably know, is if you bottom water, there is a level of water in that bottom tray. And if the seed tray is nesting into that, then you have a portion of your root mass or your soil sitting in that water too. And some of those roots can just be underwater and drowning.

And so although plants, young seedlings, love water and they respond to it well, too much water can cause them to respond too quickly to the growth, and they get out of proportion and they become too tall and too soft relative to their girth, and they can snap and break. That’s one reason why I don’t just bottom water.

And the other thing is plants respond worse to over-watering than under-watering. So it’s better to err on one side than the other.

Margaret: And seeds need water to germinate more than seedlings need as much water. Like once they’re up and growing, you want to back off a little bit. You don’t want to wilt them. But seeds, on the other hand, you dry out a half-germinated seed and you kill it.

Joe: That’s right.

Margaret: Do you know what I mean? So it’s wetter before germination, and it’s less wet and more careful with your timing of your watering once it’s up, I think.

Joe: Absolutely. There’s a sweet spot to how much moisture should be in that soil to initiate germination within the seed, because the seed needs that and air for this exchange that takes place in the seed to kick off the germination, but it needs that moisture, for sure.

Margaret: Yes. So did you end up tossing anything or buying anything that you were super glad… I mean, you bought a lot of different things, but is there something that you’re going to use every single year from now on because it’s just the greatest thing ever? Do you know what I mean? Any piece of gear that will now become a standard or…?

Joe: Yes. Yes. Margaret, how do you hang your grow light over your seed trays? What do you use, a chain or do you use those ratchet pulleys?

Margaret: Well, my incredible neighbor, Tom, who’s a master carpenter and used to build Steinway pianos, he made me this fabulous thing that adjusts on pulleys. Yes, and I bet you’re using something like that.

Joe: I am. I’m using those ratchet pulleys. Where I used to use those small chains with the S-hooks all the time, and every time-

Margaret: [Laughter.] Yes, oh my goodness.

Joe: Yes, Every time the plant grew, you had to mess with the chains and then-

Margaret: And try to get it level.

Joe: Right. And good luck on that. And good luck trying to keep that S-hook from coming detached and the lamp falling into your plants and crushing your seedlings. So what changed my life a few years ago were those ratchet pulleys, that on a thin cord, you just tug on it lightly and it click, click, clicks up the lamp; super-easy. And when I show people that, it blows their mind. It’s like they’re game-changing.

Margaret: And It’s not expensive. It’s not a million dollar thing at all.

Joe: No, it’s not. And there’s one other piece of equipment: I love my dual timers, which has basically eight outlets in it, two strips of four. One side is powered 24/7, so it’s not impacted by the timer. The other side is directly related to the timer. So in other words, you can use that one strip of power outlets to drive your timer-sensitive things like your grow lights. And then the other side has your fans and your heat mats or whatever else you have plugged in that you don’t want to necessarily go on and off during the days.

Margaret: Well, what I’ll do is I’ll get for with the transcript of this conversation, I’ll make sure to get the ones that you’ve had good success with the proper links if people are interested.

Joe: O.K., good.

Margaret: Yes. Did you have any like big aha’s about timing or anything else that, do you know what I mean, that’s not gear-related but it’s just…?

Joe: I did, first of all, timing with the lights: I think more people than not leave their lights on about 16 hours a day. And that’s a good rule of thumb. But again, it depends on how much light is getting to your plants over a 24-hour period. That’s really what you need to find out. And there’s ways that you can do it beyond the scope of this conversation. But in general you can do it 16 hours.

But I did find that when I left the lights on for 24 hours a day with a reasonably bright light, it was more light than the plant wanted. And it showed me that in ways that it just kind of shut down and it wasn’t as vigorous as my lights that were getting more time of darkness. And so timing there was one thing. And then the other thing is I think we get so anxious to start our seeds in the wintertime because we just want something to do and-

Margaret: [Laughter.] Don’t we?

Joe: Yes. But we tend to start our seeds a little too early. But when you had those seedlings growing over a four- to six- to eight-week period, the longer they’re in that artificial environment before you can plant them outside, the more stressed they become. Because they’re not getting what they need as they get bigger that we can provide indoors. And so I think it’s important for people to understand timing of how long they really think is realistic for their plants to be inside before they can take them outside, and try to resist the urge to start too early.

What I concluded for sure, again, it’s better to start a little bit later than a little bit earlier.

Margaret: I’m happy with a six-week tomato seedling, that’s a little shorter and stouter, than I am worrying in those extra two weeks indoors for an eight-week seedling that it’s going to go amiss. Do you know what I mean? [My seed-starting calculator tool: Calculate when to start what for your zone.]

Joe: I know exactly what you mean. And then the plant fully takes off outside once it gets the opportunity.

Margaret: Absolutely. So I wait later than a lot of people wait where I live. So tell us: all of this experimentation is going to lead to this course, Master Seed Starting, I think it’s called.

Joe: Yes.

Margaret: You’re taking registration now? Around the end of January in 2019 when we’re playing the show? [UPDATE: After a strong early response, the course registration was closed till the weekend of Feb. 8 and 9, and probably will open again for a couple of days a week after that as well.]

Joe: The course launched today, Margaret.

Margaret: And so “today” is that we’re taping this show is the 30th.

Joe: Yes.

Margaret: O.K. And so people sign up and then they take it at their own pace. Is that what the case is?

Joe: Yes. And that’s the beauty of an online course. You can go anywhere to take it and you take it at your own pace and you have it forever so you can refer back to it. And then when we update, you get those updates free too, because we keep it current. Things are changing, but we want to keep everybody current as well. And so online courses provide opportunities that books just can’t do. You and I are both authors and we love our books, but-

Margaret: Right. But once it’s put to bed- [Laughter.]

Joe: … it’s the technology of an online course. Yes.

Margaret: Yes. So all right. So obviously with the transcript, I’m going to give the links to all that so people can explore, find out if they want to participate.

You’re in the Atlanta area. Have you started any seeds yet? Not for your crazy experiments, but for this year’s garden?

Joe: [Laughter.] You know, that’s a great question. Besides the ones, the thousands that I’ve started already for the course, I have to start around March 1st. I’m going to give myself a breather and start March 1st. I had a momentary thought. I’ve just taken a break this year, now that I’ve done all these seedlings, I can’t do it. I love starting seeds and so I’ll be back at it March 1st.

Margaret: [Laughter.] O.K., well Joe Lamp’l, now the creator of Master Seed Starting course in addition to all his other accomplishments, “Growing a Greener World” and books and JoeGardener.com and the Joe Gardener podcast. Thank you so much for making the time. And I’m not laughing at you. I’m laughing with you because I know how it feels to be crazy about plants.

Joe: [Laughter.] We’re two peas in a pod, Margaret.

Margaret: I know we are, separated at birth–separated at germination. [Laughter.] I’ll talk to you soon, Joe.

Joe: All right. Thanks.

(Photos from JoeGardener.com, used with permission.)
(Disclosure: As an Amazon Associate I earn from qualifying purchases.)

more on successful seed starting

prefer the podcast version of the show?

MY WEEKLY public-radio show, rated a “top-5 garden podcast” by “The Guardian” newspaper in the UK, began its 10th year in March 2019. In 2016, the show won three silver medals for excellence from the Garden Writers Association. It’s produced at Robin Hood Radio, the smallest NPR station in the nation. Listen locally in the Hudson Valley (NY)-Berkshires (MA)-Litchfield Hills (CT) Mondays at 8:30 AM Eastern, rerun at 8:30 Saturdays. Or play the February 3, 2020 show using the player near the top of this transcript. You can subscribe to all future editions on iTunes/Apple Podcasts or Spotify or Stitcher (and browse my archive of podcasts here).

  1. John Moore says:

    Thanks for the timely and most welcome show! I appreciated hearing that the transition from shoplights to T5s set you a bit back on the learning curve, too. I did it three years ago but it took this long to learn optimum light heights and timer settings. Your conversation was a confidence builder.

    1. margaret says:

      Thanks for letting me know, Lauren. It seems to have gone dead…was working earlier! Have put in a call to the radio station engineer and it seems the hosting company had a server issue that hopefully is fixed now! :)

      1. Lauren? says:

        THANKS! I enjoyed it. When I was an art teacher I also took autistic students to work in a nearby greenhouse. The Amazing lady who ran it had some very unique ways to start seeds and I have adopted everything she said to do.

    1. margaret says:

      Hi, Rhonda. I emailed to ask. He says: “The light intensity tool is a PAR / PPFD meter. It measures Photosynthetically Active Radiation. They cost from $150 and go way up from there.” He has this one and says of course the $350 ones are probably even better, “but it works.”

  2. Craig says:

    Very timely post, even if to just reinforce the fact that I need to wait to plant seeds. I can always set up my grow lights and clear out some room to sort seed packets.

  3. Susan says:

    I am so bummed! Loved this podcast. I agree with others that it was perfect timing! But, what was not perfect about the timing was when I listened to the podcast. I just listened to it this morning and was excited to sign up for the master seed starting course. Unfortunately, registration was closed as of yesterday. Wondering when he will offer it again.

    1. margaret says:

      Hi, Susan. Registration will be open again Feb. 8 and 9 apparently, and a week after that again for a couple of days — I just inquired, so I would check back Saturday.

  4. Forrest Jones says:

    Margaret, you and Joe always make me smile and give me a chuckle when you get together. Plus I always learn something from your collaborations. But you did leave the cat out of the bag this time young lady. I know now that you have a master carpenter friend, Tom, who I am sure could rig up a “bear resistant” bird feeding contraption.
    Thanks for another great podcast.

    1. margaret says:

      The transcript here on the blog is the “notes” (I say that on the show so people listening would know to come to the website for more info, photos, links, etc.). What was the detail that you wanted to know more about?

      1. Deborah Hagy says:

        I only listened to the podcast. Now I see that your transcript has links to all the items he mentioned like the dual timers and t5 lights. Sorry I initially missed it.
        I have been starting plants indoors for 25 odd years with great success, yet I gained MUCH new information from this podcast. Thank you so much.

  5. Laurie says:

    Hi Margaret. Love your podcast and website. Is there a coupon available from you to sign up for Joe Lamp’l s course?? He opened it again … yay!!
    Thanks Laurie

  6. Matt says:

    Hi – I really enjoy this show! I have a comment / question about light position with T5 fluorescent tubes. In the conversation, you all were discussing how these should be further away from the seedlings than a regular fluorescent. I use a T5 and placed mine this year around 2 in. above and have in fact noticed that they have been growing very, very slowly. I do notice growth, and the leaves don’t look scorched, but they are not filling out like I would have expected. I’m at home all the time now and look at them more than usual, so maybe it’s just me being impatient, but do you think the light being too close may have stunted or slowed growth?

    Thanks, Matt

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