FOR THOSE PONDERING starting seed indoors, ever wonder what growing medium and other indoor propagating gear is best, from flats or pots to heat mats and lights? And what’s worth growing from seed, anyhow? Or: How can we water seedlings the best way and otherwise care for them expertly? Those are some of reader and listener questions my friend Ken Druse and I addressed.

It’s seed-catalog season, when we gardeners in many regions may not be able to grow much outdoors, but can dream big. Ken, author of “Making More Plants: The Science, Art, and Joy of Propagation,” joined me on the radio show and podcast to help us all get ready for a successful season of growing from seed.

This show and story is part of my annual Seed Series, and we’ll be giving away a copy of Ken’s book (see the comments box at the bottom of the page).

Read along as you listen to the Jan. 21, 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).

Q. We should tell everybody the backstory here. We solicited questions this year for the seed series, we solicited reader and listener questions over the holidays about growing from seed, and we want to thank them. We got like a bushel of them, didn’t we?

A. Oh, my gosh.

Q. We got so many good topics from everyone that we’re going to do two shows, this one this week, and one a couple of weeks hence, to, sort of, try to cover all the subjects. We’re going to give away a copy of-

A. Oh, of “Making More Plants?”

Q. Each time, yes. I love your book and I know it’s a wonderful book. I mean, it’s not just about growing from seed, it’s about propagating of all kinds, yes?

A. Yes.

Q. In this first show, maybe let’s talk about kind of getting ready. Let’s do them, sort of, chronologically, like the planning, the gear, the getting setup, once and for all correctly so that you can have success. Because a lot of the questions centered on that, not to my surprise, you know, because we all have issues with the technical.

what’s worth growing from seed?

Q. A great question from Madeline was, “O.K.,” she says, “what’s the biggest waste of my time to start as seed? I want to grow so much, but when should I just start with transplants?” That’s a really good strategic thing to think about first, isn’t it? [See the subheading below, “Direct Sow, or Start Indoors?” for more on that.]

A. Yes, and you’re making me think of exactly that problem. You look in the catalogs and you think, “Oh, that okra. That’s so pretty. Oh, look at that big, red, okra.” Then you grow okra and no one will eat it, so don’t grow something no one will eat.

Q. Right.

A. How’s that?

Q. No, I think that’s true, and similarly for me, there’s like a mathematics to it, an economics. I have raised beds, you know. I have X square feet in the sun of raised-bed space, and it takes this amount of time or that amount of time to grow a this or a that crop over how many square feet. Certain things cost $3 a pound or more, and certain things cost 79 cents a pound, and I can get them all the time. You know what I mean?

I want to grow what’s special, different, either a variety I can’t get anywhere, even if it’s of an everyday crop. Stuff like zucchini, am I going to give it 3 feet by 3 feet, you know, where I’m going to buy four zucchini from my farmer neighbor down the road, because he’s always got zucchini in the summer?

A. And he always needs to give it away. [Laughter.]

Q. I think there’s like a math to do, and I think it has to do with availability, and like you said, desirability, like do you want it? I mean, if you like cooking a certain cuisine, you need those herbs, right, if you can grow them.

A. Also, go to the farmer’s market and if there’s something that a local farmer is growing, and growing really well, maybe you want to support that local farmer and, you know, don’t grow that if it’s easier to get.

Q. Yes, five years, six years ago a number of young organic farm families moved to my town and one of them specializes in potatoes, and one of them grows a lot of tomatoes as part of their thing.

I rested my soil. It was great, because those things are related, and it is good to really rest your soil and not have those every year, you know, for pest and disease issues. I started buying big bags of potatoes and putting them in my fridge for the winter, and buying cases of tomatoes. They were organically grown in my neighborhood, like you said, and I’m supporting them. I think that’s right, too, is what’s available locally from people you wish to support especially.

A. Right.

oddball seed projects, including arisaema

Q. I asked people about what oddball seed projects they’ve tried, not that you and I have ever done anything crazy with seeds.

A. [Laughter.]

Q. I know you’ve tried some really nutty things, should I say that? Ha, ha, nutty things. Like what, Ken?

A. Well, once I soaked a coconut in the bathtub for six months.

Q. [Laughter.] That’s a big seed. What were you trying to do?

A. Well, coconut palms are really beautiful. Actually, now I see them from time to time. People get them at the flower market. They push up a stem and a leaf before they have a root, so I soaked this thing, and I soaked this thing, and it did split and something started, and then it died. So for six months, I had a coconut in my bathtub.

Q. That’s crazy. You have used your bathroom plumbing for other things if I remember correctly. What did you hang in your toilet tank? Didn’t do some crazy thing? [Laughter.]

A. Oh, you’re going to have me tell this? O.K.

Q. Well, you’ve told it to me before, so it’s a half memory.

A. I know, I know. O.K., so I really love, maybe it’s my, I shouldn’t say favorite. I really love odd jack-in-the pulpits and also the local jack-in-the-pulpits, so Arisaema, genus Arisaema. I remember when I started my garden, you could buy a tuber of a fancy Arisaema for, like, $30 for one tuber, but you could get seeds. You could get seeds from England, and you could get seeds from the exchanges, like the North American Rock Garden Society, where you give them seeds and then you get some seeds.

These seeds, ordinarily when they start on the ones that I grow myself, they form kind of a berry. It’s a long story, but if you take off the flesh from the berry then those seeds are going to sprout right away.

But when you get the dry seeds from an exchange, they don’t sprout. They’re cleaned of flesh and they’re dry, and so I tried and failed, and tried and failed, and tried and failed. And finally I asked someone who’s in the North American Rock Garden Society, “How do you start the Arisaema when they come dry?” He said, “Oh, it’s really easy. You have to rehydrate them. You put them in water for two weeks and you change the water six to eight times a day so they don’t rot.” [Above, Ken’s Arisaema seedlings at two stages of development.]

Q. Oh yes, I’ll get right on that. [Laughter.]

A. Well, he’s retired, you see?

Q. Yes.

A. I’m always cooking up something, so I put some of the dry seed in an organza bag and I hung it in the tank of the toilet.

Q. O.K., that’s what it was.

A. That’s important, not the bowl. In the tank with a paperclip.

Q. Right.

A. I just left them there for two weeks and the water gets freshened six to eight time a day. Then I took them out and sowed them and they all came up.

Q. Well O.K., so that would qualify as a nutty seed experiment.

A. You think?

Q. I mean, we had a couple of listeners who wrote in: Linda tried water chestnuts, not a giant success. Carol grew cardoons, which she really loved—beautiful and really successful, and she’s also had good success with growing artichokes in the mid-Atlantic region, she says.

A. Oooh.

Q. She took a crack at cardoons and she just loved it, a wonderful, ornamental and really loved it, as well as edible. That was kind of fun for her. Those are two that people shared with us, which made me think of wanting to hear your crazy ideas.

A. I think I’d do the water chestnut just like I did the Arisaema.

Q. Yes, similar.

A. I actually found water chestnuts on the banks of the Hudson River north of New York City.

Q. Oh, cool.

direct sow or start indoors?

Q. I suppose the first, sort of, overall question is what to start indoors and what to direct, and we’re going to do more on, sort of, the things that we sow outdoors in the second show in the seed series. Why do we start indoors? We start indoors because you and I are both in a cold zone, right, and we need a headstart especially on warm-season crops like a tomato, a pepper, an eggplant, whatever, basil. So we do it to get a headstart, right, I mean, generally?

A. With a lot of those plants, we don’t have a choice because they won’t take the cold. Any cold.

Q. And they need too long a time to grow up to maturity for us to direct sow them once it’s hot outside and warm enough outside.

A. Right.

Q. We do it for that reason. Then throughout the season, wherever you are, you may keep a supply of seedlings coming because sometimes the soil is too hot and dry outside to germinate any kinds of seeds, or especially certain cool-loving seeds. It’s easier to in a semi-shady place to grow more lettuce seedlings all season long or more kale seedlings all season long than to put seeds into hot, dry soil and have them dry up and die, you know, not germinate. That’s another reason.

• [My Seed Starting Calculator specifies which crops to direct sow, sow indoors, or which can be done either way.]

which germinating mix?

Q. A lot of the questions we go had to do with gearing up, you know, again no surprise, starting with the germinating mix.

Catherine wanted to know what the best seed-starting soil mix to buy was, and her complaint really was that the common one she’s used have, what she calls “rubble,” you know, large bits of bark or whatever, and she has to sift those through otherwise it, sort of, impedes smaller seeds. Other people chimed in and said what they’ve been using. Caroline wants to know what our recipes are, if we make our own medium.

Some people like KP asked about a particular one that Craig LeHoullier, the tomato expert friend of ours, and a lot of other people have recommended—the Johnny’s Selected Seeds 512 Mix—and why to use that. What do you use?

A. Well, you’ve made me think of, like, a million things, as usual. I think that the mix that you buy at the store with peat moss and perlite in it isn’t really so bad, and I’ve bought that, you know, years ago, and I’d add some coarse sand or some grit to that because it does pack down and kind of gets swampy unless you open it up. I haven’t found things to be too big.

For many years now, because I’m peat-free I could say, I’ve been using coir with perlite. You can now get coir that’s very finely chopped, but until very recently I would take coir and, maybe even compost, and rub it through some hardware cloth, like quarter-inch hardware cloth, which really makes it come out quite fine. You just rub it back and forth. I suppose you could do it if you had a very coarse sieve.

I make that fine, and then I’ll add some very coarse sand or some fine chicken grit to that just to open it up a little bit so it doesn’t pack down too much. If I’m using compost, or if I’m using coir that’s been around for a while, I sterilize my mix, and I guess that’s getting into the whole idea of cleanliness.

Q. Yes, which is key for seedlings to not transmit disease.

A. It is key.

Q. Right, because, like, John asked, he said, “Can I use…” you know, he wanted to know why fresh, clean potting mix is often recommended for starting seed, and when he has old soil from failed attempts, can he refresh it somehow? What you’re talking about usually, which is the heat method, to, sort of, pasteurize or sterilize it, it can be real stinky if you do it with old soil. Really stinky.

A. Or any soil. [Laughter.] It’ll fill the house. That’s what, usually, you’ll find recommended that people put it in a pan in the oven and you want to get it up to about 160 degrees, which kills most of the pathogens.

Q. Wow.

A. When I was writing “Making More Plants,” I started putting my mix in the plastic roasting bags that you can get for turkeys, or pot roast, or brisket, or something at the supermarket. I put it in the bag and leave plenty of space because it will have steam. I put in moistened, and I close the bag with the tie that comes with it, and I put it in the microwave on full power for about 10 minutes. I usually use an instant-read thermometer to see if I’m up to that temperature, but when I open the bag, you have to be really careful because it’s filled with steam-

Q. Steam, yes.

A. You could get burned. That’s what I do. I do sometimes reuse mix, but I sterilize it. Or, you know, as you said, pasteurize it.

Q. Really, don’t do this in the oven in the way that, you know, that’s going to stink up your whole house.

A. Well, you could do it with the bag in the oven.

Q. Yes, but what I meant was in, like, an open baking pan or something, that’s like a roasting pan. That’s not going to be a good thing.

A. Unless, you’re, you know, moving out for two weeks.

Q. [Laughter.] As far as the Johnny’s, that’s what I use is Johnny’s 512 and the reason being is that it’s got sphagnum, it’s got sedge peat mosses, you know, black peat mosses, it’s got compost, it’s got perlite. It does have some nutrients [like fish meal, but no chemical fertilizers].

A. Oh, oh my.

Q. It’s easier to wet it and it stays evenly moist, so it’s a good texture, you know, and it has good soil absorbency so it also good for soil blocking. We did have a question or two about soil blocking, making your own little, sort of … they’re not pots, but bricks of soil to sow into. Some mixes don’t hold together for soil blocking [above, a small blocking tool], so you’ve got to look on the bag if you want to soil block, whether it’s adapted to that. Johnny’s 512 is good for that.

A. You haven’t had any problems with it having nutrients in it?

Q. No, it doesn’t seem to be, like, you know, nuclear—like you-know-what brand and you-know-what brand from that chemical company.

A. The seed-starting mixes, if it’s commercial and you get it at the box stores, and it has any fertilizer in it, or has the name of fertilizer on the package, don’t do it.

Q. Yes, don’t do it. I agree because not all seeds need it, or want it, and it can be-

A. None of them need it in the beginning.

Q. It can be really bad for them, in fact, yes.

A. It burns them.

Q. Yes, or can just push them too fast, I think.

flats, pots, heat mats

Q. I wanted to compare, now that we have a medium—we’ve talked about your medium, what I use, what you use—I wanted to compare our gear, you know, what kind of pots, flats, cells, trays. What’s your general gear? Are you using cells or what are you sowing into generally?

A. Most generally, most of the things I do, I sow a lot of seeds in a 3-1/2-inch square plastic pot. I use square because you can get more of those in closer, you know-

Q. In a flat.

A. Closer together.

Q. Sure.

A. In a flat, right. If they’re round, they fall over, believe it or not. I use square pots, and I use 3-1/2-inch, and as I said, sow a whole lot of seeds, because I’m going to pot them on. I didn’t want to say prick them out. I don’t cut their heads off, which is what you sometimes do in the garden row if you’re direct sowing. But I do remove them once they have their first true leaves, which is the second set of leaves that resemble the leaves of the adult plant, and I move them to cells in a, I hate to say plastic, but what else is there?

Q. It’s plastic, yes, yes. I buy the heavier grade so that I’ve had some of them for five years. I don’t buy it every year, the junky stuff.

A. Good.

Q. Right. I sometimes sow in fiber pots, you know, like small fiber pots. They’re, kind of, a small rectangle. I don’t know if they’re 8 inches by 6 inches, or something like that. You’ve seen them. You’ve probably bought things at the garden center in them. I use these fiber pots because, like, sometimes I just want to do six or eight kale seedlings or something. I’m a small family and I don’t need a ton of something; I don’t need a whole big flat, but I want to do a lot of different things, like a couple of kinds of kale, and a couple kinds of lettuce, so it’s kind of like a mix-and-match modules. It’s, sort of, like a six-pack, but without the cells, and I can divide them up like you’re saying. I don’t have to move them as quickly as you have to out of your smaller pots, but I use those sometimes, too.

With stuff like onions, I use an open flat. I don’t put it in cells or small pots at all. I do it in an open flat. [How to grow onions and leeks from seed.]

A. I’ve made pots out of newspaper with the, I don’t know. Have you ever seen those mechanisms?

Q. Sure, it’s like a dowel. [The tool, above.]

A. Yes. Then you can, instead of a peat pot, which I hate, then you can take that, once you move them up, the seedlings, then you can plant that directly in the garden and that worked pretty well.

Q. Germinating mats, real important to say, I don’t know if you use them, I use them-

A. I do.

Q. Under a lot of things. The word, the name of it is the tip-off that I learned from a plant physiologist at Cornell who studies seedlings, vegetable seedlings particularly: germinating mat. It is not a growing mat, it is a germinating mat. The minute that the thing germinates, get that baby out of there. Young plants don’t want heat. Even the heat lovers don’t want their soil cooking. You know what I mean? 

A. Yes.

Q. It’s a germinating helper.

A. Well, they get too long and leggy.

Q. Exactly, and similarly get that hood, if you have plastic over your flats or one of those hoods, a clear plastic hood–that comes off, too, what would be called the germinating chamber in a laboratory. Both the bottom heat and the humidity dome, or film, have to come off as soon as your stuff germinates. Otherwise, it’s one of the big reasons for seed failure.

I wanted to get on to light, because a lot of questions spoke to that–and by the way, Jamie had talked about learning the hard way that lettuce hates warmth, in particular. A lot of people had mentioned the heat thing. Sherry talked about spindly seedlings and what to do about them, and would a fan help, and, etc. other people mentioned spindly seedlings in their questions. Light is super important, obviously, and windowsills are just, I think, a total no-no. Don’t you agree?

A. Yes. Well, I suppose if you a south window and you lived near the equator, or something. In general, you just can’t give them enough light-

Q. Right.

A. …on a windowsill.

Q. Right. All this stuff. I recently did an interview with Leslie Halleck, who wrote a new book about growing under lights in 2018, and it explains a lot about the details of this. Generally speaking, and LEDs are coming onto the market more and more, and they’re getting more affordable, but even the high output T-5 lights, or T-5 HO high output lights, the, sort of, thing fluorescent tubes in a mirrored hood, you know, a reflective hood on an adjustable frame, like the Jump Start, inexpensive Jump Start systems or the ones from Hydrofarm. Lots of easy ways to do it, but the T-5 high outputs are still a really choice. Much more light, but still not as much light as outdoors on a spring day. You know what I mean?

A. Right.

Q. I carry my guys outside, and I’ll give my light protocol. [My approach to light and why  I carry them outside on fair days is in this story, and summarized in the graphic above.]

A. You want to have the seedlings, like, two inches below the lights, which people can’t imagine. If you have a light unit and it has chains, you can raise and lower the light, but then when you have different flats or trays, and the plants are coming up but with a different speed, and how do you do that? I’ve been using plastic deli containers, the pints and the quarts. I’ll raise the flat, using those inverted containers so that the seedlings are raised up to the lights and if the ones haven’t come up yet, and they’re a little further away, then they can be a little further away because you can’t have everything at the right place at the right time unless you’re doing an entire four foot by two foot area with one kind of seed.

Q. Well, and that’s the other reason I like to use my fiber pots is because I can have, if one variety is up and running, I take it off the heat mat. You know what I mean?

A. Right, right.

Q. Similarly, with your little pots, you can do the same thing. When it’s up, take it off the heat mat. We only have a couple of minutes left in this segment, but I want to make sure we cover watering, at least, briefly. I loved my old APS system that used to be sold, sort of these foam compartments and then they stood on top. They had hollow bottoms and they stood on top of capillary felt mat that dipped into a reservoir and self-watered. They’re not made anymore, but there are things like Speedlings and Growease.

Watering: Are you a bottom waterer or what do you do?

A. I am.

Q. Tell us.

A. I water from the bottom. If the seedlings are up, and since I top-dressed, we didn’t talk about that, but-

Q. Well.

b. Since I top-dress with either chicken grit or very coarse horticultural sand, I can water from above, but I usually use, what we used to call, a bulb mister.

Q. Yes, I use it, too. Yes.

A. You can still find them and they’re not very expensive. My mother had one for ironing, you know, 40 years ago.

Q. I have a hand pump sprayer that is like 2 liters, and it gives you this similar kind of thing, and it’s controllable, and it’s small enough to spray.

A. It won’t dislodge the seedlings?

Q. No, at all.

A. Generally, I just put, especially when I start, I’ll sow the seeds and then I’ll place my 3-1/2-inch pot, or several of them, in a tray with about 3/4 of an inch of water. When the grit on the top turns from light to dark, I take them out. Takes about a half an hour.

Q. Quick as a bunny, tell us why you put that grit on the top as a mulch to prevent what?

A. Well, I started doing this about 15 years ago. I really do it with everything. I put this, kind of, top layer, just one or two thick of chicken grit, or coarse sand, and I haven’t had damping off, the dreaded fungal disease, that makes-

Q. That collapses them, yes.

A. The seedlings keel over, right?

Q. Yes.

A. I haven’t had that happen, knock on wood, once since I’ve been using this inert material on top. It doesn’t stay wet and it doesn’t encourage the growth of anything. It’s really just a miracle.

Q. It’s like having clean straw around your tomato plants in the summer. Those soil-born fungal spores can’t get up onto your plants. They can’t splash up. Same thing. It’s like a barrier.

A. Right.

Q. It’s a great idea. Ken, we have gotten our first seed series episode done, and we will be back with another in a couple of weeks. Thank you so much. I’ll talk to you soon.

enter to win ‘making more plants’

KEN DRUSE WILL BUY a copy of his book “Making More Plants: The Science, Art, and Joy of Propagation,” for one lucky reader. All you have to do to enter is answer this question in the comments box at the very bottom of the page:

What thing that you have started from seed is the wackiest ever (anyone but Ken ever grow a coconut?), or if not wacky, what do you most love starting seeds of? (I would never garden a year without pole beans, as easy as they are, and the first time I succeeded with onions was a real thrill.)

No answer, or feeling shy? Just say “count me in” or something to that effect, and I will, but an answer is even better. I’ll draw a random winner after entries close at midnight Tuesday, January 29, 2018. Good luck to all; US and Canada only.

more on seeds

• The Seed Starting Calculator (when to start what)
• How I pick what seed catalogs to shop from
• The Seed Series: expert interviews
• All my seed-starting gear

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 Jan. 21, 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).