I’ve gotten quite a few emails asking about seed-starting in the last few months, mostly from those of you who took part in my seed giveaway last fall. The same thing happened last year, so I should have known to give specific sowing directions along with the descriptions. I guess it’s just that my usual approach to starting seeds these days is about as low-key and low-tech as you can get, so I normally don’t think much about the details. See, my fantasy seed-starting setup would look something like this:
The reality looks like this:
Yeah, just a couple of 4-foot shop lights with ordinary fluorescent bulbs and a heating mat on a portable rack right here in my office. So even though I sow well over 100 kinds of seed every year, I have to keep it simple. Only those that really need an early start and/or warm temperatures (coleus, basil, alternanthera, cotton, tomatoes, and so on) get the full lights-and-heat pampering, and they have to be spread out into early March, late March, mid-April, and early May sowings.
Indoor-sown seedlings of Alternanthera dentata ‘Purple Knight’
Once they’re up, most have to deal with the seedling shuffle: out on the porch or into the unheated greenhouse during the day and back into the house at night. It’s not optimal, but it works.
Anything that can possibly wait for outdoor sowing, either in pots or right in the garden, does wait.
And anything that I know will self-sow has my blessing to do just that (well, within reason).
Self-sown Atriplex hortensis ‘Rubra’ seedling [March 21, 2012]
If I need to deliberately start more of a self-sower, or if I have new seeds that need or tolerate a chilling period, I’ll sow them in pots in winter—usually in either Fafard Growing Mix or Pro-Mix BX. (I use the same mix for all seed-starting, growing, and container plantings.) Then I top the pots with a quarter-inch or so of grit: either Turface or Profile Soil Conditioner (shown below) or fine aquarium gravel. The grit isn’t absolutely necessary, but I think it helps to keep the growing mix from crusting over when it dries out.
The sown pots then get settled into some vacant space in one of my holding beds…
…or put into a cold frame, or set out on the porch steps, and left there to sprout whenever they’re ready to in spring.
Angelica archangelica ‘Corinne Tremaine’ sown in early January and placed outside; germinated in early April
I wasn’t always such a casual seed-starter, though. Back in the late 80s, when I was still a geek-in-training, I was obsessed with starting any seeds I could get my hands on. Back then, of course, you couldn’t simply go online and order anything you wanted. I joined a bunch of national and international seed exchanges, and even subscribed to a few plant expeditions, and ended up with all kinds of rare and unusual seeds. That was all great, except for the fact that I lived in an apartment at the time, which rather cramped my seed-sowing capabilities. The solution to that came along in 1991, with the arrival of Dr. Norman Deno’s amazing book Seed Germination Theory and Practice.
It sure didn’t look like much, with no attention to design and little if any editing, and reproduced at a copy center. At the time, I was used to working on highly polished and highly visual gardening books at Rodale, so I couldn’t help but be underwhelmed when I first saw the plain paper cover, but what I found inside absolutely blew me away.
Dr. Deno was a chemistry professor at Pennsylvania State University who developed an interest in seed germination from a scientific standpoint. He designed an approach to studying germination that was both incredibly simple and exquisitely detailed. The few materials he used for his experiments are common household items, but he applied his extensive scientific knowledge of chemical processes and drew fascinating conclusions from what he observed.
I wish I could go into more detail about some of the results I found most interesting, but you’d still be reading this post tomorrow if I did that. The key principle, though, is that all species have some way of delaying germination so their seeds have a chance to get dispersed before they sprout. Otherwise, the seeds would start growing right on the plant they form on, or around the base of that plant, and the species would not have a chance to move into new territory. In some cases, it’s a physical structure (such as a very hard covering) that keeps the seed from sprouting right away. Most often, though, it’s some sort of chemical delay mechanism, such as a necessary drying period. Some other factors that can help to destroy germination inhibitors include exposure to moisture, certain temperatures (warm, cold, or oscillating), light, and time.
Dr. Deno’s goal, as summarized on the cover of the second edition of his book, was “the discovery and description of such mechanisms and the development of procedures for removing them so that the seeds can germinate.” By the time he published the first printing of the second edition of his work in June of 1993, he had concluded experiments on 145 families, 805 genera, and approximately 4000 species. The two self-published editions, as well as two supplements containing his later findings, weren’t ever widely distributed beyond the world of fanatical seed-starters. But bless him, he made them available in 2010 for free public access through the USDA National Agriculture Library, so now we all have access to most of them at the links below. (Be aware that these are large files.)
- Seed Germination Theory and Practice, Second Edition (pdf)
- SGT&P First Supplement (pdf)
- SGT&P Second Supplement (pdf)
Dr. Deno did not prepare an index for his germination-related works, which made it a bit challenging to find all references to species of interest in the print versions. When you access the pdf files, though, you can use the search function to hunt for the details you want. Or, you could try this index:
Dr. Deno wanted his work to be useful to growers and gardeners, so he wrote up his results for a general audience, not as scientific papers. It’s far from light bedtime reading—some of the concepts and explanations take a good bit of concentration to absorb—but you don’t need a degree in chemistry to understand and apply his process and results. I highly recommend reading the first 20 pages of the book to start with, just to get a feel for what it’s all about, then dipping into the other chapters once you’ve had time to absorb the basic concepts.
As I mentioned before, you can find everything you need to try his basic techniques around your house or in one trip to a grocery store: a roll of good paper towels; a box of cheap, thin-plastic bags (either sandwich or 1-gallon size, not the resealing kind); and a thin-point permanent marker.
Now, you may be thinking that germinating seeds in paper towels is hardly ground-breaking (so to speak), and you’d be right. You’ve probably run across the idea as a project for kids, or as a technique for testing the percentage of seed germination, as explained on sites like this one: Seed Germination. And really, even Dr. Deno wasn’t much for using the paper-towel technique for routinely sprouting all seeds for the purpose of producing plants. In some cases, he recommended sowing directly in the ground, or, for many species, in pots with an approach he called “bagging”: filling plastic pots with growing medium, pouring boiling water over the surface three times, surface-sowing the seeds, enclosing the pots in the thin plastic bags, and then setting them under fluorescent lights.
I do prefer the paper-towel technique for starting some seeds, though, and I’m looking forward to using it again this year, for several reasons.
First, it’s terrific for seeds that take a long time to germinate. Instead of having to use up growing mix, pots, and space and then wait several weeks or even months to see if the seeds are going to sprout, you can sow them in the amount of space an index card would occupy, keep them in the ideal temperature and moisture conditions, and not worry about pests or diseases bothering them. It’s also easy to tell if the seeds aren’t viable, because they’ll start rotting in the first month or so, and you can just throw them out instead of continuing to water and wonder when or if the seedlings will appear.
Dry-stored Cyclamen hederifolium seed sown August 10; germinated early October
As Dr. Deno’s work shows, the seeds of some species need “conditioning” periods at alternating temperatures. In his experiments, he used 40°F (4°C) and 70°F (21°C) for the sake of convenience: 40°F being the average setting of a home refrigerator and 70°F being the usual home room temperature. We’re used to sowing seeds and keeping them warm until they sprout, but some seeds need some time at 40°F before they sprout at 70°F. (Dr. Deno usually used 3-month periods in his experiments, to correspond with the seasons.) Other seeds need a period at 70 and then sprout at 40. And still others, such as a number of species in Liliaceae and Ranunculaceae, need multiple cycles of warm and cold temperatures.
When you sow these “multicycle germinators” in paper towels, it’s very easy to keep track of the timing of the cycles and to provide the appropriate temperature no matter what the weather. And while you’re waiting, you know that the seeds are safe from being munched on by mice or other critters.
The paper-towel method is also very handy if you’re working with chaffy seeds. When you get seeds from seed companies, they’re usually well cleaned. Seeds from friends or seed exchanges, however, may still have a fair bit of debris mixed in, sometimes to the point where you’re not sure what is seed and what is chaff. When you sow on paper towels, you’ll notice fungal activity on the bits of chaff within a few weeks. It can be a little alarming to see that, but these fungi are interested in breaking down dead stuff only, so they don’t bother live seeds and won’t interfere with germination. I like to pick off the seeds and move them to a fresh paper towel, though, because the original one can get a little whiffy.
Sowing on paper towels is a great way to learn how to identify seeds. When you know what they are and see them frequently while you’re waiting for them to sprout, you eventually build up a good mental archive what they look like, making it easier to recognize unlabeled seeds in the future. That knowledge also makes you much better at gathering and cleaning seeds, because you’ll know what you’re looking for when you’re collecting and what the end product should look like when you’re separating the seeds from the chaff.
If you’ve been given unidentified seeds and have little or no idea of what they are, the paper-towel method lets you easily experiment with various temperatures and light conditions to see if you can get them to sprout: the first step to growing and then identifying them. Observing how the seeds germinate, what conditions they germinate in, and how long it takes them can also give you clues to their identity.
I like this approach for very special seeds, too. Several of you have shared some real treasures with me this winter, and I want to give them the best possible conditions to get them started. And when you get just two or three seeds in a packet, when you’re dealing with something quite rare, or when you’ve spent a good bit of money or effort to get out-of-the-ordinary seeds, it just makes sense to keep a close eye on them.
Do I need to say that this approach is also a lot of fun? You can easily sow dozens of kinds of seeds at one time right on your kitchen counter, without having to deal with growing mix or watering or trying to find room for all the pots. You get the excitement of opening the towels often to see if anything is happening, and the thrill of seeing germination happening right in your hand.
Success! Seeds of ‘Gat’s Variegated’ rhubarb sprouted in 4 days at 70°F
With seeds that usually sprout at 70°F, I leave them alone for the first 2 or 3 days, then open their towels once a day for the next week or two. There’s usually a lot of action during this period. After that, I check the remaining seeds every 3 or 4 days for a few more weeks, then once every 7 to 10 days until they sprout. Seeds that need one or more 40-70 or 70-40 cycles won’t appear to be active during their first temperature period, at least, so you’ll check on them only every few weeks to make sure they are still alive and that the towel they’re in is still moist. You’ll want check on them more frequently soon after you move them to a new temperature.
When you see the first sign of sprouting, pick the seeds off the towel with tweezers and place them in a pot of growing medium: right away, if possible, or at least within a day or two. If you wait too long, the roots grow into the paper, and it can require some patience to peel away the towel and get them out without damaging them.
This isn’t a technique that works well for all seeds and all situations. I wouldn’t recommend it for tiny seeds, for instance, because they’ll probably root into the paper towel before they’re large enough for you to move them to a pot. It can also be a problem if you don’t have time to check the seeds regularly and plant them before their roots get seriously tangled into the towels. And with really easy germinators, like most common annuals and veggies, sowing into pots or directly into the garden is simply more efficient.
If you want to work with some less common species, though, or if you’re interested in learning about the science and observing the magic of germinating seeds up close, I encourage you to download the Deno book and supplements, grab some paper towels and plastic bags, and give this technique a try for yourself. I’ll be very interested to hear what you think of it.