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Starting plants from seed

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Every gardener has his or her own preferred method of seed-starting. A lot depends on your favorite things to grow from seed: if you like lettuce, you'll mostly direct-sow in the garden; if tomatoes are your thing, chances are you start indoors in potting soil with bottom heat; and if you prefer finnicky alpines, you may engage in scatter-sowing across a grit-covered pot.

As much seed-starting as I do, I've tried most methods by now. I've hit on a favorite one that works for most varieties, but at the same time I've come to realize that different types of plants and seeds require different approaches. On this page, I'll try to sort through my rationale for deciding what method to use with which varieties. First, a summary of the methods I routinely use:

  • the baggy method, with all its variations
  • sowing to a cellpack - with and without bottom heat
  • sowing to a pot - inside, outside, or combinations thereof
  • direct-sowing in the garden

When I first started on my germination adventures, I went about it in a fairly traditional way: cellpacks filled with a seed-starting soil mix, a few seeds to each cell, each cellpack under the growlights. And that worked out okay. Sure, some varieties never germinated, so that their cellpacks sat uselessly under the lights, while others germinated like gangbusters, with multiple seedlings per cell. I usually didn't have the heart to snip extras, leading to delicate transplant attempts, but I had plenty of room and plenty of time - after all, I was starting just a few dozen varieties.

Then I started to get more and more hooked, and obtained hundreds of varieties from catalog orders, trades, and society exchanges. Now both space and time became more precious, and I adjusted my methods accordingly. Mostly, I gravitated toward my own version of the baggy method (also known as the filter paper method, or the Deno method). I describe the ins and outs of this method on its own page, but in short, it involves germinating seeds outside of soil, and transplanting them to containers to grow on after they germinate. Here are some of the advantages I see to this approach:

  • Seed varieties don't consume any cellpacks, soil, or space under the lights until they actually germinate. If they never germinate, they just get thrown out
  • It's much easier to subject the seeds to the cold and warm stratification treatments they need for germinating. Early on, I'd put entire cellpacks in plastic bags and set them in the fridge for their cold treatment. Three kids later, the fridge has no room for such frills, but all my baggies fit in a single tupperware container.
  • If you like to keep records and statistics of germination rates and yields, the baggy method can't be beat. You can see germination occur at its first stage, when a single small root emerges from the seed, and can keep records of how many seeds germinate, and how long it takes, in as much detail as you like. That's where I get the detailed information I present on my plant portrait pages.
  • Some varieties just germinate better given the baggy conditions. I don't claim to know why, but this has been my experience for several species.
  • Finally, some esoteric germination enhancement methods, such as treatment with Gibberellic acid, are ideally suited to the baggy method, which provides about as controlled of an environment as is possible.

Of course, there are disadvantages as well:

  • It's more work, in many cases. After the seeds germinate, you have to carefully transplant them to cellpacks or pots. If you'd have sown directly to soil, you could have saved yourself a step.
  • You have to stay on the ball - most varieties have a limited length of time after germination before they start really resenting growing in a baggy. Checking the baggies for germination every three or four days is a must.
  • Even so, some varieties just don't like the experience, period. For example, I've found that various penstemon species are much more prone to damping off or otherwise failing if they germinated in a baggy, instead of directly in soil.
  • Those really tiny seeds! Transplanting them after they germinate requires keen eyesight and a surgeon's steady hand, and many are easily damaged in the process.
  • Those really large seeds! They tend to make poor contact with the filter medium in the baggy, leading to delayed germination or root stress after germination. Anything bigger than a pea tends to be problematic. Even so, a baggy may still work - just use milled peat moss or potting soil instead of the filter.
  • Giving more than one warm-cold cycle gets to be tedious in baggies. And providing the fluctuating temperatures that some seeds need to germinate (examples: Bells of Ireland, cleome) is nigh impossible in the baggy environment. In both situations, Mother Nature does it better

So from a good number of years' experience, I've come up with a few heuristics for germination method selection:

  • Seeds for species that are new to me, especially perennials with uncertain germination requirements, I almost always start in baggies. That way, I have complete control, and can keep the most accurate records, which will help me decide how to proceed in future years.
  • An exception to that is when I know (from germination databases, internet search, or trading partner advice) that the seed needs an extended cold stage, perhaps more than one cold stage, or fluctuating temperatures. In those cases, I tend to sow directly to a 3½ inch pot, which I bottom-water thoroughly, and cover with grit to help keep moisture in and algae/moss out. If my sources suggest that an initial warm stage is helpful, I keep the pot inside for the suggested amount of time, otherwise, out it goes, for a winter's worth of natural conditioning. Come spring, I check the pots regularly, make note of any germination, and plant seedlings out when they're large enough to handle. Some pots stay in my outside germination area for several years before I give up on them.
  • Tiny seeds that are painfully difficult to handle, I usually sow directly to the top of a 3½ inch pot with potting soil, water in thoroughly, and set under my growlights for germination. Seeds that dislike baggy germination or that seem to do better direct-sown (penstemon, hosta) also get sown directly to pots. Since these tend to have unpredictable germination success rates, I prefer pots over cellpacks. If after a while a pot gets too crowded, I'll transplant to cellpacks or individual small pots.
  • For annuals and vegetables that germinate easily and in great numbers, I often bypass the baggy hassle and resort to the ol' stick 'm in six-pack method. I double up on the seed, use exactly as many cells as the number of plants I want, and ruthlessly lop extras. It's quicker, and many of the baggy method's advantages don't really apply.
  • Finally, there's sowing in situ outside. I use this for plants whose seedlings really dislike any kind of handling (poppies, mainly), and some other perennial and biennial plants known for self-sowing (e.g., foxgloves). There's a lot more room outside, so you can get a larger crop of plants; they'll stay small their first year (no head-start on the season), but if they're not going to flower anyway (most perennials and biennials won't), then it doesn't really matter.

What shall we feed them?

Luckily, deciding what to feed my seedlings is infinitely easier than figuring out what to feed the kids! The seedlings are not nearly as picky. As a matter of fact, I don't really feed them anything as long as they are in small cellpacks, and they do just fine. When they get a little bigger, and get transplanted to their own pots or deep six-packs, I water them in with some dilute fertilizer, and from then on they get a regular diet of weak nutrient soup. Until last year, I used Neptune's Harvest and was happy with it - but no matter how much they try to tell you this stuff has no smell, they are lying! It stinks! So when my wife needed to store food items in the same half of the basement, the situation became untenable, and I switched to small doses of all-purpose chemical fertilizer. If you do use fish fertilizer (it's supposed to have nutrients and stimulants that synthetic fertilizers can't provide) just remember to water in such a way that any liquid is rapidly absorbed into the potting soil (either by bottom-watering or top-watering), and the smell doesn't linger. Do not, however, make up a batch of the diluted stuff and let it sit around: the stench has a way of permeating things. I didn't really mind it - it just went along with one of my favorite activities. Whichever fertilizer you use, be sure to dilute it down to 1/4 or 1/2 the recommended strength.

How long to keep seeds

Most people underestimate how long seed stays viable. Certainly, the best-by date varies with the plant species, and some won't even last a few months in dry storage. But most keep for much, much longer (for example, big bluestem grass). Some, like peppers and tomatoes, slowly lose viability, so that you need to plant more for a good crop. Others seem to just never give up. In the seed-starting details (see below), I try to indicate the age and origin of the seed, so that you can judge whether they deteriorate with time.

Most seeds remain viable longest when stored cold. I have more seeds than would fit in the family fridge, so I keep them in a box in our basement, where the temperature fluctuates from about 60°F in winter to about 68°F in summer. This seems to be fine for most seeds. I make an exception for a few notoriously short-viable seeds, which I stick in a corner of the fridge (in the same tupperware container as my cold-stratifying baggies).

Is this real seed?

When you buy seed from commercial sources, you can pretty much be sure that the little things inside are indeed seed (you can't always be sure they are viable, especially if they've been sitting around in a department store for months). But when you trade for seed, you can't always be sure. I've gotten many packets full of fluffy chaff through the years.

Especially prone to seedlessness are trades of hosta, gerbera, clematis, pulsatilla and ligularia. For all of these, the seeds should be fat and solid - they are easy to distinguish from chaff, which is just fluffy stuff, sometimes with flat empty husks. If you can push down on seed without feeling resistance, it's probably not viable. Smaller seed is harder to judge - sowing thickly is sometimes the only way to make sure that you're sowing some seed along with the chaff.

All of these are just my personal observations. Please let me know if your experience is different.

You may also be interested in my list of perennials that bloom in their first year from seed.

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Last modified: February 12, 2011
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