We’re finally to the approach I use the most: starting seeds in plastic pots. (If you’re considering using some other sort of container, check out Alternatives to Sowing in Pots.) I respect the concern about using a lot of plastic in the gardening process, but in this case, it’s mostly a matter of reusing what’s already on hand from previous plant purchases. Most plastic pots can be reused for several years; in fact, my favorite seed-sowing pots are decades old now, leftover from when I had a nursery 30 years ago.
One thing you may notice in the photos here: I do not clean (or sterilize) my pots before reusing them. Should you? Probably. It can’t hurt, anyway, if you have the time and inclination. I used to, when I was newer to the seed-growing game, but I have to admit that I haven’t for twenty-plus years now. My pots may have some old growing medium clinging to the inside, or mud on the outside from planting-out sessions, but I haven’t found that to be a problem. If I knew I had issues with fungal diseases, like damping off, then I would be more careful, but that’s rarely a problem for me, thank goodness. I leave it to you to decide what works best in your situation. If you are having trouble with your seeds not germinating, or if they keel over soon after sprouting—which can indicate damping-off—I definitely recommend starting with clean pots (and fresh seed-starting medium too).
Deciding on a Size
When you start saving pots to reuse, you’ll very likely end up with a variety of sizes to choose from.
I can’t remember how I ended up with these 2-inch square pots, but I really like them for starting small seeds. They are well balanced and hold a reasonable amount of growing medium, and I can fit 21 of them in a standard-size flat (tray), which means I can start many kinds of seeds in a small amount of space. The rooting space is rather limited, though, so I try to move seedlings out of them as soon as possible.
These 3-inch pots are from previous herb purchases, I think. They too are handy for starting small seeds, but as they are somewhat taller, they’re a little less stable if they’re not in a tray.
I have loads of these 3.5-inch pots: some leftover from my nursery and many from plant purchases over the years. They work well for a wide range of seed sizes, are stable enough to not tip over too easily, and hold enough growing medium that the seedlings can stay in there for a few weeks, if needed. You can fit 18 of these into a standard-size flat.
I don’t use my 4-inch pots too often for sowing, except maybe for large seeds, because they take up a lot of space under lights. I mostly save these for potting up seedlings.
If I had to start over with just one set of pots, I’d probably stick with the 3.5-inch ones, as they work well for both seed-sowing and seedlings.
Square versus round pots is pretty much just a matter of preference; the seeds don’t care. I’ve always liked square pots because they fit together so neatly, but you can use round ones if you have them.
There are many other kinds of containers you can use for starting seeds: Some are good and others can be problematic, in my experience. I cover my opinions in Alternatives to Sowing in Pots.
Filling the Pots
Regardless of the medium I’m using, I always moisten it first. Once it’s in a pot, it can be hard to get it evenly wet. I scoop some into a large bowl, guesstimate the amount of water to add, and then stir it with a trowel or my hands to get it evenly moist but not soggy. I like the medium to just hold together when I squeeze it lightly. If it’s too wet, I add more dry medium; if it’s too dry, I add more water.
I like to fill all of the pots I plan to use in a given sowing session at one time, filling each one nearly to the rim with the moistened medium and placing it in a plastic nursery flat.
If the seed pots will be staying indoors, I use a flat that doesn’t have drainage holes to minimize mess with later watering. If the seeds will be going outside, I make sure the flat does have holes in the bottom, so the pots don’t end up sitting in water.
It’s finally time to plant! I usually sow one or two flats of seed pots in one session, and to streamline the process, I stick the labels in the pots first and set each seed packet with the corresponding label. Sometimes I put the labels in alphabetical order and sometimes randomly. If I’m sowing several strains of one thing (three or four colors of zinnias, for instance), I make sure those pots aren’t right next to each other so the seeds don’t accidentally drift into the wrong pot.
By the way…one lesson I have learned the hard way (and continue to re-learn when I try to take the risk): Do NOT mix different kinds of seeds in one pot, flat/tray, or other sowing container. It may seem like a good idea for saving space, but you’ll find out otherwise when some of the seeds are grown and ready to be transplanted while others are not yet sprouted, and you have to try to get the seedlings out while not disturbing the seeds that are still germinating. And then you are stuck with a full tray taking up space while only part of it holds slower-spouting seeds. Having lots of seeds in one flat is also a problem if you end up with a disease problem, like damping-off, which can quickly kill off all of the seedlings. If you use pots, there’s much less chance of the disease spreading so fast. I can already hear some of you saying that you sow in open flats all the time and it works well for you. If that’s the case, great; keep doing it. But I don’t recommend it you don’t already have a good bit of seed-starting experience.
When I open each seed packet, I try to remember to do it over my bench, not over the prepared pots, for the same reason. Sometimes it can be hard to tell where the seeds are in the packet, or if they are loose or enclosed in another packet inside a larger one. I usually use scissors to make a clean, straight cut along the top edge of the packet, then pinch one of the cut sides to create a sort of spout that makes it easier to direct the seeds.
If you have a seed packet with a flap and prefer to pry it open, keep in mind that any exposed tape or adhesive will catch the seeds as they roll out and make sowing difficult. You can sow the seeds from the un-flapped side, but the flap may block your view if you don’t fold it back first.
Having handled many thousands of seed packets in my time, I have come to prefer sowing seeds from paper or glassine packets. These materials allow the seeds to roll out easily but usually provide just enough friction to keep them from all dropping out at once. And with the glassine, you can easily see where the seeds are and how many are left.
I have come to seriously dislike getting seeds packaged in resealable plastic packets. They are convenient for seed-sellers but can be hard to open for sowing, and then the seeds often cling to the sides, so you have to cut the seams to completely open the packets and pick the seeds off individually with tweezers. Argh!
Working with large and medium-sized seeds is simple: I pick them up with my fingers and place them on the moistened growing medium.
I sometimes sow smaller seeds directly from an opened packet by holding it almost horizontally and tapping it with a finger to get the seeds to come out one at a time.
When I am working with tiny seeds, or a very small number of seeds, I prefer to first roll them out onto a creased business card or index card and then tap them off of there. That way, I have an even better visual of the quantity left and can place them with great care. Spacing the seeds out as evenly as possible makes separating the seedlings later on a much easier job. (You may even want to sow one kind of seed over several pots instead of just one, for the same reason.)
It takes a bit of experience to predict how many plants you are likely to end up with, but don’t feel like you need to sow all of the seeds in a given packet. Sowing only part of them will give you a backup in case something goes wrong and you need to sow again.
Once I have all the seeds sown, I sprinkle moistened growing medium over the seeds that need to be covered. I have to admit to guessing at that most of the time. I generally add just enough to cover the seeds, unless they are very small; then I leave them uncovered. If I’m having trouble getting a particular kind of seed to germinate, then I will research to see if the sowing depth makes a difference and treat it accordingly.
After that, I use the backs of my fingers to gently press down the surface of each sown pot, to make sure there is good contact between the seeds and the moistened medium. This is an important step: If you leave it fluffy, the seeds will have a harder time absorbing the water needed to initiate sprouting, and they may dry out before they can sprout. Sometimes a seed or two from one pot will stick to my fingers and get transferred to another pot, but that’s easy to spot when one pot has a bunch of seedlings and a neighboring pot has a similar-looking interloper.
I sometimes follow the firming step with one more covering layer. On pots that will sit outside for the winter, I like to use a thin layer of some sort of sand or grit, like paver base or small aquarium gravel or a commercial product like Perma-Till (shown above and below).
The covering serves the same purpose as a mulch in the garden, protecting the seeds and keeping them from drying out. It may seem harsh to cover small seeds with stones, but if you’ve ever noticed how readily seedlings come up up gravel paths, you’ll know they can do just fine!
Last year, I tried something different: rice hulls. They are lightweight (obviously much lighter than gravel) and supposedly discourage fungus gnats: tiny insects that can produce root-damaging larvae. I didn’t notice much difference in that area, though, perhaps because I didn’t apply them thickly enough. They did tend to blow off the seed pots outdoors, and also ended up producing some rice seedlings in a few of the pots, so I probably will not try them again.
Once I am finished with the sowing, I water the pots. I used to do bottom-watering: setting the pots in a tray of water and letting them soak up the moisture until the surface of the growing medium looked wet. Eventually, though, I felt that made the growing medium too saturated, so I now just gently dribble water over the pots from a small bottle (like a plastic water or soda bottle). That thoroughly wets the surface, where the seeds are, and also helps to settle the seeds into the growing medium, but it doesn’t make the growing medium too soggy.
I also like to cover indoor seed flats with a clear plastic dome, or enclose individual pots in a clear plastic bag, to keep the humidity high close to the seeds while they are germinating.
All that done, it’s time to put the seeds in the right conditions for sprouting.