This basic setup seemed to do a reasonably good job of getting the seeds seemed, but the seedlings didn't really thrive. Even after weeks under the lights, they were always much smaller and scrawnier than the ones sold at the annual Rutgers plant sales. I mentioned this problem to the landscaper we consulted with in 2012, and she explained that the seed-starting mix is a good medium for starting seeds, but not for growing plants; it doesn't provide the nutrients they need. She recommended starting them in this mixture and then, once they'd sprouted, transferring them to larger containers of real garden soil. But this idea posed several problems:
- It wouldn't allow us to use our handy seed-starting tubes. We'd have to start the seeds in small containers and then transfer them to larger ones, which might not fit in our juice-box trays, which in turn might mean that we wouldn't have room for all our seedlings in our DIY lighted tray.
- It would be a lot more work, because we'd have to plant each seedling twice—first planting the seed in the starter mix, then transplanting the sprout to real soil—before it could even go out into the garden.
- It would pose a greater risk of "transplant shock" to the seedlings, because each one would have to be uprooted and replanted twice (starter to soil-filled pot and soil-filled pot to garden).
So I started doing a little research on the subject. I found that different sources actually recommend quite a variety of methods for starting seeds:
- The most common advice is to start the seeds in a sterile, soil-free starter mix, then transplant them to soil, as recommended in this article from the Old Farmer's Almanac. But this is the method we rejected last year because of the hassle and the doubled risk of transplant shock.
- Many other sources, such as Organic Gardening, recommend avoiding this problem by start the seeds in a sterile seed-starting mix and just keeping them there, adding fertilizer to them to provide the nutrition they need until it's time to plant them. This is less risky than the first method, and it's not as much work, but it doesn't seem very ecofrugal to buy a synthetic fertilizer if your plants could get all the nutrients they need from free garden soil.
- Burpee claims you can just leave your seeds in the starting mix with no fertilizer at all, since "seeds contain the nutrients the seedlings will need." But this is the method we were using up until 2012, and the resulting seedlings were pitiful.
- A WikiHow article suggests tackling the problem from the other direction. Instead of starting the seeds in a starter mix and adding fertilizer, it recommends sprouting the seeds with no soil at all, just a damp cloth, and then planting the sprouts directly in garden soil. It's an intriguing idea, but I'm not that confident about it. A lot of other sources suggest that baby seedlings really need a loose mix that holds in moisture well, and most recommend that it also be sterile to protect the seeds from germs. I don't know how well such tiny transplants would fare well in straight-up garden soil.
- An old article from Mother Earth News recommends making your own light-yet-nutritious potting mix by blending compost with peat moss or coir. The article says to sterilize the compost first to make sure it's pathogen-free, and cover the newly planted seedlings with vermiculite to hold in moisture. This sounded more promising, but it seemed like a lot of work—first sterilizing the compost, then mixing in the peat—and it would require buying some pricey and non-renewable ingredients.
- Finally, after digging through the first page of results, I managed to find one source that recommended a variant of the layering technique Brian had in mind. This paper from the Department of Horticulture at Purdue said one good method for starting seeds was to "partially fill a flat or pot with sterilized soil mix, and then top it with a layer of vermiculite or milled sphagnum moss in which the seeds are planted." It also said you could just use "a mixture of about one-third loam garden soil and two-thirds vermiculite," provided the soil was sterilized.
So basically, it looked like the key to growing our seeds in ordinary soil was going to be sterilizing the soil first. That would protect the seedlings from germs, but still give them the nutrients they need as they grow. The Purdue paper helpfully outlined a method for sterilizing ordinary garden soil: put it in a baking dish, cover it with foil, and bake it in the oven at 200 until the temperature of the soil reaches 160 to 180 degrees. Or, if you don't have a candy thermometer, you can "place a raw potato in the center of the soil and bake in a medium oven until the potato is done."
So on Saturday, Brian went out to dig up a bit of soil from one of the garden beds. Both a trowel and our King of Spades bounced right off the frozen ground, but our Structron Super Shovel, with its vicious pointed teeth, bit right into it and tore up a nice big clump, which Brian then managed to get spread out in a baking dish. The Purdue paper warned that it would "give off a strong odor" while it was baking, and it did—a very unpleasant, acrid odor, heavy on the ammonia. So Brian kept the range hood running for about an hour after removing the pan, and he transferred the pan itself down to the basement to cool down. I peeled back the foil just long enough to get a picture, but the whiff I got while the foil was off was enough to convince me to put it back in place and leave it well alone.
Next, he lined up the tubes in the carton. Since we only need about four parsley plants, if even that many, he prepped just six tubes, filling them about 2/3 full with the sterilized soil...
...and then topping them off with bagged seed-starting mix.
He tucked the little seeds into this top layer, misted them well with water, and covered them with a panel of clear plastic to help hold the moisture in.
They're sitting now on our designated seed-starting table in the guest room, where they will be joined in about two weeks by leeks and broccolini, then marigolds, tomatoes, and Brussels sprouts a month after that. There may be ice on the ground and snow on the way, but the 2015 garden season is afoot!