Gardening takes karma very seriously.
Last year, I was bragging about my incredible tomato-growing skills. This year in mid-January I started pre-sprouting tomato seeds and by March very few of those 30+ varieties ever made it to a pot. By very few, I mean about five out of every hundred seeds.
So what happened? Besides, of course, an overdue lesson in humility?
There could be lots of reasons a tomato seed doesn't sprout as planned. In the past I've always blamed the seeds. This year, for lots of reasons, that probably wasn't the case.
The Seed Pre-sprouting Method
I've had a lot of success spouting and starting tomato seeds early, so in late January I plugged in the heating mat (about $30 online) and put tomato seeds in wet napkins in labeled sandwich bags.
This is the pre-sprouting method my friend Jay Tracy, an incredible gardener and cucumber melon expert, recommended a couple years ago. By this method, it's possible to speed up the germination process by days and even weeks compared to planting a seed directly in a pot or the ground.
The setup is pretty simple. You need paper napkins or paper towels, plastic sandwich bags and, ideally, a heating mat. Wet the paper napkin evenly and squeeze the water out to the point it's no longer dripping. The napkin should be moist but not sopping. Spread the napkin flat and then sprinkle as many seeds as you'd like to sprout. Fold the napkin over and put it in the bag with some kind of marking or label to identify the variety inside.
You check the napkin every day to see if the seed has sprouted. I hold the bag up to a light source, so the root is visible in silhouette. If there's a root at all, it's time to place the sprouted seed in a shallow depression in potting soil in a pot, then cover lightly and water in gently.
From there, it's a matter of keeping the potted seed warm enough that it can grow until it's time to plant out in the garden. I use clear plastic totes placed in a sunny spot outdoors and I haven't lost any seedlings to frost. You could also keep those potted seeds by a south-facing window in the house, but the lack of direct sunlight will make them leggy and weaker than if kept outside.
It was here in January, at the pre-sprouting step, that I was given the season's first surprise.
Potential Reasons This Year's Tomato Seeds Failed to Sprout
There are two main explanations for such a stunning failure with those early tomato seeds.
One could be that the paper towels were too wet. An academic paper from 1980 summarizes an experiment with sorghum and corn seeds to test the difference made by the amount of water in the paper towel. Between water concentrations of 2, 2.5 and 3 times the weight of the paper towel, the lowest amount of water gave maximum germination with a difference as much as 35 percent.
Another paper puts this result in context. Published originally in 2003, this paper summarizes research finding that soil contact—meaning how much the soil itself is touching a seed enough to transfer moisture—isn't all that important. It specifically cites research that found that at least 85 percent of the water absorbed by seeds can be directly attributed to vapor.
The second explanation could be the temperature. It might be that having piles of bagged seeds just got way too hot. UCANR has a spreadsheet with soil temperature conditions for germinating seeds. A heating mat like mine has no thermostat, and is probably made to have pots with soil set on top of them. Heat enough to radiate through a layer of soil is probably enough to cook seeds in little plastic bags, especially when 20 of them are piled one on top of the other.
The last factor is the seeds themselves. I've read that tomato seeds stay viable for only four to six years, but there's probably a lot of variation. A USDA publication from 1992 documents tomato seed longevity in decades, as much as 43 years with 76 percent germination.
The reason that I don't blame the seeds, as I've been known to do, is that germination was incredibly low both for seeds I've had in the cupboard for four years and for seeds I just received in the mail. There was no grand conspiracy to deny me sprouted seeds.
Just to be sure, in April I put a cheap thermometer in the middle of the pile of bags with the latest round of seeds and was surprised. The temperature was about 105 degrees, which is far beyond the maximum for sprouting tomato seeds. In my zeal to sprout so many varieties I ended up killing nearly all of them. Fortunately, melon seeds do much better at that temperature and nearly all of them sprouted just fine.
Incomplete Failure
No gardening season goes perfectly. At least, I've never heard of one. Last year in February we had an unseasonable heat wave that cooked about half of my healthy tomato seedlings right in their plastic totes. In late February I started the whole process over and my tomatoes did well enough that I wrote a whole blog post to brag about it, which unknowingly sealed my fate.
This year I've also had some early success. Last spring it was nearly impossible for me to grow a green-fleshed ayote squash. I ended up with only two viable plants and saved seeds from a single fruit.
This year, not only did almost all of last year's ayote seeds sprout, but so did the ayote seeds I just received in the mail. So did nearly all the melons I'm growing this summer. It was as if the gardening gods took pity on me and agreed that I needed some wins. I'll do my best to stay humble and hopefully avoid their future ire.