You may recall my experiments with low tunnels for squash and low tunnels for sweet potatoes. I’m always looking for opportunities to get an early start on spring, or to hang on to the last breaths of fall before winter takes hold. Low-tunnels are an easy and cost effective way to extend the growing season and this year I’ll be experimenting with low tunnel tomatoes.
I got really solid germination from my tomato seeds this year. Soil blocks made from 1/4″ screened Pro-Mix and a heat mat set at 82-F gave me 100% germination. A first, in my experience. To-wit, I also started some heirloom Brandywine Tomato seeds that I bought in 2010. That seed is over 5 seasons old and it too germinated vigorously, 100%. I always germinate way more seedlings than I need, to mitigate the risks of poor germination, mice, weak starts, etc. and I cull them down to only the strongest contenders. This year, though, I decided to run an experiment with my extra seedlings. Last week I planted out 8 seedlings in one of my planned tomato rows. That’s right: tomatoes, outside, in April, in New England. Because “Danger” is my middle name.
The little seedlings had just formed their first true leaves and were looking sprite and happy in their soil blocks. There they were, basking under the glow of full-spectrum grow lights in the cozy warmth of our house. That is, before I ruthlessly slammed them into the cold wet ground outside at high noon on a full-sun day. No hardening off. No coddling. Boom, welcome to nature! Seriously, I was trying to do it as “wrong” as I could, just to see what happens.
My expectations are not high, but I’m not stupid either. I put a plastic low tunnel over them. Ah the wondrous versatility of a low tunnel greenhouse! Over the past few days I’ve had to open the tunnel in the morning and close it in the afternoon because on a 65-degree sunny day, the temperature inside the tunnel goes straight to 100-degrees. It’s vented on both ends, but it still seems to maintain a 20-30 degree temperature differential under direct sun. And I sure don’t want to cook the seedlings.
I will continue to monitor the weather closely. If there is even a risk of a light frost, I will cover the tunnel at dusk with a heavy tarp, which will reduce how much heat is radiated to the night sky. If there is a risk of a hard frost, I will “bucket” the plants, covering them with a 5-gallon bucket and also covering the tunnel with a tarp. That should be enough to get them through 1 or 2 nights of frost, should that happen. The grass is just starting to grow too, so I might even be able to get a bale of clippings for mulching that bed this week. Decomposing grass clippings under a low tunnel should add an enormous amount of heat and protect the seedlings as they cool down overnight.
If these don’t make it, it will be sad, but I have enough seedlings to replant. My control group will be the rest of the seedlings that I will pot up and maintain inside until the end of May. Eventually the seedlings are going to outgrow the tunnel, but hopefully by that time the risk of frost will have passed, and I will have a row of tomatoes with a 6 week jumpstart on the season. In New England, the Holy Grail of Gardening has been fresh, garden-grown, vine-ripened tomatoes by the 4th of July. I will come back with a report on which plants did better, and produced earlier. So far they seem to be happy. Time will tell…