You’ve probably heard for years, as I have, that Napa Valley gardeners should wait to plant tomatoes until at least May 1. Even better: the second week of May when temperatures should be reliably warm. I had heard that tomatoes planted this late soon catch up with tomatoes planted much earlier, and may even surge past them. I always wondered if this was true, so I asked some nursery experts.
One nursery person advised me to wait until the soil temperature topped 60°F at a depth of three inches. So I purchased a soil thermometer.
Another expert told me to wait until the nighttime temperature no longer dropped below 50°F. For this information, you can install a wireless outdoor thermometer that records the minimum daily temperature.
Of course, for more certainty, you could wait until both criteria were met.
Being a scientist, I decided to try an experiment to see if I could get ripe tomatoes sooner than usual. Near the end of March, I purchased some tomato seedlings that were already fairly large. I transplanted them into one-quart pots and began putting them out in the sun during the day and bringing them in at night. Since I only had four plants, this wasn’t an onerous job. I planted them in mid April, when the soil temperature and nighttime temperatures were still below those recommended.
The plants developed well, and by the middle of May, they were large and healthy looking. By that point, the plants already had some half-size green tomatoes. My first tomatoes ripened just before the end of June when many of my friends’ plants hadn’t even set any fruit yet. The results surprised me (and a few others as well).
Even so, I don’t recommend that you plant tomatoes this early. It’s better to be safe than sorry. But I thought you might be interested in the experiment. To be scientific in your own tomato quest, you could plant one variety early, as I described, and then plant another of the same variety nearby but following generally accepted practices. You might enjoy watching them both develop and seeing which plant performs better.
Napa County Master Gardeners will lead a public workshop on Saturday, April 21, from 9:30 a.m. to 11:30 a.m., on “Growing Salsa.” Learn the tips and tricks for growing tasty tomatoes and peppers and how to choose the right varieties for your garden. The workshop will be at the University of California Cooperative Extension, 1710 Soscol Ave., Napa, and pre-registration is required. Class fee is $5.
Master Gardeners are volunteers who help the University of California reach the gardening public with home gardening information. Napa County Master Gardeners (cenapa.ucdavis.edu) are available to answer gardening questions in person or by phone, Monday, Wednesday and Friday, 9 a.m. to Noon, at the UC Cooperative Extension office, 1710 Soscol Ave., Suite 4, Napa, 707-253-4221, or from outside the City of Napa toll-free at 877-279-3065. Or email your garden questions by following the guidelines on our website. Click on Napa, then on Have Garden Questions?