If Goldilocks had a garden
Irecently heard from a reader who was wondering why some things just wouldn’t grow for her. Linda Donnon, from Downingtown, wrote, “I have just recently started veggies. I have had lots of success with flowers, but veggies are another story and I’m not sure what I’m doing wrong, but I have not had success with anything. I can’t even seem to get beans to germinate!” I empathize with Linda. It’s always so disappointing when we do the work of preparing the soil, planting, and watering, only to have nothing happen. Especially when it’s beans. They grow like crazy, right? It turns out that beans are more fragile than we’d think. In my own experience, I’ve had bean seeds fail to germinate. I’ve also had bean seeds that sprouted but failed to produce leaves.
One of the main causes of a poor outcome for beans, and for many other vegetable seeds as well, is soil temperature that is too cold. The rule of thumb for putting vegetable plants out into the garden is to wait until “after the last frost date.” In our area, that is April 30, and I usually allow an additional two weeks, just to be sure. But here’s the cautionary part: although the air may be deliciously warm by May, the soil is likely to still be cool. For some seeds, this is a serious challenge, so I suggest taking the “Goldilocks” approach to seed planting, looking for a soil temperature that’s “not to hot, not too cold, but just right.”
What is “just right?” It’s different for different plants. Some seeds, like lettuce, beets, carrots, and spinach will germinate at soil temperatures of only forty-five degrees. By all means, plant them early and get a jump-start on your garden. Other seeds, however, like melons, squash, and beans, need the soil to be at least seventy degrees for germination. In fact, for beans, a temperature of eighty degrees is optimum. Melons and squash prefer a warm ninety degrees. And even lettuce, beets, and carrots prefer a much warmer soil temperature.
The remedy for poor germination then, in many cases, may simply be to wait a little longer into the season when the soil is warmer. You can also essentially speed up the season but setting up raised beds and/or laying down black plastic.
How do you know what the optimum soil temperature is for different vegetable seeds? The folks at Gardeners Supply Company have made it easy, with a chart on their website (https://bit.ly/2xhE3kQ).
Like other germination charts, this one shows the optimum soil temperature for different vegetable seeds, along with the minimum and maximum temperatures at which seeds will germinate. With good seeds, at the optimum soil temperature, you can expect 100 percent germination or close to it. The farther you deviate from the optimum, the lower the germination rate will be.
But what I love about this chart is that it also indicates the practical temperature for germination. This comes from Dr. Jerry Parsons, Extension Horticulturist at the Texas Agricultural Extension Service, who identified what he calls a “realistic” soil temperature for germination. As described on the website, “This is a soil temperature at which gardeners can expect good germination and strong early growth. Germination rates may be at 70 percent rather than 100 percent, but you can just sow the seeds a little more thickly.”
Problem solved! You can get out and plant earlier and simply adjust your sowing density to allow for a lower germination rate. You can also plan to fill in any blank spaces a little later in the season, when the soil has warmed up more.
Note: It was gratifying to have so many readers request the list of upcoming plant sales featuring native species. Many also mentioned that they plan to attend the talk about pollinator-friendly species at the Exton Library on Monday, April 30, 7 p.m. For the list of plant sales, email me at pamelacbaxter@gmail.com Pam Baxter is an avid organic vegetable gardener who lives in Kimberton. Direct e-mail to pamelacbaxter@gmail.com, or send mail to P.O. Box 80, Kimberton, PA 19442. Share your gardening stories on Facebook at “Chester County Roots.” And check out Pam’s new book for children and families: Big Life Lessons from Nature’s Little Secrets. Available at amazon.com.