Tomato Patch: Exposing Seedlings to Reality

Sungolds and Juliets--growing fast now

This was “toughening up week” at the Tomato Patch.  Late Sunday afternoon I moved my three-week old tomato plants from their warm growing racks under fluorescent lights in our utility room to semi-protected containers on the east side of our house, so they would get increasing amounts of sunlight and be exposed to breezes that would help stiffen their stems.

This toughening up is called “hardening off,” which the Maryland Master Gardener Handbook defines as “the process of gradually acclimatizing a plant that has been raised indoors or in a greenhouse to harsh environmental conditions in the garden” (Chapter 17, “Vegetables,” p. 411).

I would be happy to transplant my tomato seedlings directly from utility room into the garden, but the risks would be high.  If subsequent days were warm with intense sunshine, the tender plants could sunburn—just as I would if I went to Ocean City and lay the whole first day in the sun without sunblock lotion.  Also, a sudden spring thunderstorm with wind and a downpour could twist and bend the tender stems and smash the plants to the ground.

So that’s why gardeners who start spring vegetables from seed indoors “harden them off”—“gradually acclimatizing” them to the cool, sunny, breezy world, though I hesitate to call our garden a place of “harsh environmental conditions.”

"Gradually acclimatizing"

“Gradually acclimatizing” for my plants meant this: (1) I put them in open plastic storage bins that protected all but the tops of the tallest plants from wind gusts.  (2) I took them out late Sunday afternoon for their first direct-sun exposure, and the afternoon shadow of the house shaded them after about two hours.  (3) Since it rained Monday and Tuesday, I kept the plants under the roof but on the edge of the porch, so they got bright light but weren’t battered by downpours.  (4) When the rain clouds exited and the sun shone brightly, I moved the plants a foot farther from the house each day so they’d get ever-increasing direct sunlight.

I planted the seeds in cups on April 19.  The shortest plants (Celebrity) were four inches tall by Wednesday and the tallest varieties (Juliet, Sungold, and Amish Paste) were more than six inches and growing at least one inch a day.  I was beginning to think they were clones of Jack’s fast-growing magical beanstalk.

The rains earlier this week were important to the Tomato Patch.  Early spring 2012 was especially dry.  Year-to-date rainfall before this week was about six inches below average.  Lack of moisture can be a factor contributing to blossom-end rot in early tomatoes when garden soil has insufficient moisture for the plants to move calcium from the soil to the developing fruit, so I’m hoping I’ll not have the significant losses that I had last year from that disease.

I’ve already written in my Garden Notes that I should start my tomato seeds a week later in 2013, around April 25, so they’ll be ready to transplant around May 25.  Tomatoes are a tropical plant and really thrive best in well-warmed soil, which means the opportune time to set them out here in Central Maryland is near the end of May or even early June—though that may seem like heresy to gardeners who set out their tomato transplants in late April or early May.