FIMBY: Time to give seedlings some more space

This is another in our “Food in My Back Yard” series, dedicated to edible gardening.

Are your seedlings yelling at you yet?

If, like me, you started tomato seeds in early February, you probably have plenty of little tomato plants that now need more space. Think of them as pre-teens -- bugging you, begging you to let them grow and expand their horizons, but nowhere near big enough to be settled into their future lives. They're in an awkward transition phase, and you have to help them as they are, not as you wish they were.

Plus, it's still really cold outside.

Tomato plants need consistent overnight air temperatures above 50 degrees. The Sacramento area isn't close to that yet: This morning (March 18) the region averaged a low of 38 degrees. Today is the last average frost date for our area, but we had overnight temperatures in the 30s as late as April 7 in 2024.

Soil temperatures are even more important. Tomato roots need soil temperatures above 60 degrees, preferably 65 to 70, say master gardeners and university research. Planting in soil that's too cold will stunt those seedlings you've fussed over, and they won't catch up,  even with Wall o' Waters or any other warming gadget you can think of.

So here's how to move seedlings for tomatoes (and peppers and eggplant) into new temporary quarters:

1) Prepare a nourishing potting mix. In a 5-gallon bucket I combine potting soil with almost an equal amount of compost, plus, if I have enough, some worm castings. I add a couple handfuls of perlite and vermiculite, because even good potting soil never seems to have enough of either, which keep the soil light and aid drainage and nutrient retention. An alternative to vermiculite is any leftover seed starting mix I have on hand. Mix well!

 2) Prepare the new homes. I often reuse small plastic pots and large nursery sixpacks, but they must be scrubbed clean. A 1-to-9-part mix of chlorine bleach and water will sanitize them of any lingering bacteria or pathogens. Rinse and air-dry (in the sun if it's out). New small pots also are great if you can find them (try a dollar store).

3) Decide how to label the plants. It is way too easy to mix up tomato plant varieties when doing a big day of transplanting. (Ask me how I know this.) I gave up on plastic labels that you stick in the soil -- they flip out of the pots far too easily. I now use painter's tape attached to the pot as the label and a Sharpie pen to write the variety. If the pot is light-colored, sometimes I'll write the variety right on the pot. That's good for plant sales or swaps, especially. 

4) Choose where the repotted plants will live. They still need light and water, plus 6 hours of darkness. For now, I try to keep them all inside, even if I have to rotate them into the best growing spots in the house. If you're able, move the plants outside daily (when it's not raining) for gradually more time to harden them off. Tender plants will be fried by too much direct sunlight, so putting them in open shade for an hour or so is a good way to start. Note: Even a gentle rain can spot the leaves, too, I've discovered.

Another option is to place them in a covered outdoor "greenhouse" (mine is three racks with a zip-up cover that opens on each shelf) or in a cold frame. Bunching the plants together does help raise the temperature inside; a string of old-style Christmas lights can also help, if there's an electrical outlet nearby.

5) Fill a small-spouted watering can or pitcher with water for the plants once they're moved. Watering direct from a hose is usually too much for such baby plants -- you don't want to drown them.

Now you're ready to move the seedlings.

First, label the pot or sixpack with the variety you plan to transplant. I started with 6 Better Bush tomatoes, which each got their own 3-inch pot. Put about 1 inch of prepared soil in the pot, and check the level for the seedling that will go in it. You want enough of the stem in the soil to encourage new roots along the stem, so plant the seedling deeper than its current soil level. But leave 1 to 2 inches of stem "above ground" so the leaves aren't touching the soil.

Once the bottom level is OK, carefully remove the seedling from its container -- but don't pull it out by the stem! You risk ripping it off its roots. If all the seeds germinated and there are more plants than you need of a variety, nip the stems of the extras at soil level with your fingernails or small garden snips -- again, don't pull out them out.

Gently push the seedling from the bottom of the container or use an old teaspoon to gently dig it out of the container. Loosen the roots, if they're starting to bunch up, and place the seedling in the new pot.

Now fill in around the stem until the soil reaches the level mentioned above. (Don't fill the pot all the way to the brim; you need some space for watering.) Then tamp the soil down with medium pressure, and water the plant thoroughly -- the water should drain out through the bottom.

Once all the plants of a particular variety are repotted and watered, move on to the next group. In 5 to 7 days, once they've acclimated to their new spots,  some half-strength diluted liquid fertilizer (fish emulsion is my choice) is an option. 

Tomatoes transplanted this week should be ready to go into the ground or their final large containers the latter half of April -- depending, of course, on the weather and soil temperature.