Having already posted on thinning seeds by cutting down the weaker ones I wanted to show another way to thin out without killing all those other starts. While planting my starts this year, I made an incorrect assumption on the germination rate of my 4 year old tomato seeds. At 4 years, conventional wisdom says that the germination rate should be pretty low (like 10-20% of all the seeds planted) so of course I planted quite a few in a single spot (between 4 and 10 seeds).Well because we stored our seeds in plastic Ziploc bags inside a sealed mason jar in a closet on a high shelf to be out of the light, we were able to achieve a fairly high germination rate (of 80%). Now when you expect 10-20% and get 80% you have quite a few tomatoes to get rid of (about 60 starts) and it just breaks your heart to cut them all. Now splitting up the sprouts does not work for all starts. However, since these were tomatoes plants and tomatoes are known for be very happy with repotting and root disturbance, and these were still very young (seed leaves and perhaps the first set of true leaves just starting to bud). I decided that instead of cutting them down I would just knock off the dirt from their roots and repot them into a seedling starting tray.
So first I took my hand and gently dug under the plants to loosen the soil and bring up all the plants at once. Then because the soil was loose, I slightly threw the all of dirt up and down in my palms until the tomato seedlings came apart. With each plant separated, I made a deep depression (2-3 inches) in the dirt in the seed tray and placed most of the plant (including stem, this depth will also vary by plant – in general nightshades and squashes love to be replanted deeper) and replaced the dirt. I then placed the tray into the grow box to allow the plants to have the least amount of stress in their encounter.