I spent this and last weekend potting up most of my seedlings. Some were more difficult than others.
For example, Pulsatilla and strawberry seedlings have extremely long and delicate taproots (in the picture, the roots are almost 4 inches long, while the above-ground portion of the prairie crocus less than 0.5 inches tall). Any side branches of the main taproot are pretty sparse. This makes transplanting them rather difficult. The long taproot tends to anchor the seedlings very solidly in the medium while the unit is in the cell, but once extracted, any medium crumbles away immediately. Damaging the roots or stem is easy if the extraction and repotting process isn’t done with care.
Next year, if I do sow these seeds, I’ll probably start them in-situ rather than in seedling packs.