Cucumbers are fickle plants. Seedlings don't always sprout, and even if they do, they're difficult to transplant, and even if they're transplanted, there's no guarantee they'll survive the transplant. And finding the right cups each time is difficult. There's an interesting solution: growing cucumber seedlings in eggshells.
Seeds should be planted in late April – early May.
Preparing seedling shells
Make a hole 2-3 cm in diameter at the narrow end of a raw egg, pour out the contents, and dry the shell. Place the cooked shells on a tray, such as an egg carton. Also, prepare the planting soil, plastic wrap, and the prepared seeds in advance.
Planting seedlings
Fill the shells with soil, place 2-3 seeds at a time, and fill almost to the top. Place the shells in a tray, water, and cover with plastic wrap. Water as the soil dries. On the fifth day, the shoots should emerge. Then, remove the plastic wrap. Keep the seedlings warm for another two weeks, after which you can give them their first hardening-off period: take them outside or to an unheated room, keep them there for an hour, and then bring them back. Hardening-off should be repeated several times.
Transplanting such seedlings is very simple: you don’t need to take anything out, just lightly squeeze the shell until it cracks – and plant it whole in this form in the garden bed.
Advantages of shell seedlings
Besides eliminating the need for transplanting, which cucumbers dislike so much, eggshells themselves are rich in nutrients and will immediately nourish the plant. They will also protect against diseases and pests. You'll be delighted with the harvest!

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Winter
In 2019, I tried planting cucumbers this way... all varieties sprouted... this was my second sowing of cucumbers this year... the first batch was sown in snails and had already been bearing fruit in open ground almost since the beginning of June and are still bearing fruit... steadfastly withstanding this summer's bad weather (my good ones))... I have already planted cucumbers from the shell in a greenhouse... 10 pieces... (although I sowed more). They took root... fruited... it is August 12th outside.