Potato Onion seedlings

I was lucky enough to receive some seed of Kelly Winterton's potato onion seed. With some nurturing, I've got about 15 seedlings up. I've held back the majority of seed to sow next spring, but just had to try some over autumn.
Since I'm going on holidays, I've planted half in the garden, and entrusted half of the seedlings in a pot to the green hands of my mother, who will look after them in my absence.

I've also got one seedling from the topset onion plants that I assiduously de-bulbilled over summer, trying to induce flower set. About 10 seeds resulted, most of them rather thin and weak looking. I got one seedling to survive, and am wondering where to plant it with a chance that it will survive 3 months of neglect.