Get them off the heat mat and take that dome off. Snapdragons are a cool weather plant and germinate at around 65 degrees F so they should never be put on a heat mat. Both the heat mat and humidity cover should only be used for germination. Once the plants are up they are not needed. The heat mat can burn tender roots and the humidity cover while great for keeping seeds moist for germination will invite damp off.

My friend complained that last year not 1 snapdragon seed germinated. I asked if she put them on a heat mat and she said yes. That's why you have no snaps I told her. You cooked your seed. Seed packages offer a wealth of info among which is the germination temperature

dowlinggram, I have a number of snapdragon sprouts that have been under lights in my cool garage. They look great for their age/size, but what do you recommend for thinning/planting out into larger pots? Thank you!