BTW the heat-retaining black plastic tray didn't help. Start seedlings under flourescent lights whenever possible. It is easier to monitor their health and notice problems before they progress past the point of no return. Outdoors under direct sun, you might leave them in the morning and return to find them dead by dusk. Once you 'learn the plant', you will be able to judge when to put them outside, and how to manage them. Rockwool outdoors isn't going to work in 99.9% of cases. It requires frequent waterings (like every few hours frequent) to stay moist in hot weather.