I dunno, I've read that some people have found it's too hot, I used FFOF for two years and I germinate in the substrate, my girls never burned and I have a 100% germ rate across about 20 different plants. So, personally, I do not think it's too hot for seedlings, just don't feed for about 3-4 weeks, the soil is pretty rich and can last a while before you need to add more nutes.