Posted: 15/02/2017 at 12:53
keeping your greenhouse as clean as possible is the best starting point Emma. In autumn a thorough clean with a disinfectant is essential I think. Equally, those pots and trays must be washed in strong disinfectant..I use bleach. And use fresh compost. Compost needs to be reasonably moist but not wet .and seedlings need space and good ventilation.
Opening greenhouse door may not be wise.....if the weather is cold your seedlings will suffer.
Sowing too early is a mistake we all tend to make but later sowings in warmer conditions will cope better.
Not sure of gh heater either.........it can create areas of condensation to the detriment of seedlings. I remember many years ago when we had an unusually cold winter someone lost all his plants in his heated greenhouse. In contrast mine surivived in a cold greenhouse. my plants were kept drier than his were I think !!
Removing dead foliage and good spacing is all you can do now. Cheshunt Compound was an excellent product to help prevent damping off but I think this has been discontinued. Resist the temptation to water repeatedly.
you dont say what your seedlings are but a later sowing perhaps!