By Anniejess
United Kingdom 
This year my tomatoes germinated well in March but have made little progress since. They've been in a frost free greenhouse and are still alive with a good root system. What has gone wrong, please? I save seeds each year and grow about 8 different varieties - could they gradually be weakening? All other seedlings and young plants seem fine.
17 May, 2016
Answers
I too set my usual 12 toms in March exactly as you did. They grew 3-4 of an inch tall and didn't budge from there. So assuming they'd failed I set another 12, which caught up with the others, then stalled too.
But 10 days or a fortnight ago when the weather altered dramatically they grew rapidly and are now very healthy. I'd bet yours have too. I won't set them as early next year.
20 May, 2016
Previous question
No, I don't think your tomato genome is weakening. Some of the heirlooms I've grown go back hundreds of years. If there's anything that will slow down a tomato it's insufficient light & heat. Then check for sufficient space & nutrients to support vigorous growth.
18 May, 2016