Rocket dying

[Marb67]

Well, I just can't even grow simple Rocket without some failure. I carefully sowed them and sat in the kitchen window and now the stems are going thin and wispy, falling over. This can't be damping off because I watered from underneath, not from above and the conditions have been airy in the window. Probably too late to sow more so covered with more soil and hope the others don't go the same way. Put outside in the raid in hope it will harden them off.

[ameno]

It's damping off. I don't know why you keep insisting that it can't be this or can't be that. Gardening isn't an exact science, and sometimes you can essentially just be unlucky.
In your case, the seedlings are really leggy due to not getting enough light. This probably made them more prone to infection, as leggy seedlings are softer and fleshier, and thus easier for fungal infections to get in.

Also, it's nowhere near too late to sow more. Rocket is ready in about 6 weeks (less if you grow it as a cut-and-come-again crop), so you can sow all the way up to September, maybe later.
I would strongly recommend raising brassica seedlings outside this time of year, though (you can still sow them in a pot, just leave the pot outside). It's more than warm enough outside, and as you have found with yours, they don't get enough light when raised indoors. They will be far less likely to damp off outside, too. Just try to keep the pot somewhere out of reach of slugs (I keep my purple sprouting broccoli seedlings on a high shelf).

[Marb67]

But how can they get infection when it was watered from underneath in new compost and clean pot ? That's my point.

[ameno]

It's a fungus. The spores are airborne. They are everywhere, so all you can do is do things to help reduce your chances of infection. You can't completely prevent it with 100% effectiveness.

[rary]

Certainly not too late for sowing rocket, I will be sowing some seed tomorrow, if I get the chance, if it will do on Monday, some outside, some inside, in the greenhouse actually so that there is plenty of light which should avoid them being leggy

[Marb67]

Certainly not too late for sowing rocket, I will be sowing some seed tomorrow, if I get the chance, if it will do on Monday, some outside, some inside, in the greenhouse actually so that there is plenty of light which should avoid them being leggy

Plenty of light yes, but the heat is too much for them. they would just bolt.

[rary]

Marb if inside the greenhouse is to hot you need to provide shade, a bit contradictory when talking about legy seedlings, but you could use a sheet of newspaper to provide shade, also try to create a through draft by opening doors and windows, sit your seed trays on a water tight tray and if you don't have capillary matting again use several layers of newspaper soak with water and sit the seed trays on this keep the base layer moist

[Marb67]

Don't worry, the greenhouse isn't getting warm these last few days with the awful Autumnal weather. Had to take the white mesh for shading off the glass to use on the runner beans to stop sparrows shredding the flowers. Robbing Peter to pay paul as they say.