My friend Sue has asked a couple of eminently sensible questions, which are worth answering in a bit more detail. Firstly she is wondering:

“When to remove the propagator lid, I have a memory of waiting till they have two leaves.”

Two leaves is good – though be wary of the two leaves that first appear.

Each seed has inside everything it needs to germinate, which includes ‘cotyledons’ – simple-shaped, baby leaves. These are enough to get the plant photosynthesising for a bit of external food, but are too feeble for everyday life. A bit like milk teeth in humans.

Most cotyledons are ‘dicotyledons’ (with two leaves) but you do sometimes get ‘monocotyledons’ with a single leaf – a typical example beings sweetcorn. You can remove the lid when they look stable but don’t pot-on yet.

While a plant still only has cotyledons it’s still relying on the seed for nutrition. You need to watch out for ‘true’ leaves. These will be obvious – they look like the leaves of the adult plant – in the case of tomatoes here, they are jaggedy, ‘compound’ leaves (in clusters). Once these arrive you know the plant has started fending for itself. It is still very delicate – it is, after all, only a toddler – but it is safe to move it into a (slightly) larger pot of its own.

Sue also says  “Inside the ones in plastic bags is looking a bit hairy, I am assuming fungal, should I be airing them?”

Yes, this does sound like there’s a spot of mould going on. You do need to introduce some air, and quickly. Maybe leave off the cover for a bit.

This is probably due to the soil being a bit too wet to start with and not enough air in the top. You have reminded me of a technique I learned off a Geoff Hamilton programme bloomin’ years ago:

Get a smallish pot for your seeds, half fill it with damp compost.

Add your seeds. As a demonstration I’m doing some cucumbers. The seeds are medium sized, so I’ve just put three in the pot. Eventually I’ll pinch out the two weediest looking specimens. Barely cover with some more compost.

Get a clear or translucent sandwich bag (in this case I’m using a plant carrying bag) and put it upside down over the top of the pot

Secure it with a couple of rubber bands.

With a drinking straw (I’m using a nice earth-friendly bamboo one, but anything will do) inflate the bag by blowing into it. The rubber band should keep the air in; you can reinflate as necessary.

Put the pot somewhere warm and bright. Keep an eye out – first signs of mildew, give it some air for a few hours then repeat the process.

Thanks for the questions Sue!