Allotments 4 All

I've noticed a green mould developing on top of the compost on my greenhouse plants, is this harmful to the plants and if so how should it be treated/avoided?

this sounds to me as you have been over watering be very care full with this as can cause infection to the plants two ways you can address this

Firstly with copper solution (fungaside)
secondly repot with fresh soil id even go to the extent of rinsing the roots under under rain water or tap water then re pot

I wouldnt worry too much, green mould/algae does suggest too much water / too little light but its unlikely to do damage, try to address the light / water balance and the plants will be fine.

It shouldn't do any damage, but it is a sign that the pots are too wet.

I sometimes get one or two plants with this in the greenhouse, they all get a massive shared watering and obviously it is too much for some. Not enough for others.

I just get a thin stick (kebab size) and scrape the top, like a mini dig over.

I try to use a little house plant can to give all the plants separate water to avoid the too wet/dry problem when I can but it is time consuming.

Thanks all, i did a  bit of scraping off last night, the warn weather appears to have dried out the green mould, it mainly affected the Basil, killing most of the new seedlings, but those that have survived seem strong.

Some composts seem more prone to this developing than others. I use a table fork to 'hoe' the mould away, the main danger is that it's not so easy to tell whether watering is needed. The problem disappears once the plants are in larger pots.

You get good idea.but I want to contat you for detail.