Mouldy Compost?

No, dont chuck it, if it is overwet you will know, often they can be overwet if outside, but in my experience that is usually if you buy early spring, that way it has spent the winter outside.
If it is overwet it is difficult to use.
I usually wait a while if I can, so as to buy new stock.

Never found an over wet bag at this time of year.
but have found light white fungal growth, which disappears when the stuff is put into pots.

 

Ah! But I have. Local well known GC has a large batch of extremely wet bags of compost. Offered a discount but declined and went elsewhere.

 

But re reading the OP, the sack was sitting open in a greenhouse when the mould appeared, so, only guessing, but not overwet.

 

Yes that's correct. When I opened it it was lovely, dark and rich looking. After a week left in the greenhouse it had developed the light white marks.

 

I still say stir it up and forget about it, compost is mostly organic material and personally I'd be more worried if fungi was unable to survive on it.
Fungi grow and form under certain conditions which alter once it is removed from the bag and used.
If the whole sack was riddled with white strands that would be something different, but even then it could possibly be a beneficial fungi, or at least one that doesn't harm plants.

 

I'm with @pete on this.
It was only on the top if I understand correctly? I've found several branded composts to be prone to this if they dry out, both in the bag and in the pot. I put it down to 'calcification' (for want of a better word) of the additives that are put in by way of feed.
If you're unsure do the 'milk test' - if it smells faintly sweet it is fine, slightly sour then it is off.

I also sort of agree with @Scrungee regarding seeds. I rarely sow seed in compost nowadays but when I do I run boiling water through it and then microwave it for about three minutes (depending on the size of the pot) before I sow anything into it.

 

Apologies for late reply, but I'm new to this site.

Mould/mildew in compost generally is an indicator that the enhanced process of composting is not yet complete. In most cases it is harmless, however if in doubt....cast it out. In some cases semi decomposed compost can actually prove to be harmful to some plant subjects. As an example. Lilium bulbs are hungry beggars. They are very prone to rotting. Yes. They are prone to becoming victims of semi rotted/de-composed matter. Like I say. Should you find some compost in a pre-semi state of decomposition. Leave it to one side.

 

IMO commercially produced compost is now big, big business. More than likely most of us gardeners first contact with 'compost' might have been some outdoor container in which the dining table left overs went, also the kitchen waste.. Do you remember the smell when you disturbed it. The the garden compost heap/pile started to take shape. As we dug the soil over, weeds and any remaing crops would end up on, the compost heap. Perhaps later still. A gardening friend might have suggested we don't add some perennial weeds to the heap. Later still, we discover that leaves even from our favourite shrubs along with disease, bacterial and or viral infected should be gathered up and burned.

Yes gardening is so interesting and as long as you are willing to live and learn. Suddenly a brand new world opens up.Gardening enthusiasts tend to go OTT. No offence intended.

So you have some seeds, plants, bulbs etc. What compost? Wow so many to choose from. Now we take heed of what others say. Many garden centers promote their own, so be it. Usually the price tag dictates. Hence we usually refer to products we have personally used.

First and foremost. This present day thing of compost etc to me is simply, recycling. Perhaps some inerlectual will be record in the annals of history as saying. Keep it moving, pass it on. This is what makes the world go round. Down to the critical nitty gritty.

As a retired proffessional. Over time I have used, tried tested many commercial brands. I found for instance. Levingtons little more than,'early stage' leaf-mould. Visiting numorous GC's I have sampled their own product. B&Q poor, little more than floor sweepings. Yes at the end of the day I prefer JA Bowers. It is wholesome and well balanced. Always remember that whatever you intend to grow in this compost. Prefers a certain pH soil value. Price is one thing,long term benefits another.