Clay lumps in bought Multi Purpose Compost

TheSouthernGardener

Hi All,

I put some bags of multi purpose compost over my raised beds last week as a means of topping up the nutrients and mulching the few plants I have growing in each bed. We then had loads of rain for whole of the following week so I didn't go near them. Then yesterday I went into the garden only to see loads of pebble sized chunks what i initially thought was maybe cat poop all over all of the beds ,but it is very light grey in colour and of a very clay like consistency, but what id like to know is has anybody ever had this issue when buying store bought bags of compost as i've never come across this before.Thanks 

nick615

Not in my experience - but one bag per year is about our total usage.

Posy

I have had the odd lump like this but not so many as you seem to have had. On the subject, composted manure or garden compost is much better for the beds than multi purpose compost which is really designed for pots.

Fairygirl

I've not had the problem, but it certainly won't do any harm. Unfortunately, lots of commercial compost is quite variable.
As @Posy says, home produced compost and/or manure is slightly better for topping up raised beds of any kind as it improves the structure, but spent compost from pots, or fresh compost is also ideal. Not everyone has large amounts of home made compost to use. 
Fresh compost adds nutrients, which is also needed in many instances, so it certainly isn't a problem, but if used at this time of year, most of the nutrients will be lost by the time you plant or sow, so bear that in mind if you're planting anything which needs food. 

Chris-P-Bacon

I've seen it MPC quite often. It's likely to be silt - especially if it's peat based compost. Peat is produced from former wetlands so is often found above silt or clay.

*Astrantia*

I’ve found clay in compost before, I can’t remember the brand, I was using it to pot up some seedlings and was surprised to see a lump of it!

BobTheGardener

I've seen it in some bags of 'with added JI' type composts and assume it's part of the loam mix which is added.  The screens they use to sieve this stuff have to be regularly replaced as they wear through, so some larger lumps will get through towards the end of its life.  Last year, out of 30 bags from the same batch, a couple had several large clayey lumps, but the rest were fine, so seems a bit of a lottery.  The odds aren't too bad though, if that sample of 30 is anything to go by, but that's not much consolation if you only buy one bag and are unlucky. 

Astro

I have only once and that was recently, not 100% it was clay but it sure seemed like it. It was a bag of peat free from wilkos if I recall and had quite a mixture of wood chip, gravel and the occasional pea sized bit of clay which was a surprise.

Fairygirl

It certainly isn't going to cause any problems. If anything, a bit of clay added to beds is a good thing 
It's a nuisance if you need it for seed sowing, because of having to sieve lumps out, but a lot of compost needs that anyway. 

As @BobTheGardener describes, re the screens, that seems to be the likely reason. I suppose we don't tend to think of that.