Bit of a long shot but can only ask!

I need a large amount of potting medium and was offered as much as I wanted from very well rotted down compost heap.
I was initially told it was years of old grass clippings so thought the compost would do the job that I need it for.
Went along today and bagged up vast quantities of it. During the bagging process my friend who “ owns” the compost heap told me that there is also Biomass boiler ash in amongst the grass. OH! Now I am not so sure if the stuff will be ok for potting up mostly bog standard herbaceous perennials. I expect the ash will be alkali? and quite strong? But this is a guess. What I did not ask is roughly what percentage of the heap is biomass ash. When I got the bags home the consistency of some of it is a bit sticky but not too bad.I have excess leaf mould which I could mix with the stuff if that would help? What I don’t want to do is spend hours and hours potting plants up only for them to leg up.
If it was early in the year I would sow something like cress in it and see if it germinated and grew ok but doubt now heading swiftly into autumn whether it would germinate and anything I am going to be potting up is pretty well dying back now anyway.
Any advice would be much appreciated as if it is not going to be ok I will not spend another hard day bagging it up and bringing it home.

 

All I can say is a a school kid we grew cress indoors all year round.

I would think for a potting compost you can only expect this to be one component, and add other things like sand, perlite even garden soil and your leaf mould.
The only thing you wont have a clue about is the nutrient content of the finished article.

 

@hailbopp I'd Google it before you do anything with it, it might not be good for potting mix.looked it up but don't know how to put it on here.

 

Oh yes suppose I could set up my heated propagator and sow something in the compost and some in some Jack’s Magic I have left over. I am not sure if I have any cress seed that isn’t prehistoric but have a huge quantity of carrot seed which is new this year. How about I sow some of that and see what happens? or alternatively have a very healthy supply of Mange Tout seed so easy to spare some of that as well. The later usually germinates very quickly. Presuming I get germination in the suspect compost, how long before it is pretty safe to say the compost is safe to use?

 

Thanks JWK I will do as above today. Fingers crossed the compost is ok as it would save me a fair doze of cash if it is.

 

They might grow but what about what they take up as in bad metal and such like?

 

@hailbopp I would test it as has been suggested.
Given that biomass boilers typically burn woodchips, wood pellets, straw and some pelleted chicken manure I would expect the ash to be similar to wood ash, it will probably be alkali, but as composted grass can be quite acid it's unlikely to be a problem.
Being similar to wood ash you are unlikely to have much in the way of metal contamination that might cause problems.

 

Oh you gave me a laugh Pete, it was such a funny series.I grin every time I see a large chandelier . A friend of mine grew Mange Tout with great success one year, so much so they were served up to the family with monotonous regularity. Her 4 year old daughter was not impressed and at supper announced “ oh no not mangy towts again” ever after that we always called them just that in this household.

 

Well the experiment is under way. Mangy towts! planted and 2017 cress( did say it was prehistoric) scattered on the compost from friend and Jack’s Magic. Time will tell.I contacted my friend and asked her to give me a guesstimate as to how much grass to biomass ash. She reckons very little, maybe good, HOWEVER what was interesting is she told me that they have a gardener once a week to help as they have a huge amount of ground to mow and trees to prune etc. I have met him briefly and he was definitely a gardener not just a tidy upper or garden slaughterer that so many are these days. He has taken a huge amount of it, hmm me wonders if this stuff is a good fertiliser. He and I could end up fighting over the stuff! I will have to find out what he is using the ash for. My guess would be veg beds but I could be wrong. Perhaps in years to come if biomass takes off people will dry the ash and sell it as fertiliser?

 

I was put off eating mangy touts when one came open between the cooking and the putting on the plate process, it had the fattest maggot I've ever seen inside it.

 

Possibly on his fruit trees and bushes as wood ash contains potash which is good for fruiting, or he might be using it as a general soil conditioner particularly if on clay.
Let us know if you find out.

 

Never been a great fan of mange tout, not really one thing or the other, give me proper garden peas anyday. Also part of the fun is in the shelling of the peas. Although you then have to dispose of the pods; I did try peapod wine one year now 4 years later I taste it every 6 months and put it back in the garage as it still tastys very pea poddy.