I regulary re-use my JI style compost. The old compost will still have its structure but have lost most of its nutrient value. I add a small amount of bonemeal to mine.

So it is still good but just needs a bit of a boost. That's good. Saves work and saves compost too. Why bonemeal rather than a general fertilizer Bulbaholic?

Depends what you want to grow. If it's just bedding plants they should be fine. But not all plants like John Innes 2 as it holds too much water for them, eg certain alpines as I've found out.

Well perennials mostly and shrubby things.

Why use old anything, you've bought the plants, or grown from seed "did you look for old last years used annuals then?
You've removed the weeds etc & spent time making space for your plants "why not leave the weeds etc in the ground?

It's like you eating old used food, are you going to re-use
a pizza you've had sitting around for months or buy or make a new one?

You'r plants "like you" get what you feed them, if you want short cuts "buy plastic" if you want your young plants to look really good !!! Use the best,

Old compost can be used to spread over the bedding area to help lift the PH.
I myself when the end of the summer arrives empty verious troughs window box's hanging baskets etc etc all onto the compost heap or one of the raised beds to improve both. (I also use bone meal "slow acting fertilizer, & fish & blood) and these will still have some use in them.

as Bulbaholic said most of the good stuff has gone out of old J.I compost and its only true value is in holding moisture.

If you really want good healthy plants feed them what they need, (like humans)

There is JI compost and there is JI compost, Bendipa. It's quality depends on what is available to you, but I agree that most is very poor. The original composition was, approximately, 2parts 'good quality' loam, 1 part humus and 1 part grit (plus nutrients). As early as the 1950's the supply of 'good quality' loam was fast disapearing and this is why peat based composts were coming to the fore. Nowadays the only way to get this 'good quality loam' is to make your own as the commecial stuff is just like silt.
I stopped buying JI many years ago and make my own using one part 'pretty good quality' loam, 1 part leaf mould and one part grit. I use this for all my pllants which are mainly alpines and bulbs.
I have no hesitation in re-using this compost base with extra nutriens added, Dungy. As long as the old plants were healthy there is nothing wrong with the material. The purpose of the base compost is to hold the plants upright and store some water and nutrients.

John Innes composts, 30 years ago, should not be used once they were over a couple of months old, but since they changed the nitrogen formulation, that's no longer a problem, so you can use your old compost, Jonathan. Personally, I'd add fish blood and bone in preference to bonemeal, but if you've not got any, a handful or three of Growmore will do the job.
One other thing - by 'old' I'm not sure whether you mean old unused compost, or old used - if its been used, there's always a risk it may contain pathogens, but most of the time, we get away with it.

If as bulbaholic has said that JI is for holding up your plants then "DONT" buy it, go for the cheaper compost that is only a base with next to nothing in it,

As ive said many times, No free meals, If you want good healthy strong plants use only good compost with all your plants needs,

the information ref the make up of whats in the bag is on the side/ or back of the bag the compost is vacuumed packed in.

I myself make my own compost most of the time using verious mix of the likes of

blood/fish/bone/sand etc and have little if any problems,
But i dont use already used compost the following season,
Not after all the prep in sowing and getting the plot's ready for planting,
I want my veg to be the best, my rose's to bloom & smell like a rose should,
If i started to cut corners i only have my self to blame and its me who dips out on a season's growing,
Gardening will not allow you to go back time & time again,
It's as much of a timing thing as it is doing it right first time, Very few second chances with a lot of what you grow.

No idea what Dungy is on about again, but rejuvenating compost to be used again for plants is perfectly acceptable and you will end up over time with a mixture far superior to anything bought nowadays from garden centres.
I should know, I've been doing it for years, saves a fortune, and in no way is it cutting corners.
If you look here

http://www.gardendirect.co.uk/garden-care/fertilisers/general-fertilizers-chemicals/b.t.d.-fertilizer

that will make the same fertiliser formula as JI no's 1,2 and 3.

You folks could write me an encyclopedia. Thank you so much for advising me. Am planting Pinus Mungo's. Lovely.

I did mean old used compost Bamboo. It has been outdoors in my containers open to the weather for a long time. I've have an idea that with time it will evolve closer to something like natural soil,- rain, bacteria, fungi. But I'm no expect like some others.

Well I reuse used compost frequently, Jonathan, unless I'm aware that whatever was planted in it before had a problem, specially a fungal problem (pansy spot, that kind of thing). You're right, the stuff will be closer to ordinary soil, but any pathogens are contained in a pot, which they aren't in open ground, so that's the risk. To be honest, I think, in 30 years, I've only had 3 occasions where I should have changed the compost because there were problems. That might sound like a lot, but bear in mind I've probably planted a lot more containers than anyone not working in gardening professionally. Sometimes, its down to luck of the draw, lol

There are also instances of freshly bought compost causing problems to plants.
As to the compost being overwintered and out in all weathers, no problems,now is the ideal time to freshen it up.
Just empty it all into a wheel barrow, run your fingers through it to remove any green stuff/weeds in it, then mix in your fertiliser.
If you go to a garden centre and buy sterilised top soil, that can be mixed with it to mimic garden soil.
Or you can sieve it, mix it with horticultural sand, and make up seed compost.
The possibilities are endless.

Sadly not in Jonathan's case because of disability. Jonathan, turn the soil in the pots over with a hand fork as best you can, right down to the bottom if possible, breaking up any old root material, removing large lumps of that if there are large lumps. Now add your fish blood and bone or Growmore and fork that over again. Soak if necessary and then plant the next day, or the same day if the compost isn't bone dry. You might find you need to top up the compost though.

I excavate with a soup ladel!

Well, whatever works! I use my breadknife for cutting up rootballs, so the kitchen can be a useful resource area, lol

Try mixing your composts in a food processor. It'll paste up the worms a treat.

The best compost mixer is in fact the tumble dryer. All you have to do is wait for the wife to go shopping.

She'll want a divorce! Lots of gardening goes on the kitchen. I've germinated seeds in the fridge. Dibleys plants grow above my sink.