Hi Tracey, are you sure you need to rake out the ash from your new burner? I suggest you check the instruction manual to see if you do.
Many models need a layer of ash in the chamber to help control the rate of burn (no ash = too hot = damage) and you will be surprised how the ash packs down to almost nothing.
Having said that, you might get a build-up that needs to be removed occasionally. By all means add small amounts to the compost heap but keep fresh ash away from raspberries, other fruit and the potato plot. Have a look at the advice on the RHS website - http://apps.rhs.org.uk/advicesearch/Profile.aspx?pid=621
Be cautious about the wood you burn as well. Throw away ash from treated timber, it might contain harmful residues. Find a source of properly seasoned hardwood to burn, or buy a load in to season and use uberlogs or "heat logs" for the first year. This will also be in the manual, so have a read.
Finally, enjoy your new burner.