Hi Amy, yes as much compost and organic matter as you can. Your site sec may have a pet farmer contact who will deliver.. we pay about £25 a ton (although I have never weighed it!) or a Mushroom farm wishing to get rid of spent compost, (25p a bag). Don't muck if you want to grow roots care with the Mushroom as it tends to be limey. Seaweed is great. If you know someone who is seriously into home brew or a micro brewery the spent mash is good! You will usually find a plot that has been left fallow (unused) gives good returns the first year but the trick is to keep up the fertility. Grass etc dies down in situ and feeds the soil, we take the goodness away to feed us!
;D