Soil improvement of raised beds
I am considering constructing raised beds for my father (78 years old) who has grown veg etc in his garden for many, many years. Over this time I have seen his crop of vegetables get less and less (some not even growing) due to all the nutrients being used up in the soil. What I would like to ask is how best to fill these raised beds with soil that will feed the growing plants. Do I use the existing soil and mix in some form of horse manure. If so, how do I go about mixing in e.g. how much, and what time of year. If I cannot get horse manure what other options do I have, and again how and when would I use them. I assume what ever I use to help improve the soil has to be then done every year. If I can't get manure my concern is that improving the soil will be costly. Any advise you may be able to give would be greatly appreciated, as I would like my father to continue to enjoy his garden.