The usual advice with raised beds for vegetables is to make them narrow enough so you can reach the middle without standing on it - and if it's possible that you will decide to use the beds for something other than soft fruit, then your plan makes sense. However, espalier trees are not the easiest for a beginner and as most fruit is perennial (so you only plant it once, or once in ten years, perhaps) there's less need to have two narrow beds.
So my thought would be to make a bigger, central bed and plant dwarf or semi dwarf apple/pear/plum trees in the centre of the bed. So for example you could plant two apples on M26 rootstock plus 2 Quince A rootstock pears or 'Pixie' stock plum/greengages, (or have one each of the plum and pear if you choose self fertile varieties). This would require much less intricate pruning to get them productive.
Then plant fruit bushes around the perimeter so they are a good distance away from the the trees and have your path right around the outside of the beds so you can easily get to the bushes all around. Potentially you could then grow some climbing fruit - blackberries, wineberries, loganberries, even mini kiwi fruit on your fences if there's enough room to walk past without being smacked in the face by a wayward spur.
Bear in mind that some bushes - Jostaberries and Redcurrants for example - are big plants so need some elbow room.
If there isn't room to do all that and/or you're determined to go for the trained trees, I'd recommend you start with those and get them reasonably well established for a few years before you begin to introduce under-planting within a 5 feet or so radius of their roots. Once the trees are fruiting fairly well - usually 3 years or so - you can allow the raspberries, strawberries and other low growing fruit to encroach a bit closer.
Or just plant the bushes in the beds and plant the trees elsewhere. Or train the trees against the fences as you planned but planted into the ground and create a central raised bed with the bushes and other fruit.
Last edited: 11 September 2017 09:01:00