I think there is a way a person could rig up narrow raised beds so that weeding and harvesting could be done but you would have to tweak it a bit to fine tune it to your limits. The hardest part would be determining which crop to grow - which one will make the most money (for me this changes every year) and be the most fun for you to grow.

You can get a lot of crop out of a limited space if you use well worked soil, weed blocking mulch (I use landscape fabric) and rotate your crops a lot.

I would agree with trianglejohn and use raised beds and or landscape fabric there is also a weed block fabric you should be ble to get at your local garden center. I have heard of growing in straw bales but dont know much about it but that might work for you also. I hope you have a great growing season keep us up dated on how everything is going
Take a look at the link

Here is a link that might be useful: Straw Bales

Maybe think on the line of perennial flowers, they can all be pot grown and during the growing season up on benches. Use pre eminent weed control in each pot while potting the cut down on weeds. I belong to a private board and there are several people that are working nurseries in a wheel chair.

Have you thought about the possibilities of "tire gardening?" I'm about to try it for the first time this year simply cause my old back can't take the bending anymore! I've done some research and have been emailing a few folks that love it, especially for potatoes. I have found plenty of free tires, so the only cost will be the soil to fill them. One of the ladies that emails me suggested using sawdust with the soil and compost.

I'm excited and looking forward to trying it this year. Here are a few websites that I found.

http://www.ca.uky.edu/enri/gardening.htm
http://www.thegardenhelper.com/potato.html
http://www.tirecrafting.com/03gardengrow/03gardengrow.htm

Hello,
I am working on square foot gardening for the first time this year.
It would be very easy for you to accomplish I believe and you can get Mel's book at your local library. His website is squarefootgardening.com There is also a forum right here on gardenweb all about square foot gardening.

One reason I think this will work good for you, is that Mel suggests that when you build your garden box that you also make a bottom in it. Then you can place cement blocks under them to the hight that you need. You can also build them to the width in which you can reach across without having to really stretch to reach the center.
In the book he talks about the large variety of vegetables you can grow in the beds.
Just think when he talks about trellising up you can trellis downward =)
Being in a wheelchair has nothing to do with gardening, sorry that ship just doesn't work as a negative here! Wow, your family has a nursery, I am soooo drewling over that!

Please keep us posted on how you do =)
cristi