>>57074>>57130Hey OP
I too started gardening about 5 years ago on very poor sandy soil. Though I still have a lot to learn in general, I can confidently say I successfully mended my soil (chemistry student with access to labs).
I worked my soil to a depth of about 50cm (20 inches) the first two years. I mixed in loads of 'woody' organic matter in the form of semi-composted hedge clippings and leafs to help with moisture retention. My soil, as most sandy soils, tended to dry out rather easily. I borrowed the idea from 'Hügelkultur', applied it to my beds and it worked out quite well for me.
The last few years I only worked the soil to the depth of the blade of my spade without apparent negative effects (12inches). I also started working in manure (, a mix of cow, chicken and rabbit manure to be precise,) to add more nutrients as I started growing more demanding crops. I stop adding manure to my compost heap around the start of winter so it has about 4 months to age. The manure smells (almost unnoticeable) little in the beginning, and not at all at the end of the process.
I only used artificial fertilizer to get my Mg-levels in the green. All other micro- and macronutrient levels as well as pH-values were adjusted to within an acceptable range by simply adding decent compost. I did it in the course of 3 to 4 years, but I'd like to point out I only tend to my garden about two or three weekends a month max due to severe time constraints. With a bit more dedication I'm pretty sure it can be done in 1 growing season, 2 tops.
I'll dump some photos for your amusement; OC but I've posted them on /diy/ before.