Beverley
I’ve successfully grown very large Desirees the last two years in the ground. I usually wait till near the end of April to plant and when i do, I put as many comfrey leaves in the trench as I have available, along with some BFB. I also feed with comfrey tea and/or tomorite once the plants have reached full size and have flowered. I usually harvest Desirees after 20 weeks growth, plant and feed using Maria Thun biodynamic calendar.
The crop is usually a mixture of small, medium and large but I’ve not done any studies on how to preferentially generate the large ones. What I will say is that, usually, the number of stems per seed tuber usually correlates with the yield you harvest from that individual plant. The more stems the better……
Eliot Coleman says that you get the best yields of potatoes sowing them in rotation directly after sweetcorn, but I’ve never tried that as the garden isn’t big enough to have that amount of corn!!