For years I would purchase seed potatoes from the mainland, assuming that since they were certified to be disease free that they actually were. But recently while investigating some USDA standards I came upon a document governing seed potato certification. To my disappointment I learned that fields with late blight and other problems will still be certified as disease free as long as the percentage is low. My, but that's not good enough for me. I come from a veterinary background, so that would be like saying it was ok for me to allow 1% of patients to deliberately die without taking any steps. Since the practice about 10,000 patients, that means I could kill 100 dogs and cats a year and it would still be acceptable. No way! No way!
So I am switching to growing my own seed, especially potatoes and sweet potatoes.
My seed production area will be kept apart from the food production garden. This way I can carefully screen each individual plant, eliminating slow growers and less vigorous plants. When it comes to culling, I can be ruthless. As you can see in the photo below, I've already pulled out the less robust plants.
Each row of plants is labelled. You can see the very visible yellow labels. I alternate varieties so that I don't accidentally mix things up. So a row of purples would be next to a white, next to a red skinned, next to a small fingerling, etc. Since I grow quite a variety it's no trouble alternately the color and types.
Once the plants are growing well, I begin to mulch them. Initially the mulch is only two inches deep. But eventually I will apply mulch two more times making it 6-8 inches deep. Those 2x4 wood pieces in the photo below are 7 inches long, just to give you some perspective.Deep mulching works really well on potatoes. It not only keeps weeds out. More importantly it keeps soil moisture levels fairly constant and it keeps light away from the tubers.
I've just harvested my first few varieties that are early types. It took just two months from the time they were planted to the time of harvest. Here in Hawaii the potato plants don't die back to indicate harvest time. Instead they look "old" and ratty. A variety called Dark Red Norland proved to be the fastest producer with Red Thumb right behind it. Guess the weather was just perfect for them this year.