Young potato plant leaves yellowing at base

Question

I'm growing potatoes in a 5 gallon bucket. The mature leaves are a beautiful dark green, as you can see in the below photo, and the plant is growing fine, but occasionally the young, small leaves growing off the tip of the stem will start yellowing. You also get a bit of yellowing at the base of a middle-sized leaf. The yellowing has come and gone once or twice over the lifetime of the plant but I have not figured out what factor is causing it. What could be the cause?

I put the tubers in the soil around 11 weeks ago and it has not flowered, although I believe this variety is not expected to flower. The bucket has ~10 holes drilled at the bottom, maybe an 1/8th of an inch in diameter each.

Answer 1

I think that this hints for a nutrient deficiency. The yellowing of young leaves with the veins remaining green almost certainly means iron deficiency: it affects young leaves the most, because iron is an immobile element i.e. the plant can't withdraw it from the old leaves and pump it to the new ones (like it can with nitrogen for instance). A general rule of thumb is to water it with a fertilizing solution containing chelated iron (careful about the clothes, the stains it causes are VERY hard to remove!), but it's also possible that the soil's pH is way too high (which reduces the plant's ability to absorb iron), so watering it every now and then with an acidifying solution (ideally made from nitric or sulfuric acid) might help correct the imbalance faster. A foliar spray of a chelated iron solution might help as well (and usually makes for a fast and somewhat spectacular recovery), but its effects are short-lived and is not a permanent solution.