Ten years ago, almost nobody was talking about indeterminate potatoes. Over the years, interest has crept up to the point where I now receive hundreds of inquiries each year about which of the varieties that I offer, or which potato varieties in general, are indeterminate. This is surprising, because it is a rather obscure topic when it comes to potatoes.
Most people are familiar with indeterminacy from their experience with tomatoes, where it is an important trait. Determinate tomatoes are generally compact and early, while indeterminate types continue to grow and flower over a long period of time. A potato plant with a determinate habit flowers at the end of each stem and then grows no larger. This is how it works in theory, anyway. Many potato varieties don’t flower much, but whether or not they actually flower makes no difference in habit. A plant with an indeterminate habit flowers on laterals, but not at the end of the stem. The stem continues to grow and produce more laterals, so the plant is able to continue growing and flowering for longer. Determinate potatoes normally top out at about two to three feet tall. Indeterminate varieties can grow stems as much as seven feet long, eventually becoming sort of sprawling vines. While a determinate variety will produce a single crop of berries, ripening over a short period of time, an indeterminate plant can still flower and form new berries when you have already harvested ripe berries from the lower laterals.
You may deduce from that description that indeterminacy works the same way in tomatoes and potatoes. That’s right. Many people start there and then draw an additional, and incorrect, conclusion: that the underground structure will mirror the above ground structure and that the plant will continue to produce additional lateral stolons with more potatoes. Unfortunately, that isn’t the case. It is easy to imagine that it would be a great thing. Wouldn’t it be nice if potatoes went on, growing more and more, if you just knew the secret for picking the right kind? It is a tempting idea, but if you think about it in a little more depth, you might wonder where the extra energy to produce those tubers would come from. After all, with tomatoes, the fruits ripen and drop off, so the plant doesn’t have to keep putting energy into them. The potatoes remain connected to the plant until harvest, continuing to grow and store more energy. That’s the catch. If your house is powered by solar panels and you plug in twice as many batteries, you just have twice as many batteries that are half filled. The situation is much the same with potatoes. The leaves are their solar panels and the tubers are their batteries. The only way to get twice as many tubers from the same amount of foliage in the same amount of time is for them to be smaller. Even if indeterminate potatoes did produce additional levels of tubers, the yield would be lower, which is not something that most people would want. I have already covered this topic from a different angle, in much more detail, in my article about potato towers.
As you can see, determinacy is not really a useful concept with potatoes, unless you are specifically concerned with flowering and berrying or the structure of the foliage. When it comes to tubers, it makes little difference. While the terms are similar in regard to the actual outcome, determinacy is rarely mentioned in the research literature and, in everyday discussion, it is overwhelmingly associated with a misunderstanding about how potatoes grow. The more useful and much more commonly used concept with potatoes is maturity. Early and mid-season potatoes are generally determinate; they grow to a certain size, flower and begin forming tubers, and then die back uniformly. Late potatoes are generally indeterminate; they keep growing until killed by frost or with herbicide, as is often done at commercial scale. Late potatoes can yield more than early or mid-season types and often produce larger tubers as well. They invest more of their initial energy in producing a larger plant. If the season is long enough, they can leverage that additional foliage to collect more energy to form more and larger tubers. This is purely a function of time though. A late variety in an appropriate climate has more time and more foliar surface area to collect energy. It is worth considering that, while a late variety can yield more, it will also take up more space. Because of that, late varieties are not necessarily the most efficient way to get more yield. If you could grow four mid-season plants in the same space as one sprawling, late variety, they will probably outproduce it.
If you see people using the terms “determinate” and “indeterminate” when discussing potato tubers, you should probably regard them as inexperienced with potatoes. Perhaps they know a lot about tomatoes and haven’t grown as many potatoes or perhaps they simply accepted information found on the Internet uncritically, as we all do at times. The best thing that we can do is try to focus on discussing potato maturity and hope that indeterminacy eventually drops out of the common potato parlance.