Potato Growth Pattern

The growth of a Potato plant can be divided into four distinct stages.

1) Vegetative stage For the first 30 to 70 days the plant produces main shoots and lots of foliage. The larger the plant at the end of this stage, the larger the eventual yield can be. Watch out for pests such as Colorado Potato Beetle during this stage. Vegetative growth goes along best during the long days of early summer.

2) Tuber formation After 70 to 90 days of vegetative growth the main shoots stop growing and side branching occurs. At this time tubers start to form on stolons coming from the feeder roots. A temperature of 60 to 65˚ F is said to be optimal for tuber formation and it slows down at temperatures above 70˚ F. This stage usually coincides with the onset of flowering and is a good indicator that tuber formation has begun. It is not physiologically related however and in some situations flowers may not appear at all.

3) Tuber enlargement As the plants come into full bloom the tubers enlarge rapidly and the plant has its greatest need for potassium. This is also the most critical time for water and for maximum growth they need a steady supply. You can start digging new potatoes at this stage. Fungus diseases often attack plants at this time.

4) Maturation When the plants reach maturity the tops wither and die back and the skins on the tubers thicken (this is important for storage). When 75% of the foliage is dead, water them for the last time, wait 10 to 14 days and they are ready to dig.

Certified disease free tubers

You can grow perfectly good potatoes using old potatoes from the market (supposedly they are often sprayed to prevent them sprouting but they do sprout eventually). The problem is that these may be infected with virus diseases, which will then become established in your garden. Once a virus is established in your garden it is there to stay and can infect every subsequent crop (and maybe even Tomatoes, Peppers and Eggplants as well). Because of this problem most authorities recommend planting only certified disease free tubers. Its hard to get optimal yields from poor quality seed Potatoes, no matter how good your soil and cultural practices.

Selecting seed potatoes

A tuber is not a root, it is a swollen stem adapted to be a food storage organ and has a small scar on one end where it was attached to the plant by the stolon. The other end of the tuber (the rose end) has a cluster of dormant buds known as eyes, which have the ability to grow into new plants. There are also eyes in other parts of the tuber and you can cut one tuber into several pieces. You just have to make sure that each piece has an eye that can grow (even a Potato peeling can grow if it has an eye). However the rose end contains the most vigorous shoots.

There is much debate over the ideal size of a seed potato (this is the kind of thing that makes gardening so exciting), but it is smaller than many people think. Most books recommend 2˝ to 4˝ (3 to 4 ounces) tubers, saying smaller ones produce smaller plants and hence smaller tubers and lower yields. They say that larger tubers produce bigger plants and hence larger tubers.

Agricultural researchers in England obtained their highest yields by planting very small (1/3 oz) tubers very close together (only 9˝ apart). They found that larger tubers (spaced further apart) sent up several shoots that essentially became separate plants and eventually competed with each other. Using smaller tubers can also reduce seed potato costs significantly.

Of course many gardeners get the same results by cutting larger tubers into several pieces, each with 2 to 3 eyes, but cut pieces are much more prone to rot. To minimize this they should be left for a few days, so their cut surfaces can dry out and toughen. They can also be dusted with sulphur and left for 24 hours. These measures usually work out okay, but you may as well just use smaller tubers in the first place.

Sets: If you buy seed Potatoes by mail order they may very well be in the form of sets. These consist of a single eye from a tuber with a small plug of potato attached. This is not a very satisfactory way to grow potatoes. Even if you are fortunate enough to get sets in good shape (which is not always the case), they won’t perform as well as whole tubers with their large reservoir of food to draw from. They may also be coated with fungicide for interstate shipment.