The growth of a potato can be broken down into five stages.

The table above has been reproduced with permission from Johnson, D. A., ed., 2008, Potato
Health Management, 2nd ed., American Phytopathological Society, St. Paul, MN.

Growth Stage I: Sprout Development
The first stage begins with sprouts developing from the eyes and ends at emergence from the soil.  The eyes of a potato are the little black spots that appear on the skin of the potato.  The stems of the potato sprout from the eyes.  The seed piece or seed tuber is the only energy source for growth during this stage.

Growth Stage II: Vegetative Growth
The second stage is the stage in which all vegetative parts of the plants (leaves, branches, roots, and stolons) are formed. It begins at emergence and lasts until tubers start to develop. Growth stages I and II last from 30 to 70 days depending on planting date, soil temperature, climate, and other environmental factors.  Potatoes grown in Region 3 like Chegutu-Kadoma area, for instance, don’t have a long growing season, so the first two stages can’t take 70 days or the plants would never produce any tubers.

Growth Stage III: Tuber Set/Initiation
During the third stage of growth, tubers are forming at stolon tips, but are not yet enlarging. If you were to dig up a potato plant, the tubers would be about the size of a jelly bean and would loo like a mini potato.   This stage lasts about two weeks depending on location, planting date, climate, soil type, and variety. Tubers form when the plant produces more carbohydrates than are required for vine growth. Varying weather and moisture conditions cause uneven tuber set and growth. The number of tubers formed per plant is called the tuber set. The plant may initially produce 20 to 30 small tubers, but only 5 to 25 tubers depending on tuber size under cultivation typically reach the medium to large size both comprising the commercial grade, 25 being an extremely high case.

The growing plant absorbs some of the tubers in the original set. The number of tubers that achieve maturity is related to available moisture and nutrition. Optimum moisture and nutrient levels early in the growing season are critical to the maintenance and development of tubers.

Because water levels are so important, farmers will irrigate their fields on a daily basis and sometimes more if needed.  This is why you may see irrigation systems running at night, as well as during the day.  Different farmers have different strategies about irrigating fields. When a field is irrigated during the day, the potato plants are cooled and the leaves are less susceptible to heat damage.  However, some of the water evaporates because it is so hot out, so the farmer has to put more water on the field.  Irrigating at night makes sure most of the water is absorbed by the plant, but it doesn’t cool off the plant during the day.  So many choices!

Growth Stage IV: Tuber Bulking
Tuber cells expand with the accumulation of water, nutrients and carbohydrates. Tuber bulking is the growth stage of longest duration. Depending on date of planting and other factors, bulking can last up to three months, but it usually lasts about 45-60 days.

Growth Stage V: Maturation
Vines/ haulms turn yellow and lose leaves, photosynthesis gradually decreases, tuber growth rate slows and the vines die. This stage may not occur when growing a long season variety like Panamera or Valour (the potatoes you most commonly used for baked potatoes) in a production area with a short growing season like those found in Region 3 which are characterised by high temperatures. In that case, the plant ‘s growth rate is slowed by growth regulants like Supress or Cultar both the active ingredient for each being Paclobutrazol before harvest.  The vines are also killed to minimize the work the farm equipment has to do in the field. Some other varieties like Tyson and Sifra being short growers, however, will complete this stage and there will be almost nothing left of the plant but decayed stems and leaves when it is time to harvest the potatoes. Peeled potatoes, on the other hand, are cut short of their maturation period because consumers like eating the small potatoes and farmers can’t sell their peeledred potatoes if they get too large.