The growth of a potato plant can be broken down into five stages: 1) Sprout Development - The eyes of the potato sprout and emerge from the soil, using energy stored in the seed potato. 2) Vegetative Growth - Leaves, stems, roots and stolons develop as the plant grows above ground. 3) Tuber Set/Initiation - Small tubers form at the ends of stolons, around the size of jelly beans. 4) Tuber Bulking - Tuber cells expand and accumulate water, nutrients and carbohydrates as tubers enlarge greatly in size. 5) Maturation - Vines die back as photosynthesis decreases and tuber growth

1. Growth Stages
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 Wisconsin, for instance, don’t have

2. 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
look like a mini potato. This stage lasts about two weeks. This occurs between early and late
June 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 15 tubers typically reach maturity, 15 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

3. 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 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
Russet Burbank (the potatoes you most commonly used for baked potatoes) in a production area
with a short growing season like Wisconsin. In that case, the plant is killed using an herbicide s
o the tuber can grow a little bigger before harvest. The
fields are also killed to minimize the work the farm equipment has to do in the field.
Some other varieties like Goldrush and Norkota, 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.
Red potatoes, on the other hand, are cut short of their maturation period because consumers
like eating the small red potatoes and farmers can’t sell their red potatoes if they get too large.