Potassium in Potatoes: Vital to all Growth Stages.

A potato has five growth stages: sprout development, vegetative, tuber initiation, tuber bulking and maturation. Potassium (K) plays an essential role throughout all five stages ― promoting root development, activating over 80 plant enzymes, synthesizing carbohydrates, increasing protein production and much more.

1) Sprout development

At a crop’s earliest start, adequate potassium supports a plant’s ability to resist disease and tolerate frost or other stresses.

2) Vegetative

The second stage is when roots, shoots, leaves and stolons form. Sufficient K2O is needed for effective root development. Potassium also supports the opening and closing of stomata—the pores in leaf surfaces involved in gas exchange and photosythensis1.

3) Tuber initiation

Tubers form when the plant produces more carbohydrates than required for vine growth. The number of tubers that achieve maturity is related to available water and nutrition2. Proper K levels help ensure strong roots for effective uptake, but a potassium source high in sodium can inhibit root function.

4) Tuber bulking

During this critical growth period, tubers expand by successfully accumulating water, nutrients and carbohydrates. Potatoes require large amounts of soil K2O at this stage because potassium is crucial to many metabolic functions, including the movement of sugars from the leaves to the tubers3.

Potassium also promotes photosynthesis, and research has shown that tuber yield can be influenced by the photosynthetic activity and duration of the leaf canopy. If nutrient deficiencies limit canopy growth, yields can suffer4.

5) Maturation

At this stage, the potato skin thickens for protection while specific gravity (dry matter) increases. Potassium is important for dry matter growth and the conversion of free sugars into potato starch5.

Potassium plays a vital role throughout all of the potato growth stages. And because of its importance, serious consideration regarding potassium source must be kept in mind. A potassium deficiency or the wrong K source can impact the yield, size, and quality of a potato crop. 

Protassium+ ® sulfate of potash (SOP) is a premium potassium source that provides an ideal combination of potassium and sulfate sulfur without the unnecessary nutrients found in alternatives. Protassium+ fertilizer contains virtually no chloride and has the lowest salt index of all major potassium sources, helping minimize the damage that salt can do to plants and soil biological systems.


1,4-5 Stark, J., Westermann, D., Hopkins, B. "Nutrient Management Guidelines for Russet Burbank Potatoes." University of Idaho Extension. Bul 840, 2009.

2 University of Wisconsin - La Crosse. "Potato Growth Stages.” Bioweb.

3 Mikkelsen, R. "Best management practices for profitable fertilization of potatoes." Better Crops with Plant Food, vol. 90(2), 2006.