Thank you for your inquiry about putting your potato plant outside now, will the growth of the potato plant be effected if the leaves are killed by a spring frost.  If your potato leaves are exposed to freezing temperatures, the leaves could be killed or damaged.  If the growing tip is killed and the damage is not severe, the buds lower on the stem could sprout. How soon the plant can resume growth will depend on the severity of the damage. If the damage is severe and the entire top of the plant is killed, there are different opinions about whether the plant could die, the crop could be reduced or if the plant could sprout from a tuber. It probably depends on the health and age of the plant. Potatoes need photosynthesis to take place in the leaves in order to form the potatoes.  Your plants are growing in a bag and may not have the benefit that the warmth in the ground can provide, not be hardened, have more susceptibility to the cold, and have an increased possibility of frost damage.  If possible, the best way to protect your plant would be to move it back into the garage when a frost threatens.  More about hardening follows below.

Colorado State University Extension GardenNotes  # 719, Vegetable Hints, suggests that for vigorous growth, the soil temperature should rise above 50 degrees before potatoes are planted. It may be too soon for your potatoes to be outside overnight. You can check the temperature of the soil in your bag. Please see the link below.

http://cmg.colostate.edu/Gardennotes/719.pdf

Your potato plant should be hardened before being place outside in a permanent location after the danger of frost is past. The plant may have been growing in a sheltered location with constant warmth to the roots, indoor lighting, and no exposure to the sun, wind, moisture and temperature fluctuations that takes place outside.  Plants that are placed outside from an indoor/greenhouse environment can experience sunscald from the stronger light and also desiccation caused by water being lost from the leaves. It is very important that your plant develops a thicker cuticle, waxy coating on the leaves, which can protect the leaves from environmental stresses, this is called hardening off.  This process takes about 7-10 days and involves exposing the plant gradually to an increase in sunlight, and wind. A shady, non-windy location for an hour or two could be a good starting point. It is advisable to monitor the plant carefully for sunscald and wilting. Larger plants can take longer to harden.

If you wish to leave the plant outside, the following Colorado State University Extension GardenNotes #722 provides information about the types of frosts plus ‘Frost Protection and Extending the Growing Season’. it is important to capture the heat from the ground.  Blankets and sheets, floating row covers and heat sources are discussed.

http://cmg.colostate.edu/Gardennotes/722.pdf

Light is another important issue. You had mentioned you thought the plants should be exposed to outdoor sunlight, this is correct. Outdoor crops require 4,000 to 1,200 foot candles, the more light a plant receives, the higher the photosynthetic rate will be. Please see the Colorado State University Extension Garden Notes #142 below which discusses light.

http://cmg.colostate.edu/Gardennotes/142.pdf

I have also included for you a climate summary and planting recommendations for Colorado Springs please see the link below.

http://cmg.colostate.edu/Gardennotes/743.pdf l

I wish you success with your potato project.

Barbara S.

El Paso County Colorado Master Gardener