Yard & Garden News

Shining a light on why potatoes turn green

Tuesday, October 20th, 2020
Pencil near potato pointing out buds

Potato tubers turn green when exposed to light.

Whether store-bought or homegrown, potatoes will turn green when they are exposed to light. Most folks know that they shouldn’t eat potatoes that have turned green, or should at least cut away the affected portion. But it’s not actually the green color that is the problem.

The green color comes from the pigment chlorophyll, produced as a response to light. The potato tuber that we eat is actually a modified stem structure that grows underground. The “eyes” of the potato tuber are buds, which will sprout into shoots.

Potatoes will turn green when growing too close to the soil surface as well as when stored under even low-light conditions. Mulching potato plants in the garden and storing harvested potatoes in complete darkness will prevent them from greening.

Chlorophyll is not toxic. However, another response of the potato tuber to light exposure is increased production of a colorless alkaloid called solanine. The amount of solanine increases with the length of exposure and the intensity of light.

Group of potatoes

Potato tubers buds sprout into shoots.

Consuming a large quantity of solanine can cause illness or even death in extreme cases. However, most people are not likely to eat enough of the affected tissue to cause illness because of solanine’s bitter taste.

The highest concentration of solanine is in the skin of the potato; removing the green portion will also remove most of the toxin.  Sprouts of the eyes are also high in solanine and should be removed before cooking.

The next time you see a green potato, be thankful for that color change because it is warning you of the presence of toxic solanine.

Yard & Garden Calendar – November 2020

HOME (Indoor plants and activities)

As houseplant growth slows, apply less fertilizer and water.

If plants are dropping many leaves, move them closer to sunny exposures, such as west- and south-facing windows. Artificial lights may be needed to supplement particularly dark rooms.

Pot spring-flowering bulbs with tips exposed to force into bloom indoors. Moisten soil and refrigerate 10 to 13 weeks. Transfer to a cool, sunny location, and allow an additional three to four weeks for blooming.

Continue dark treatment for poinsettias by keeping them in complete darkness from 5 p.m. to 8 a.m. daily until early December or until red bracts begin to show.

YARD (Lawns, woody ornamentals and fruits)

Prevent rabbit and rodent feeding damage by erecting physical barriers, such as metal mesh (one-fourth inch) hardware cloth. Pull mulch a few inches away from the trunk, as the mulch provides a warm winter home for rodents. Chemical repellents also are available, but their effectiveness is temporary and not foolproof.

Prevent frost cracking (or sunscald) by wrapping trunks with commercial tree wrap or painting the south- and southwest-facing sides of the trunk with white latex outdoor paint. Young, thin-barked trees such as maples and many fruit trees are especially susceptible. Be sure to remove the tree wrap by early spring to prevent overheating of the bark.

Remove dead, diseased or damaged branches.

Protect the graft union on rose bushes by mounding soil around the plants and adding mulch on top. Wait until several killing frosts have occurred so plants will be dormant when covered. Plants covered too early may be smothered.

If you are planning to order a “live” Christmas tree, prepare its planting hole before the soil freezes. Mulch the area heavily to prevent freezing, or dig the hole and put fill in a protected, nonfreezing area such as a garage or basement.

Clean up and discard fallen leaves and fruits around fruit plants to reduce disease carryover.

Continue mowing lawn as needed. As tree leaves fall, run them through your mower (remove bagger), allowing the shredded leaves to remain on the lawn. Be sure to mow only when grass and leaves are dry.

A November application of fertilizer can help keep lawns green into winter and boost early spring recovery. Apply one-half to 1 pound actual nitrogen, per 1,000 square feet of lawn. See “Turfgrass Management: Fertilizing Established Cool-Season Lawns” for more information on lawn fertilization.

GARDEN (Flowers, vegetables and small fruits)

If frost hasn’t taken your garden yet, continue harvesting.

Harvest mature green tomatoes before frost, and ripen indoors in the dark. Store at 55-70 degrees F. The warmer the temperature, the faster they ripen.

Harvest root crops and store in a cold (32 degrees F), humid location. Use perforated plastic bags as an easy way to increase humidity.

Remove crop and weed plant debris from the garden and add to the compost pile. This will help reduce the carryover of diseases, insects and weeds to next year’s garden. See Managing Yard Wastes: Clippings and Compost for more information on composting.

Fall tilling, except in erosion-prone areas, helps improve soil structure and usually leads to soils warming and drying faster in the spring. This allows crops to be planted earlier.

Apply mulch to strawberries to prevent winter injury or death to their crowns. Wait until temperatures have hit 20 degrees F to be sure plants are dormant. If mulch is applied too soon the plant’s crown can rot.

Dig and store tender flowering bulbs, and keep in a protected location.

Complete planting of spring-flowering bulbs.

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Author: B. Rosie Lerner, rosie@purdue.edu
Editor: Charles Wineland, cwinelan@purdue.edu
Category: Extension, Horticulture & Landscape Architecture
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