The surprise potatoes

One of the potato plants I found in my garden. Two shoots and plenty of roots are growing from the tuber. Growing from the stems are several long white structures called stolens from which new tubers will grow later in the year.

A few weeks ago, I found some potato plants growing in the garden of my new home. The plants were completely surrounded by weeds but—after I nearly stabbed one with a garden fork—I realized what they must be when I noticed that the stems were growing from buried potatoes. Apparently, the previous occupants missed some of their crop when they harvested their potatoes last year.

Potato (Solanum tuberosum) is the world’s fourth most important food crop (behind rice, maize and wheat) and is grown across the globe in areas with temperate and sub-tropical climates. It belongs to the nightshade family of flowering plants, which also includes other crop species such as tomato, aubergine (also called eggplant) and chilli pepper (1).

Potatoes produce flowers that are either white, pink, red purple or blue, depending on the variety. These flowers can go on to produce small green fruits that look a bit like cherry tomatoes and each contain about 300 seeds (2). However, these fruits—like most of the rest of the plant—are poisonous because they contain the toxin solanine and several other glycoalkaloids.

The part of the plant that we call “a potato” is a structure known as a tuber, which is produced from the stems of the plant to store starch and other nutrients underground. The tubers of cultivated potatoes are safe to eat because they contain very little solanine compared to the rest of the plant. Solanine levels increase if the potatoes start to turn green, which can happen in response to light exposure, physical damage and as the tubers age (2).

The tubers allow potato plants to survive for several years (known as perennial). At the end of the growing season, the stems die back leaving just the tubers in the soil, which can produce new stems the next year. Since each individual tuber is able to produce a fully independent plant that can produce many more tubers, over successive years a single potato plant can effectively produce an army of clones. We exploit this ability in agriculture and most of the potatoes we eat are grown from tubers.

Finding the potato plants in my garden presented me with a bit of a dilemma: I was reluctant to throw them away, but I had no idea how to care for them. Aided by some advice from friends I decided to move the plants to “potato bags” (plastic bag designed for growing potatoes in that you fill with compost). This freed up the vegetable patch for the vegetables I had originally planned to grow and should make it easier for me to harvest the new tubers at the end of the season.

The potatoes survived their move and are now thriving in the bags.

Some of my new neighbours spotted my potato bags and I told them about how I had found the plants. They have an allotment and—concerned that my surprise plants may not produce many potatoes—they popped around a few days later to give me a few of their own seed potatoes (Thank you!). Seed potatoes are tubers that are grown with the intention of using them to grow potatoes as opposed to being eaten. They are carefully grown and regularly monitored to be sure that they are disease free. In the UK, most seed potatoes are grown in Scotland where the cold winters kill pests and the wind deters aphids from attacking the plants and spreading plant viruses.

So, I now have two small sets of potato plants to care for over the summer and into autumn. When the foliage starts to turn yellow they will be ready to harvest, and hopefully I will have some tasty homegrown potatoes to eat this winter.

Potato is the Organism of the Month on Plant Scientist. To see the organisms featured in previous months click here.

References:

1. Kew: Solanum tuberosum (potato) http://www.kew.org/science-conservation/plants-fungi/solanum-tuberosum-potato (retrieved 03/06/15)

2. Wikipedia: potato http://en.wikipedia.org/wiki/Potato (retrieved 03/06/15)