Home gardeners who know nothing about horticulture are often amazed to discover that everyday potatoes and sweet potatoes not only taste different, but come from different families – even though they have a common “surname” (potato).
Solanum tuberosum is a potato that the Irish, more than any other nationality, have produced for centuries, which is why it is frequently referred to as the Irish potato. This is ironic since Solanumtuberosum in fact originated in South America, in Bolivia and Peru.
Also known as the white potato, Solanum tuberosumwas originally introduced to Ireland as a garden vegetable intended for the gentry. But during the 18thcentury it became a really important staple food for the poor. In the early 19th century it was also used as a fodder crop for cattle and other livestock.
In those early days, there were only two known diseases that affected white or Irish potato was susceptible to, dry rot and a virus known as curl. Blight, brought on by a fungus, Phytophthora infestans, first showed up in Ireland in 1728, and from then until the mid 19th century, potato crops failed time and time again. But it was between 1845 and 1849 that things got really bad, with about one million people dying during what is now known as the Irish Potato Famine – compounded the Irish potato name.
Early blight is now a major potato disease problem worldwide, particularly in hot-climate countries. Late blight is also a big problem, although it occurs in cool, wet conditions.
We now know that wind and rain carries the spores of late blight disease, which is why it is so important to plant into the direction of the prevailing wind, particularly if you are staggering your potato plantings. If late blight develops and is left unchecked it is likely to kill the plant within a couple of weeks.
Sweet potatoes, Ipomeabatatas, also owe their origins to South America, but are related to the well-known garden creeper, Morning Glory, whereas Solanum tuberosumbelongs to the nightshade group of plants.
White potatoes are tubers, while sweet potatoes are swollen storage roots. A major difference between the two is that tubers grow from eyes or buds that form from within the potato. If you slice off a piece of potato where an eye has formed, and plant it, a plant will grow from the eye.
Even though “white potatoes” most commonly have flesh that is an off-white colour and a light brown skin, relatively newcultivars with yellow, blue and red flesh are also grown. Skin colours also vary. Sweet potatoes also come with different skin colours, some of which have such intensity they are used to manufacture dyes. The flesh colour also varies, depending on the cultivar, and ranges from a light creamy colour similar to that of common white potatoes to orange.