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Ask the ISU Experts

Watering Trees for Winter

Note to media editors: Got gardening questions? Call the Hortline at (515) 294-3108, Monday-Friday from 10 a.m. to noon and 1 to 4:30 p.m., or e-mail us at hortline@iastate.edu. For more gardening information, visit us at Yard and Garden Online, http://www.yardandgarden.extension.iastate.edu


Are sweet potatoes and yams the same thing? 

In the United States, sweet potatoes are often referred to as “yams.” However, sweet potatoes and yams are different crops. 

Sweet potatoes (Ipomoea batatas) are vining plants in the morning glory family. They are believed to be native to Central and South America. The storage roots of sweet potatoes are short, blocky, with tapered ends. They have a smooth, thin skin. There are two main types of sweet potato. Dry-fleshed types usually have a light yellow skin and pale yellow flesh. When cooked, they are dry and crumbly, much like a baking potato. Moist-fleshed types typically have a dark orange skin, orange flesh, and are moist and sweet when cooked.  In the United States, the moist, orange-fleshed types are the most commonly grown sweet potato and are often referred to as “yams.” 

True yams (Dioscorea batatas) are vining plants in the yam family. They are native to Africa and Asia. Yams are long, cylindrical, underground tubers with a rough, scaly skin. Tubers can be several feet long and weigh 50 pounds or more. Yams are rarely found in the United States. However, they are popular in Latin American countries.

The word “yam” comes from the African word “nyami” (meaning “to eat”) for true yams. It is believed that black Africans brought to America during the slave trade began referring to sweet potatoes as “yams” because of their similarity to true yams.  

We have received very little precipitation this fall.  Should I be watering my trees and shrubs? 

Despite the recent dry weather, most healthy, well-established trees and shrubs are probably fine at this time. Well-established trees and shrubs have large, extensive root systems. These extensive root systems allow plants to absorb moisture even when soils are fairly dry. The dry weather poses the biggest threat to trees and shrubs planted in the past one or two years.  Because of their relatively small root systems, these recently planted materials may not be able to absorb adequate amounts of moisture before winter. Recently planted evergreens are especially vulnerable as they retain much of their foliage (needles) during winter. These needles lose considerable amounts of moisture on mild, sunny, winter days. 
Because of the dry conditions, it would be wise to water trees and shrubs planted in the last one or two years. The roots of recently planted trees and shrubs are mainly confined to the plant’s root-ball (balled and burlapped material) or root-mass (container grown plants) and the soil immediately around them. When watering these plants, slowly apply water to the root-ball or root-mass.  A thoroughly soaking about once every 10 days should be sufficient.  Watering can be discontinued when the ground freezes.  (Plant roots are unable to absorb moisture when the soil is frozen.) 

The air in our home is extremely dry in winter.  Should I mist my houseplants? 

Many houseplants prefer a relative humidity of 40 to 50 percent. Unfortunately, the humidity level in many homes during the winter months may be only 10 to 20 percent. 

Misting houseplants is generally not beneficial.  To be effective, misting would have to be done several times a day and is not very practical. 

Humidifiers are an excellent way to increase the relative humidity in the home.  There are also other ways to increase the relative humidity around houseplants.  Group the plants together.  The water evaporating from the potting soil, plus water lost through the plant foliage (transpiration), will increase the relative humidity in the vicinity of the houseplants.  Another method is to place the houseplant on a tray or saucer containing pebbles and water.  Make sure the water level does not reach the bottom of the pot.  As the water evaporates from the tray, it raises the humidity around the plant. 


Contacts :

Richard Jauron, Horticulture, (515) 294-1871, rjauron@iastate.edu

Jean McGuire, Continuing Education and Communication Services, (515) 294-7033, jmcguire@iastate.edu

A high resolution version of the above photo, suitable for printing, is available for use with this  column: [wateringtree3.jpg] 1.15 MB