Released February 23, 2009
URBANA, Ill. -- As spring weather slowly works its way up from the south, so does the heat and humidity, said a University of Illinois Extension horticulture educator.
"You know you are going to have a bad day when the thermometer and the humidity gauge both follow the clock," said Jeff Rugg. "At 7 a.m., they are both in the 70s and by 10 a.m. they have both reached 100.
"If you think you have it bad, think about your plants. They cool themselves with water evaporating off the leaves, but when the humidity is high, they can't stay cool."
Some plants grow in hot and humid jungles and aren't affected as much by the heat and humidity
Tropical locations often have high humidity because of frequent rainfall, sometimes even daily. The plants are cooled by the rainfall and have plenty of moisture available to the roots.
In the United States, hot weather is often rain free, but the humidity stays high because of weather systems that come off the oceans or the Gulf of Mexico. The Gulf humidity often moves north past the Gulf States and into the Plains States and the Midwest.
"If you have a hot and humid patio that has pots of tropical plants, you may need to add some irrigation to keep your plants healthy," he said.
Here are a few of my favorites
"Call me crazy, but I like the heat and humidity. I also like a lot of the plants that thrive in these conditions."
Annual vinca (Catharanthus roseus) is not the same plant as the vinca vine that many people use in hanging baskets or as a groundcover. It is an annual that thrives in the heat. It will bloom all summer with white, pink or rose-colored flowers. It grows a foot to eighteen inches tall. Although it is trouble free and needs occasional watering to keep it blooming, it does not do well if it gets too much water.
There are other annuals that will thrive in heat and humidity. Try Alternanthera with hot pink to purple foliage. Coleus has dozens of varieties that have gorgeous combinations of colors on the leaves. Annual salvia, euphorbia and helianthus are also good.
"I especially like summer bulbs," he said. "They almost always have pretty flowers and many have a pleasing fragrance. They are easy to take care of and have few pest problems. For hot and humid conditions, you can't beat agapanthus and crinums, which are both also deer resistant."
As many as 50, two-inch-long agapanthus flowers form a ball, are borne on one-to-four foot stalks, and come in a variety of blues and white. They form clumps of bulbs with two-foot-long green leaves that are a couple of inches wide. The name agapanthus comes from the Greek words for flower of love, but it is commonly known as the Lily of the Nile.
"Crinum X powelli is the botanical name of what may be my favorite bulb," Rugg said. "Southerners commonly call it a spider lily or rain lily. They look a lot like amaryllis. Digging up an old clump to divide them among friends may take all day.
"The bulbs are often the size of a football with leaves longer than six feet tall that tend to topple over about halfway up to form a fountain-shaped clump. Newer varieties are smaller and more refined."
The flowers are the size and shape of an Easter lily flower and come in white, pink, purple and striped varieties. They are sweetly fragrant and attract butterflies and hummingbirds. Each flower stalk can bear a dozen flowers, and each clump of bulbs can send up dozens of flower stalks, usually within a week or so after a drought-breaking rain.
The bulbs not only take the heat without blinking, they can take several freezes each winter. They can be left outside in zone six. In northern states they need to be brought in, just like a canna or a dahlia.
Crinum americanum is a native North American bulb that grows in wet soil or up to several inches deep in the water from the Everglades, around the Gulf Coast and down into South America. It has white fragrant flowers and makes a wonderful addition to any water garden. In northern climates it makes a good house plant over the winter.
"You cannot beat the fragrance of the plumeria or fangipani," he said. "It is used to make the lei necklaces that are given to visitors to Hawaii. They are not the prettiest shrubs when not in bloom and especially when the deciduous species drop their leaves, but they are worthy of growing in every warm garden or in a pot, just to smell the flowers."
For a beautiful flowering shrub or small tree that thrives in heat and humidity, you can't beat hibiscus rosa-sinensis. The flowers come in every variety of red and pink from orange to scarlet, with some whites and yellows thrown in for good measure.
"The flowers are generally wide open and flat, but newer ones come in doubles and in spider forms," he said. "Probably the most important thing to know about growing hibiscus flowers is to keep the soil damp, but not too wet. If it dries out, the flower buds tend to fall off. Small amounts of daily watering will help a lot in keeping this plant in bloom."
When one thinks of tropical plants, a common characteristic of huge leaves is often brought to mind. Few plants have bigger leaves than colocasia, also known as elephant ear; this bulb has leaves that are used as umbrellas in the tropics.
It is often sold as an annual in northern states, but the bulb can be brought in and stored over the winter. It needs plenty of water and actually grows quite well in the shallows of a water garden.
Another big-leaved plant is the banana.
"If you want to eat bananas from your plant, you will need to have it in a frost-free area for 12 to 18 months," Rugg said.
If you are looking for hot-and-humid-tolerant tropical plants to grow, try the hot and humid, Louisiana-based Stokes Tropicals catalog.
"They have bamboo, ginger, plumeria, and many other beautiful tropical flowers," he said. "They also have bananas, including the Japanese fiber banana that is hardy to minus 3 degrees Fahrenheit when planted in the ground and to minus 24 degrees if given proper mulching.
"If I could find the right piece of land, I would order every plant in the catalog. Check them out at http://www.stokestropicals.com or 866-478-2502."
Tested plants
There are a lot of reliable catalogs offering tropical plants, but whenever possible Rugg prefers to have tested plants from reliable testing facilities. For plants that need to grow in hot and humid conditions, the test location needs to be hot and humid.
"Dr. Allan Armitage has just the spot at his University of Georgia trial garden," he said. "The annual and perennial flowering plants he recommends are not just heat and humidity tolerant, he also checks them to make sure they are virus free.
"This virus check is an amazing feature that I don't think any other testing program does. He searches for unique plants that are particularly pretty and perform well in the landscape or in containers. They are promoted under the Athens Select label which gives some money back to the university."
Having done the testing for more than 10 years, you might expect there would be a large number of available plants, but only about 30 plants have made the University of Georgia's list so far.
"What these plants lack in quantity, they make up in vivid colors," he said. "You will not be at a loss for color if you chose one of these plants. Eighteen of the plants have variegated leaves and several of them also have attractive flowers. These plants don't require heat and humidity, so anyone can grow them all summer long, unless they have full shade or are in a really cool location, such as in a higher altitude region."
One plant that many deep southerners wish they could grow is the red, cut-leaved varieties of Japanese maple. It is a small tree or large shrub with ferny-looking foliage that grows in the cooler northern zones of 5 through 8. In the warmer areas, they often lose their red color early in the season.
The closest look to the northern maple is provided by the two red cut-leaved hibiscus plants called Panama Bronze and Panama Red. They grow four feet tall and wide and grow in zones 8 —11. They do not bloom very often, but have large red flowers when they do.
A two-foot-tall house plant from years ago, the flowering maple is making a comeback. The Fairy Coral Red hybrid Abutilon has salmon pink flowers and grows well in patio containers or the landscape in zones 7 —11.
Lantanas have always been good plants for full sun hot spots, and Athens Select has two that can be used in flowerbeds, containers, hanging baskets or even as a groundcover. The first is Athens Rose that has flowers that start out magenta red and fade to yellow. New Gold has bright yellow flowers held above dark green leaves.
"The Ron Deal verbena is the real deal," said Rugg. "It has fragrant rose-purple flowers and can be used in hanging baskets, containers to spill over the edge, and as a groundcover."
To find more information on the whole plant list from Athens Select and where you can buy them locally, check out the web site at: http://www.athensselect.com.
Misting and irrigating
"Just about everyone has the potential to grow tropical plants if you can do a couple of things to your landscape," he said. "First, to make it more livable for you and your family, you might want to try adding a misting system or an automated irrigation system for the plants. "Check with your local licensed irrigation installer to see about adding the mist. Water is an amazing substance. Liquid water sprayed on the concrete patio will take a lot of the heat out of the concrete just to change into a gaseous form at the same temperature and then it evaporates away taking the heat with it."
Spraying a mist into the air and letting it evaporate from liquid drops into water vapor will take the heat out of the air. A misting system that is on a timer can keep your patio cool enough for your plants and for you to use during the day and evening. Even just using it manually just before you use the patio will help a lot. The mister uses very little water and cooler plants will need less water for irrigation, so there is a water savings there.
Another thing you can do for the plants is to automate the watering system for them.
"Many people don't realize that individual flower pots and hanging baskets can be watered with small tubing on an automatic system" said Rugg. "In fact, many of these plants were watered that way in the greenhouses they were propagated in.
"There are do-it-yourself kits available that hook up to a timer and the garden hoses or they can be connected to the irrigation system. Using an automated system will cut back on the labor of watering, get water to the plants at the proper time, which keeps the plants healthy and blooming and uses less water."
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http://www.aces.uiuc.edu/news/stories/news4675.html
Contacts: Jeff Rugg, (630) 553-5823
Bob Sampson, (217) 244-0225; rsampson@uiuc.edu
