Get It Growing: Evaluate Landscape Plantings Now; It May Be Too Hot To Do Much Else

Daniel Gill, Merrill, Thomas A.  |  7/28/2006 9:49:19 PM

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Get It Growing News For 08/11/06

By Dan Gill
LSU AgCenter Horticulturist

I was recently asked what should be done in the garden in August, and I replied, "As little as possible!"

Seriously, though, there is at least one important task you can perform, and that’s evaluating how well your plants are doing.

The period from late June to mid-September is the most stressful time of the year for gardeners and their plants. Indeed, our hot summer season essentially defines what trees, shrubs, ground covers and perennials we can grow successfully in our landscapes.

When you walk outside this time of the year the heat and humidity are almost unbearable. At times you can hardly breathe. If you think it’s unbearable for you, imagine what it’s like for the plants in your landscape. They can’t just go inside and cool off. Plants have to be there and take the heat day after day, night after night.

It’s enough to make you wonder how anything survives. So this truly is the time of the year when we can clearly see which plants are well adapted to our area and which won’t make it.

Other than tropical plants (which we all know have problems with freezing temperatures), it is often the late summer heat rather than the cold of winter that takes its toll on plants here in Louisiana. If daytime highs in the mid- to upper 90s weren’t bad enough (and they certainly are a problem), it is the nighttime temperatures in the mid- to upper 70s that also give plants a particularly hard time.

Although plants don’t actually sleep, lower nighttime temperatures allow their metabolisms to slow down – allowing them to kind of catch their breath, so to speak. When night temperatures stay high, a plant’s metabolic rate also tends to stay high, which means the plant is burning energy and using up food it has created.

Tropical plants are well adapted to this situation, and for them it is not a problem. But plants from cooler climates rely on the cooler nights, and if nights stay warm, those plants become weak because they use up their food too fast. But let me make it clear. The food I’m referring to is the food created by the plant for itself through photosynthesis, not fertilizer.

Add to this situation high humidity and frequent rain showers, and you have the ideal conditions for weakened and stressed plants to be attacked by a variety of insects and diseases – particularly crown and root rots that often are fatal. This intense environmental and pest pressure means only those plants that are well adapted to our summer conditions stand a good chance of surviving and thriving in Louisiana.

Many attractive and useful plants that are considered reliable, and even easy to grow, in other parts of the country will not thrive here. When we choose hardy trees, shrubs, ground covers, lawn grasses and perennials for our landscapes, we must primarily keep in mind the temperatures they will be subjected to during summer in this area.

It doesn’t impress me in the least to read that a plant is hardy down to minus 10 degrees F. It doesn’t get that cold here. Show me something that tolerates hot, humid days and sultry nights. If plants can’t take the summer heat, they are questionable for use here.

So now, when we’re sweating out of our hottest days, would be a good time to walk around your landscape with a critical eye on how things are going. Even tried-and-true plants – those that generally are reliable here – may not look their best this time of the year, so don’t be too critical. But, in particular, look at any new or unusual plants you are trying out. Which ones have collapsed? Which ones look scorched and unhappy?

Plant selection, then, is very important to a successful garden or landscape. But in the information age of magazines, books, television and the Internet, you will be exposed both to plants that will do well here and those that won’t. How do you know which is which?

As much as gardeners like to try new things, finding good plants primarily by trial and error is both frustrating and expensive. Make sure you check with local sources, such as gardening books and magazines for our state, staff members at local nurseries and friends knowledgeable about gardening here.

Your parish LSU AgCenter Extension office is an especially valuable source for local information and gardening pamphlets. You also can check out the LSU AgCenter’s Web site at www.lsuagcenter.com.

When selecting books, look for those that have the words South, southern or Louisiana in their titles. Even South in the title is no guarantee when you realize what a large geographic area the South is. "The Southern Living Garden Book" from Oxmoor House takes this into account, and that makes it very useful. Each plant is rated on how suitable it is for the Upper South, Middle South, Lower South, Coastal South or Tropical South.

Other books to help you select well adapted plants for our area include "Southern Plants" by Odenwald and Turner from Claitor’s Publishing; "Gardening in the Humid South," by Ed O’Rourke and Leon Standifer, LSU Press; "The New Orleans Garden," by Charlotte Seidenberg, University Press of Mississippi; "Louisiana Gardener’s Guide," by Dan Gill and Joe White, Cool Springs Press; and "Month-by-Month Gardening in Louisiana," by Dan Gill, Cool Springs Press.

When it’s this hot, sometimes the best thing to do is relax inside where it is air-conditioned. Read a good gardening book, look out the windows and enjoy the view, and dream about cooler weather.

Get It Growing is a weekly feature on home lawn and garden topics prepared by experts in the LSU AgCenter. For more information on such topics, contact your parish LSU AgCenter Extension office or visit our Web site at www.lsuagcenter.com. A wide range of publications and a variety of other resources are available.

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Contact: Dan Gill at (225) 578-2222 or dgill@agcenter.lsu.edu
Editor: Tom Merrill at (225) 578-2263 or tmerrill@agcenter.lsu.edu

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