Daniel Gill, Merrill, Thomas A. | 1/31/2006 3:06:18 AM
By Dan Gill
LSU AgCenter Horticulturist
February weather often includes heavy and frequent rain, and this should remind us that Louisiana has a relatively wet climate.
Periods of drought certainly do occur in here, especially during the hot months of summer. But it is important for gardeners to realize that plant selection and the gardening techniques we use are largely influenced by the generous amount of rain we get during other parts of the year.
Periods of rain saturate the soil with water, and it is important for the water to drain away efficiently. Other than plants adapted to bog or swamp conditions, the roots of most plants need oxygen in the soil. They can literally drown if the soil stays saturated with water for extended periods, so we often plant in beds that are raised somewhat above the surrounding soil. Beds typically are raised about 6 inches to 12 inches, which allows the water to drain from the soil faster.
Raised beds work well in handling a heavy rain event, such as when 2-3 inches (or more) fall in a single day. What is more difficult to defend against is frequent rain over an extended period. Frequent rain events do not allow the soil to drain, since every time the water from one rain drains away another rainy day quickly comes along to saturate it again.
There is another danger to plants as a result of too much rain. Fungal disease organisms that attack plants and cause root rots and crown rots are far more likely to damage plants when the soil stays wet. This occurs partly because a plant’s roots are in a weakened state if they are deprived of the oxygen they need, but these fungi also prefer and are more active in a soil high in moisture. So plants growing in beds saturated with water for extended periods are prone to root and crown rots, which can be disastrous since these diseases often are fatal.
Fortunately, excessive rain in February is not so dire. Many plants are still dormant, which makes them more forgiving of the saturated soils. Roots are not as active and will better tolerate the reduced oxygen levels. In addition, the fungal organisms that are responsible for root and crown rots are not nearly as active when the soil is cool. So despite the frequent rains and wet soils, we generally do not see major problems in February.
If we were in July and seeing rains lead to saturated soils, the situation would be quite different. Root rots are common when rainy weather occurs during the hot months of June, July, August and early September – and at that time of year, they can be devastating.
Despite the good news about February, however, there are some negative effects we might see in various plants this time of year if wetter conditions exist.
First, the flowers of cool-season bedding plants that produce relatively large flowers, such as pansies and petunias, really get hammered by the rain. Pinch or cut off these damaged, unattractive flowers, if possible. These plants will recover when the weather becomes drier. It also is possible to see some rot occurring in cool-season bedding plants, since they are in active growth now. But that isn’t typical.
Caladiums are tropical plants that thrive in shady beds during our hot, humid, rainy summers. Since our soil never freezes, we have the option of leaving caladium tubes in the ground over the winter. But we don’t always get away with this – particularly if wet conditions persist this time of year.
Although caladiums enjoy abundant moisture when they are in active growth, they prefer to be dry when they are dormant. (Their ancestors evolved to have a dormant period that would let them survive the dry season in their native Brazilian habitat.) Exceptionally wet winter weather, such as we may experience in February, can cause the tubers to rot. This is why even though we can leave caladium tubers in the ground over winter, it generally is more reliable to dig them in fall and store the tubers indoors over the winter. If you left your caladium tubers in the ground and they don’t show up by the end of May, you will know why.
Typical wet February weather also should remind us to be cautious about using plants native to dry climates – unless they have a proven track record in our area. A number of years ago (notably in 1999, 2000 and 2002) Louisiana was experiencing unusually dry summers. As dry summer followed dry summer, interest in landscaping with plants that grow in dry climates was high. As I told gardeners that asked me about this back then, never forget that we garden in a Gulf Coast climate that is warm and humid and that, on average, we get plenty of rain. Even in a relatively dry year, one major rain event from a hurricane in August can kill off dry-climate plants.
Because we tend to get abundant rain, never forget to consider drainage when designing beds and choosing plants. Raised beds generally are the best way to ensure good drainage. If you have a low area that tends to stay wet and you don’t want to put in a raised bed, you can landscape the area with plants that enjoy wet soils. It often is better to choose plants adapted to the drainage in an area than to try and radically change it.
Even with good drainage you must choose plants that are adapted to the amount of rainfall we get. If you read a plant description that indicates a plant prefers to be dry in winter, it will have difficulty thriving in our climate. Although we may have relatively dry summers on occasion, you can pretty much rest assured we generally will have abundant rain during our winter months.
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.