Raised garden beds help drainage and keep plant roots from drowning in heavy rains. (Photo by Dan Gill, LSU AgCenter)

By Dan Gill
LSU AgCenter Horticulturist

(02/12/16) 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 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 annual rainfall we receive in Louisiana.

Periods of rain saturate the soil with water, and for most plants it is important for the water to drain away efficiently. Other than plants adapted to boggy or swamp conditions, plant roots 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 are typically raised about 6 to 12 inches, which allows the water to drain from them more quickly.

Raised beds work well in handling a heavy rain, such as when 2 or 3 inches or more fall in a single day. What is more difficult to defend against is frequent rain over an extended period. Frequent rains do not allow the soil to drain completely every time the water from one rain drains away because another rainy day quickly comes along to saturate the soil again.

Too much rain causes another danger to plants. 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 weakened 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 because these diseases are often fatal.

Fortunately, excessive rain in February is not so dire. Many plants are still dormant, which makes them more forgiving of 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.

If this were July, 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 can be devastating. There are, however, some negative effects we might see in some plants as a result of rains now.

First, the flowers of cool-season bedding plants that produce relatively large flowers, such as pansies and petunias, may really get hammered by rain. Pinch or cut off any damaged, unattractive flowers if possible. These plants will recover when the weather becomes drier. It also is possible to see some rot occurring to cool-season bedding plants because they are in active growth now. But it isn’t typical.

Caladiums cause special concern

Caladiums are tropical plants that thrive in shady beds during our hot, humid, rainy summers. Because our soil never freezes, we have the option of leaving caladium tubers in the ground over the winter. However, we can’t always get away with this.

Although caladiums enjoy abundant moisture when they are in active growth, they prefer to be dry when they are dormant. (Their ancestors evolved a dormant period to 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 is generally more reliable to dig them in fall and store the tubers indoors. If you left your caladium tubers in the ground and they don’t show up by the end of May, you will know why.

Plants for dry climates

Typical wet February weather should also remind us to be cautious about using plants native to dry climates unless they have a proven track record in our area. It’s true that we do have periods of drought during most summers. For that reason, I often encounter gardeners who are interested in landscaping with plants that grow in dry areas, like the southwestern United States. But I always remind these gardeners that we garden in a warm, humid Gulf Coast climate, and on average we get plenty of rain. Even in a relatively dry year, one major rain from a tropical storm or 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 are generally 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 is often better to choose plants adapted to the drainage in an area rather than to try to 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 that we will generally have abundant rain during our winter months.

Rick Bogren