Managing Soil Moisture for Ornamental Plants

William Hogan  |  5/25/2011 8:43:01 PM

Not to sound like a broken record, but it has been dry. It was dry all spring and winter. With the exception of the Mississippi-Atchafalaya basins, the entire state has been severely short of soil moisture. South Louisiana is dry on both sides and drowning in the middle.

Almost every plant problem that I have seen for the past weeks has been caused by or contributed to by drought. This is true for lawns, vegetables, fruit trees, flowers, pasture, rice and soybean. Today I will discuss managing moisture in ornamental plants and vegetables. Even if it rains before this is published (and I hope it does), it’s still applicable. We have a moisture shortage of some type every summer.

Proper soil moisture maintenance seems to be the key factor for most gardeners in having successful summer ornamental plants. This is true for recently transplanted items. It is also true for established plants during the time you go on vacation. Understanding how to maintain adequate soil moisture will go a long way in assuring that your ornamentals and flowering plants remain alive and attractive throughout the hot summer season.

The most vulnerable plants to drought are those that were transplanted within the past year. For many years, I have received calls from gardeners who transplanted a shrub in the spring, watered and cared for it for the first several months, only to have it wilt and die in mid to late summer. More often than not, the plant looked prosperous and was growing well in June. The gardener went on vacation in July and returned to find the previously healthy plant dead. This condition has been called "transplant shock." What it means is that the plant had not sufficiently established a root system to support its self during a hot, dry period. This root system establishment takes longer than many people realize. I do not feel confident in plant establishment until the shrub or tree has been transplanted and growing for a period of one year. Other older plants in the garden may show no signs of distress. Their root system is better established; more in balance with the stem and leaf mass of the shrub and enables them to withstand stress. No matter how large the new plant was at planting, the successful gardener should treat it like a “baby plant” for its first year. This means providing adequate irrigation and sufficient mulching of the root zone all summer long.

Even with proper care, you will lose some transplants. We live in a part of the world that has many soil-borne fungi. Under certain environmental conditions, these fungi will attack the plant’s roots and further reduce its ability to resist stress. However, maintaining good growing conditions increases the plant’s ability to resist these root diseases. There is also variation in the ability to resist stress between individual plants and between species of ornamental plants. Some just have more vigor and adaptability. No matter how much care you provide, don’t expect to save them all. But, continuous care will increase survivability significantly.

New and established plants are both highly vulnerable to stress if they are growing in containers. Their root system is confined to this small area and the plants are more dependent on your management of this environment. How do you manage these when you are on vacation? A simple method is to ask a friend or neighbor to water the plants in your absence. Be sure to leave correct instructions regarding the needs of each species of plant. If a willing and dependable friend isn’t available, you can still manage the situation. Place all of your outdoor container plants in a group in a shady place such as under a shade tree. If a tree isn’t available, you may utilize a covered patio or near the north side of a building. Water the plants thoroughly. This method should be sufficient for an absence of a few days. If you are gone for longer, you might invest in an inexpensive irrigation timer. These are sold in garden and plant nursery stores. They are applicable to drip irrigation systems, soaker hoses or sprinklers. Sprinklers aren’t my favorite method to irrigate plants, but for a short time on grouped containers, a sprinkler might be the most practical method.

Don’t forget your indoor plants when you leave for vacation. These are not usually under the stress of heat, but they will also dry out over time. Move indoor plantings away from sunny window locations. Just before leaving, thoroughly water all your indoor plants. Plants in small pots will tend to dry more quickly. You may cover these loosely with plastic to reduce transpiration. If you go this route, be sure that these plants are out of direct sunlight. Heat can build up under the plastic and cause tissue damage.

Before you go away from home for an extended time in summer, you can place the large container outdoor plants in a small child’s wading pool under a covered patio. Put about one-half to one inch of water in the pool. As the container dries, the water is wicked into the containers through the drain holes in the bottom of the pots. Since the containers are under a cover, there is little chance of over watering due to a sudden rain storm. This method takes a little experimentation to see what works best, and you do occasionally over water a plant. But it can accomplish its purpose while you were absent during a time of drought.

Flower beds and vegetable gardens can also be irrigated during your vacation. The use of soaker or emitter hoses work best coupled with a timer. Set the timer for a twice per week soaking. The water you provide will keep your vegetables and flowers alive. If a sudden rainfall occurs while you are gone, your irrigation efforts won’t contribute to excess moisture problems.

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