Garden Variety: How to alleviate plant stress due to drainage issues

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Waterlogged garden.

Recent rains and cloudy days in the Lawrence area have resulted in standing water and wet soil in many yards and gardens. Excess water fills air space in the soil and suffocates plant roots, causing stress and making plants more susceptible to disease. This is a good time to identify areas where drainage could be improved and take measures to alleviate plant stress.

If water sits in an area after a heavy rainfall occurs but drains within 24 hours, plants are likely to be unaffected and soil improvements are probably unnecessary. If pools remain longer than a day or soil stays saturated and mucky for long periods, improvements are warranted.

The biggest problem with standing water and waterlogged soils from a plant health perspective is that excess water prevents oxygen from getting to plant roots. Plants need oxygen for a process called respiration. If plant cells are unable to respire for too long, they die. In cases of standing water and waterlogged soils, plant roots die and plant tops cannot be sustained.

Plants with damaged root systems may wilt, turn light green or yellow, shed leaves, and show other signs of plant stress. The first inclination is usually to give a plant showing these symptoms fertilizer, but that can encourage rapid growth and cause even more stress.

Stressed plants are more susceptible to disease and in these cases are especially likely to succumb to soilborne fungal and bacterial pathogens.

Unfortunately, there is little that can be done immediately to improve plant health. If plants are mulched heavily, pull mulch back from the base of the plant temporarily to allow soil to dry out. When or if soil becomes dry enough to work, add compost and mix it into the soil as well as possible without disturbing plant roots. If plants are small, consider lifting them out of the soil, mixing compost into the area, and replanting.

Compost is a good option for soil improvement both short-term and long-term because it increases pore space in the soil and alleviates compaction, allowing water to move through the soil profile more efficiently. When affected areas dry out enough to be worked, consider adding compost. Or, put compost addition on a fall garden to-do list.

For continual or more serious drainage issues, long-term solutions probably require major soil improvement or structural changes. These can range in difficulty depending on the size of the problem and plant material desired. For example, in a vegetable garden, the best options to alleviate drainage are to build raised beds or raised planting rows.

Ornamental plants may also benefit from growing in a raised bed. Landscape berms, which are basically a rounded mound of soil, are a popular option for planting trees, shrubs and flowers where soil cannot otherwise be easily improved. Berms are also a design characteristic that can add dimension to the landscape and offer screening and improved flexibility for plant material.

Another option is to take the opposite approach and dig out a wet area instead of building up over the top of it. This could mean the creation of a rain garden or bioswale, which are depressions designed with plants that can handle temporary flooding. Rain gardens and bioswales are meant to channel and filter stormwater runoff rather than directing it out of the property.

Finally, if plants are growing in an area where they constantly show signs of water stress, consider moving or replacing the plant with something more tolerant of the site conditions.

— Jennifer Smith is a former horticulture extension agent for K-State Research and Extension and horticulturist for Lawrence Parks and Recreation.


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