Why is Wet Feet Bad for Plants?

Have you ever wondered why, despite your best efforts at watering, some plants seem to wilt, yellow, or even perish over time? Perhaps the issue lies not in the quantity of water you’re providing but in the drainage and the plant’s ability to cope with ‘wet feet’.

This article delves into the science of why overly wet conditions can spell doom for many plants and how understanding this can revolutionise your approach to gardening.

The Science Behind Wet Feet in Plants

Understanding Plant Physiology and Water Needs

Plants require water, but like anything, too much of a good thing can be detrimental. Let’s explore the balance between hydration and saturation, focusing on how plants use water and why they need oxygen at their roots just as much as they need moisture.

The Consequences of Overwatering

Oxygen Deprivation

Waterlogged soil significantly impairs the availability of oxygen to plant roots, a condition known as anoxia. Normally, air spaces in the soil facilitate the exchange of gases, including oxygen, which roots require for respiration and energy production.

When these spaces are filled with water, oxygen supply is cut off, leading to root suffocation. This not only halts plant growth but can also lead to the death of the plant if the conditions persist.

And before you ask – yes, plants do intake oxygen through their roots. They also intake carbon dioxide and expel oxygen through their leaves during photosynthesis. This can come as a surprise when we’ve only been taught that plants breathe in carbon dioxide and expel oxygen.

Root Rot and Pathogen Proliferation

Constantly wet conditions are a breeding ground for various fungi and pathogens, notably Phytophthora spp. and Fusarium spp., which are responsible for root rot diseases. These pathogens thrive in anaerobic (oxygen-depleted) environments, quickly colonising and damaging the plant’s root systems.

Infected roots become discoloured, soft, and unable to absorb nutrients or water efficiently, often resulting in the plant’s premature death.

Nutrient Leaching

Excessive water can cause vital nutrients to be washed away from the soil, a process known as leaching. This deprives plants of the essential minerals they need for healthy growth and development.

Symptoms of nutrient deficiency include poor growth, yellowing leaves (chlorosis), and reduced flowering or fruiting, which can negatively impact the overall health and aesthetic appeal of the garden.

Impaired Growth and Vulnerability

The cumulative effect of oxygen deprivation, root rot, and nutrient leaching due to overwatering is a significant impairment in plant growth. Stunted growth, increased susceptibility to pests and diseases, and ultimately, plant decline are common outcomes.

Plants weakened by water stress are less able to withstand environmental challenges, making them more prone to infestations and other diseases.

Practical Advice for Preventing Wet Feet

Improving Your Garden’s Drainage

To prevent overwatering and ensure healthy plant growth, begin by evaluating your garden’s drainage capabilities. Signs of poor drainage include water pooling on the surface after rain, slow disappearance of water, and water-stained walls nearby. Improving drainage starts with understanding your garden’s specific needs and conditions.

You can add gypsum and organic matter to clay-dominant soils to improve drainage. This can help, but is not a silver bullet for many situations. You may need to add physical drains in the lower parts of the landscape, or alternatively install a rain garden which will help filter the water into the water table where plants can access it during drier periods.

Choosing the Right Plants

Selecting plants based on their tolerance to wet conditions can make a significant difference. Some species (and cultivated varieties) are more resilient and adapted to handle periods of excessive moisture, while others are highly susceptible to wet feet.

Researching and choosing the right plants for your garden’s conditions can prevent many issues associated with overwatering. Keep reading for some great examples of wet feet plants.

Improving Soil Structure and Drainage

Amending your garden’s soil can greatly enhance drainage and aeration. Incorporating organic matter, such as compost or well-rotted manure, can improve soil texture, encourage beneficial microbial activity, and promote better water infiltration and retention.

Think of organic matter like a sponge: it holds water, but not too tightly. When the soil is very clay-dominant, you can also add gypsum as discussed above. Beware not to add too much as you can leach nutrients such as iron.

Proper Watering Techniques

Adopting best practices for watering is important. This includes watering deeply but infrequently to encourage deep root systems, watering early in the morning, and using drip irrigation or soaker hoses to target water directly to the root zone, minimising waste and reducing foliage wetness that can lead to disease.

Using Raised Beds and Proper Planting Techniques

Raised beds can offer an effective solution to drainage problems by elevating the root zone above water-prone areas. Additionally, employing proper planting techniques, such as ensuring plants are not set too deeply in the soil and creating mounds or slopes for water to run off, can further help manage water in the garden effectively.

Ozbreed’s Wet Feet Trials: Identifying Plants That Can Tolerate Waterlogged Conditions

In an effort to address the challenges posed by waterlogged conditions in landscapes, Ozbreed has undertaken comprehensive ‘wet feet’ trials. These trials aimed to test the survivability of various landscape plants under extreme wet conditions, a concern increasingly relevant in the context of climate change and erratic weather patterns.

The trials were meticulously conducted across three distinct testing areas: heavy clay-type soil with constant water saturation, a bio-retention swale, and a floodplain, each presenting unique challenges to plant survival.

You can learn more about the studies here: 

Heavy Clay-Type Soil Testing Area

In this environment, characterised by its poor drainage and constant moisture, two varieties of Lomandra, namely Evergreen Baby™ Lomandra labill ‘LM600’ PBR and Shara™ Lomandra fluviatilis ‘ABU7’ PBR, demonstrated remarkable resilience, boasting a 100% survival rate.

Additionally, it was observed that the survival rate of Tanika® Lomandra longifolia ‘LM300’ PBR could be significantly enhanced (up to 62.5%) through treatments with Phyto guard and Rhizovital, showcasing the potential of targeted interventions in improving plant survivability under wet conditions.

Importantly, a traditional fungicide Agri-Fos actually made the situation worse, with a 0% survival rate compared with no treatment which had a 25% survival rate.

Bio-Retention Swale Testing Area

The bio-retention swale presented a varied picture of health and survivability among tested plants. It was noted that plant age played a critical role, with younger Pennisetum plants succumbing to the conditions while older specimens showed greater resilience. This area provided valuable insights into how different varieties of Rhaphiolepis, Lomandra, and Westringia respond to saturated conditions, highlighting the importance of establishing plants before flooding occurs.

Floodplain Testing Area

Perhaps the most challenging environment, the floodplain subjected plants to multiple flooding events. Despite these harsh conditions, several plants not only survived but thrived. Noteworthy performers included:

• Amethyst™ Liriope muscari ‘LIRTP’ PBR
• Just Right® Liriope muscari ‘LIRJ’ PBR
• Cosmic White™ Rhaphiolepis indica ‘RAPH01’ PBR
• Cosmic Pink™ Rhaphiolepis indica ‘RAPH02’ PBR
• Better John™ Callistemon viminalis ‘LJ1’ PBR
• Green John™ Callistemon viminalis ‘LJ23’ PBR
• Macarthur™ Callistemon viminalis ‘LC01’ PBR
• Slim™ Callistemon viminalis ‘CV01’ PBR
• Shara™ Lomandra fluviatilis ‘ABU7’ PBR
• Lucky Stripe™ Lomandra hystrix ‘LMV200’ PBR
• Tropic Cascade™ Lomandra hystrix ‘LHWP’ PBR

These results give us a decent palette of robust options for landscaping in flood-prone areas.

Plants Proven to Tolerate Wet Feet

Based on Ozbreed’s extensive trials, a list of plants has been identified that demonstrate a high tolerance to wet feet conditions, making them ideal candidates for inclusion in landscape designs subject to extreme weather or suboptimal irrigation practices. Some of these include:

• Lomandras: Evergreen Baby, Shara, and Tropic Cascade Lomandras
• Rhaphiolepis: Cosmic, Cosmic Pink Rhaphiolepis
• Liriopes: Amethyst, Just Right Liriopes
• Callistemons: Better John, Green John, Macarthur, Slim Callistemons
• Westringias: Mundi, Grey Box Westringias

These findings offer invaluable guidance for landscape architects, council decision-makers, and professional landscape experts in selecting plants capable of withstanding waterlogged conditions.

By integrating these resilient varieties into their projects, they can ensure the longevity and vibrancy of green spaces, even in the face of challenging environmental conditions.

If you’re interested in exploring the full range of plants tested and their responses to wet feet conditions, more information can be found on Ozbreed’s website: Summary of Plants in Various Wet Feet Conditions.

Conclusion: Embracing the Balance

While there are some plant varieties that have evolved or have been bred to withstand wet feet conditions, they are in the minority. Most plants prefer to have the soil moist but not wet.

Sometimes, the answer to wet feet is to tone down the irrigation. Other times, it’s about amending soil or providing extra drainage. Sometimes, you’re simply better off ripping unsuitable plants out of a wet area and replacing them with varieties more tolerant of the conditions.

Now that you understand why most plants can’t withstand wet feet, you understand how to remediate wet conditions, and you have a good plant palette that is resilient in the face of flooding, you should be prepared to operate even in the wettest of growing environments.

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