Do you have a plant that wilted down and never recovered despite you watering it when you noticed it was wilted? Or is your plant experiencing dieback? Does it have yellow leaves and stunted growth? If so. you are likely dealing with root rot.
As passion flower growers, root rot is something we are always on watch for. Passion flowers are highly susceptible to root rot as are a variety of other plants such as lavender, rosemary, succulents, vinca, petunias, etc. You can bet that if the plant tag states that the plant requires good drainage that it is susceptible to root rot.
What is root rot and how to recognize it
Root rot is caused by a soil pathogen, usually one of several different fungi. It invades the roots of your plant and causes the roots to die and rot off. Left unchecked, it will continue to rot the roots until your plant has nothing left. This can happen very quickly in waterlogged soil as the overly wet soil creates the perfect environment for the fungus to rapidly grow. There are also wilts that can be transmitted by insects, however they are different and that is a topic for another day.
In this article, we are concerned with root rot caused by over watering. The main symptoms of this type of root rot are wilting of plants, yellow leaves and stunted growth. If your plant has yellow leaves and stunted growth, you may be able to save it if you can get the soil to dry out quickly. Unfortunately, plants that suddenly wilted down are less likely to recover.
If you pull one of these plants out of their pot, you will usually see soggy soil and plant roots that are brown and wet or mushy looking rather than being white and plump. If the top of the soil in the pot is covered with moss, that is also a good indication that your plant is likely suffering from excess moisture.
The symptoms of over watering and under watering look virtually identical
It is important that you look not only at the plant’s leaves, but you also need to check the soil when you notice a problem with one of your plants. Many a well-intentioned gardener has watered and then watered again a plant because it was wilted. However, had they checked the soil before watering they would have realized that water was the last thing the poor plant needed.
The yellowing of leaves or stunting of growth courtesy of root rot can also look remarkably similar to a nutrient deficiency, or perhaps a disease. Again, this often results in inappropriate treatment of the ailment. Resulting in a dead plant and a confused gardener.
Before you water your plants check the soil
It is always a good policy to only water your plants after checking the soil moisture level. Don’t water them on a schedule or because you think they need it. Don’t water them because they are wilted without checking the soil either. Remember too much water looks the same as too little water and is just as harmful.
It only adds a few seconds to your watering routine to feel the soil for moisture. If the soil is sufficiently moist refrain from watering. Taking a few extra seconds can make the difference between a plant that thrives and one that is dead.
Plants that are root rot prone (including Passifora) benefit from having their soil almost completely dry out before getting watered. What we mean by ‘almost dry out’ is that the soil has dried to the point that the plant is just about to start wilting, or has wilted just a tiny bit. You don’t want them to wilt badly as this can cause the plant to die back or even completely die. However, allowing them to get to the point of almost wilting prior to watering can be very helpful, particularly in cooler weather.
It can also be a good policy to have a dry down day for plants that are susceptible to root rot. This is something we often do with our container grown passion flowers. It is also something that is commonly incorporated into lawn watering schedules. You simply skip your normal watering which allows the plants to get drier than they normally would.
How do we do our dry down days?
We simply skip or delay watering for one session. In the heat of summer, a ‘dry down day’ in our greenhouse might actually only be a watering delay of a few hours as the plants should be watered as soon as they start to show signs of drought stress. What we typically do is avoid watering on any cloudy or rainy day. This prevents the foliage from sitting wet, and also keeps us from over-watering the plants. The plants are not using nearly as much water on a cloudy, wet day as they are on a hot sunny day.
In the winter when it is exceptionally easy to rot out plants, we are even more careful to incorporate time for the plants to dry out into our watering schedule. We might have days and days of cold rainy weather where the greenhouse hardly gets above 50 degrees. In these conditions, sometimes our dry down day might stretch into days. We might avoid watering for a week or more if the plants are not showing any signs of drought stress.
This can be useful not only for passion flowers, but any plant that is intolerant of poor drainage.
Many plants that require excellent drainage are also drought tolerant. They are much less likely to be bothered by a temporary water shortage than they are by consistently wet soil. Many of them may even appreciate short temporary droughts.
Your soil type matters!
Plants grown in poorly drained or heavy clay soil can be more susceptible to root rot than those grown in lighter/sandy soils. Additionally, plants are more susceptible in cool weather. Fall/winter/spring often combines excess rainfall with poor drainage and dormant plants. This creates the perfect environment for rot to take hold. Often, it is actually excess moisture and the resulting rot that causes plants to fail to overwinter, not the cold temperatures.
It is important to carefully situate root rot prone plants or those that are marginally hardy in your climate. You will have the best chance of getting them to survive in a well-drained location. If you cannot provide a well-drained location you are better off switching out the plant for something tolerant of having wet feet.
Plants can drown similarly to how you could drown in a pond
Just like the top of your plant is alive, the roots of your plant are alive. Living organisms need to breathe and your plant roots are no exception. The air spaces between soil particles are components of soil equally as important as the dirt you can see. When soil is saturated with water the air spaces get filled up with water molecules and your plant’s roots are no longer able to breathe and they suffocate. This provides the perfect environment for root rots to take over and finish killing the plant.
Plants vary in their ability to tolerate soil saturation. Some plants can die within a few hours of being submerged. Others, such as those you often see in riparian areas are able to tolerate occasional flooding. Still others are able to live in permanently saturated soil. Some plants even have special roots designed to stick out of the water to get oxygen allowing them to live in permanently saturated soil.
Container grown plants can be particularly susceptible to root rot
This is why it is recommended to gradually pot up plants to slightly larger pots rather than putting a tiny little plant in a huge pot. It is too easy to over water and rot a small plant in a large pot, and even moisture tolerant plants may succumb to rot. This is also why you do not use regular soil in pots, but rather potting mixes. The soil from your garden holds far too much water and will rot your plants.
You may now be wondering, why are container plants more susceptible? After all when you plant a plant in the ground, it is going into an infinitely larger ‘container’ than the pot on your patio. However, there is a distinct (albeit invisible) difference between the two. Soil is not an inert substance your plant is growing in. It is rather one massive living breathing ‘organism’. It is full of bacteria, fungi, protozoa, insects, worms, plant roots, etc. While disease organisms are present in garden soil, healthy soil is balanced, and all the beneficial organisms keep the pathogens in check.
The media in your flowerpots is not part of that living soil organism. It is ‘dead’.
So without all the beneficial organisms present, it is easy for the pathogens to proliferate and overcome your plants. This is why you compensate by potting up plants gradually. By only adding a small amount of new soil, the plant is able to set roots out into it to absorb the excess moisture before the pathogens can take over.
Now, keep in mind, it is not a given that the soil in your garden is healthy. It is very possible to create unhealthy soil where pathogens can overwhelm your plants similarly to how they do so in containers. A good example of this is where they fumigate fields to plant crops like strawberries.
Fumigation kills off all the microorganisms in the soil both good and bad making that field similar to the container on your patio. Its a great thing in the short term because you killed off all the pathogens, but it also sets the soil up to be the perfect environment for pathogens to proliferate making the soil very bad for plants in the long term. So be sure to treat your soil with care and respect as the valuable living organism it is.
How to prevent root rot
Avoid over watering. This is the main cause of root rot. Check soil moisture before watering. Take steps to protect container plants from excess water if they are outdoors and you are going to have a week of rain. Improve your drainage both in containers and also your garden if you can.
If you garden tends towards soggy soil and you wish to grow plants intolerant of wet feet, you may be able to help them by planting them on mounds or in raised beds. This way their crowns and some of their roots will be above your saturated soil during the winter months. Additionally, you may be able to cover a raised bed with plastic to shed the winter rains helping to keep the plant drier.
Lastly, we would recommend that you do yourself a favor and select plants that prefer your soil type and moisture level. Remember there are plants that thrive in every environment from the desert to the swamps. Selecting plants that want to live in the environment you have will allow your garden to flourish with minimal work on your part.
We hope that this guide on root rot will help your plants to thrive this coming season.
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